SIMPLE IRA vs SEP IRA vs Solo 401(k) in 2026: Contribution Limits, Eligibility Cliffs, and Choosing the Right Plan for Your Business

The 2026 contribution limits side by side

Let’s start with the dollars because the numbers drive most of the conversation. Rev. Proc. 2024-40 and the related IRS Notice for 2026 set the inflation-adjusted limits, and the figures matter for the simple ira vs sep ira vs solo 401k comparison.

SIMPLE IRA. The 2026 employee elective deferral limit is $16,500. The age-50 catch-up is $3,500. The SECURE 2.0 §117 enhanced employer election (the 10 percent boost for small employers with 25 or fewer employees, or for employers electing to use higher matches) raises the regular limit to $17,600 and the catch-up to $3,850 in eligible plans. The new age-60-to-63 ‘super catch-up’ under SECURE 2.0 §109 is $5,250 for SIMPLE plans in 2026, layered on top of the regular catch-up for those four ages. Employer match is 3 percent of compensation (dollar for dollar up to 3 percent) or a 2 percent non-elective contribution to all eligible employees.

SEP IRA. Employer contributions only. The 2026 limit is the lesser of 25 percent of compensation or $69,000. For self-employed individuals the 25 percent applies to net earnings from self-employment after the deduction for one-half of SE tax and after the SEP contribution itself, which works out to roughly 20 percent of net SE income. No employee deferrals, no catch-up provision, no Roth bucket (until plans adopt the new SECURE 2.0 Roth SEP feature, which has been slow to roll out at custodians).

Solo 401(k). The 2026 employee elective deferral limit is $24,500 (same as a regular 401(k) under IRC §402(g)). The age-50 catch-up is $7,500. The age-60-to-63 super catch-up is $11,250. Employer profit-sharing contribution is up to 25 percent of compensation (about 20 percent of net SE income for sole proprietors), capped so that the combined employee plus employer total doesn’t exceed $69,000 in 2026 ($76,500 with regular catch-up, $80,250 with super catch-up).

For a 55-year-old self-employed earner pulling $200,000 of net SE income, the absolute maximums work out like this. SIMPLE: $16,500 + $3,500 + roughly $6,000 match = about $26,000. SEP: about $37,200 (roughly 20 percent of $186,000 of SE earnings after the SE tax adjustment). Solo 401(k): $23,500 + $7,500 + about $37,200 employer = roughly $68,200. The Solo 401(k) wins by nearly $42,000 over SIMPLE and $31,000 over SEP at this income level. That’s not a rounding error. That’s a different retirement.

At higher incomes the gap closes between SEP and Solo 401(k) because both hit the $69,000 cap. At $400,000 of net SE income, a 45-year-old contributes the same $69,000 either way. Below the cap the Solo 401(k) wins because the employee deferral isn’t tied to a percentage of comp.

The §415(c) limit. IRC §415(c) caps total contributions across both employee and employer sources at $69,000 in 2026 (or 100 percent of compensation, whichever is less). The age-50 catch-up at $7,500 sits outside this limit, bringing the effective ceiling for older participants to $76,500. The age-60-63 super catch-up at $11,250 raises it further to $80,250 for those four ages. These ceilings apply per plan, per related-employer group — not per individual, which matters for owners running multiple businesses.

Compensation cap. The IRC §401(a)(17) compensation limit is $350,000 for 2026. This caps the compensation that can be considered for plan contribution percentages. An owner earning $1,000,000 in W-2 from their S-corp can only treat $350,000 as ‘compensation’ for the 25 percent employer profit-sharing calculation. Result: maximum employer contribution is 25 percent of $350,000 = $87,500, but the §415(c) limit still caps the total at $69,000. The compensation cap matters more in defined-benefit plans where the limit governs accrual calculations.

Eligibility rules — who can adopt each plan

The eligibility filters are where things get messy. Pick the wrong plan for your situation and you’ll either be barred from contributing or forced to cover employees you didn’t expect to cover.

SIMPLE IRA. Available to employers with 100 or fewer employees who received at least $5,000 of compensation in the prior year. The employer cannot maintain another qualified retirement plan in the same year (an obvious exclusion that catches people who already have a SEP or 401(k) and try to add a SIMPLE). All employees who earned $5,000 or more in any two prior years and are reasonably expected to earn $5,000 in the current year must be eligible. The employee count is a hard cliff — go over 100 and you have a two-year grace period to wind down or convert.

SEP IRA. Available to any business form (sole prop, partnership, LLC, S-corp, C-corp). Eligible employees are those age 21 or older who have worked for the employer in at least three of the last five years and earned at least $750 in 2026. Here’s the cliff that catches people: the employer must contribute the same percentage of compensation for every eligible employee, including the owner. So a sole prop with no employees can stuff $50,000 into a SEP and only contribute for themselves. Add one part-time bookkeeper who’s been with you four of the last five years earning $30,000, and you now have to contribute the same percentage of her comp that you contributed to yourself. If you put 25 percent into your own SEP, you owe 25 percent of $30,000 = $7,500 to her account. Required, not optional.

Solo 401(k). Strictly for businesses with no full-time W-2 employees other than the owner and the owner’s spouse. The IRS defines full-time as 1,000 hours per year for plan years before 2024, or 500 hours per year for three consecutive years under the long-term part-time employee (LTPTE) rules added by the SECURE Act and accelerated to two years by SECURE 2.0. Independent contractors don’t count as employees. Once you hire your first W-2 employee who crosses the LTPTE threshold, your Solo 401(k) has to convert to a regular 401(k) with all the testing and disclosure that comes with it — or you have to terminate the plan.

The LTPTE rule under SECURE 2.0 §125 is a sleeper. A part-timer who works 500 hours per year for two consecutive years (years beginning in 2025) is now eligible for elective deferrals starting in 2026. That kills your Solo 401(k) status. If you’ve been running a Solo 401(k) and have a long-term part-timer who’s quietly crossed 500 hours each year, you have a problem coming.

Practical filter. If you have any W-2 employees other than a spouse, Solo 401(k) is out. If you have 100 or fewer employees and want them to participate, SIMPLE is in. If you have part-time-only or contractor-heavy staff and you don’t want them to participate, SEP forces you to cover them anyway, so SIMPLE or a regular 401(k) becomes the answer.

Roth options under each plan

SECURE 2.0 opened up Roth options across the small-business plan world. Whether you can actually use them depends on custodian rollout.

SIMPLE IRA Roth. SECURE 2.0 §601 added a Roth option to SIMPLE IRAs starting in 2023. The employer can amend the plan to permit Roth contributions, and employees can elect to designate part or all of their deferrals (and the employer match) as Roth. Custodian adoption has been uneven. Fidelity and Schwab support Roth SIMPLE deferrals; many smaller credit unions and regional banks still don’t. If Roth-eligibility matters to you, confirm with the custodian before signing the Form 5305-SIMPLE.

SEP IRA Roth. SECURE 2.0 §601 also opened SEP IRAs to Roth contributions. Employer contributions designated as Roth are immediately taxable to the employee. The mechanics require a W-2 reporting wrinkle that the IRS clarified in Notice 2024-2. As of 2026 the Roth SEP is technically available but practically rare because most custodians haven’t built the systems. Don’t count on Roth SEP availability unless your custodian explicitly confirms it.

Solo 401(k) Roth. The mature option. Solo 401(k) plans have offered designated Roth contributions (under IRC §402A) for many years. The employee deferral portion can be split between traditional and Roth in any ratio. SECURE 2.0 §604 added Roth employer contributions to Solo 401(k) plans too — the employer can designate profit-sharing contributions as Roth, which are immediately taxable to the participant. This is huge for owners who want maximum Roth exposure. A 55-year-old can put $7,500 catch-up + $23,500 deferral all into Roth, then designate the $37,000 employer profit-sharing as Roth too, for $68,000 of Roth contributions in a single year. No income limit (the backdoor Roth dance isn’t needed).

If Roth is a priority, Solo 401(k) is the clear winner in the simple ira vs sep ira vs solo 401k comparison. SIMPLE Roth and SEP Roth are technically available but custodian support is spotty.

The Roth-vs-traditional question. Designating contributions as Roth eliminates the current-year deduction in exchange for tax-free growth and tax-free qualified distributions. The choice depends on current vs. expected future marginal rates. Higher rates now, lower rates in retirement: traditional wins. Lower rates now, higher rates in retirement: Roth wins. Most retirees end up in lower brackets than their peak earning years, so traditional contributions typically beat Roth on pure tax-rate math. Roth wins for three other reasons: (a) no RMDs during the owner’s lifetime (since 2024 — SECURE 2.0 §325 eliminated lifetime RMDs from designated Roth accounts in qualified plans), (b) tax-free wealth transfer to heirs under the SECURE Act 10-year rule, and (c) protection against future tax law changes raising rates.

Owner age matters. Younger owners (under 40) generally benefit from Roth because the long compounding period makes the most of the value of tax-free growth. Older owners (55+) generally benefit from traditional because the remaining accumulation period is shorter and current bracket savings dominate. Middle-aged owners are case-by-case.

Reporting. Roth contributions show in W-2 Box 12 with code AA (designated Roth). Traditional contributions show with code D. The W-2 reporting drives the IRS’s tracking of contribution character; don’t let your payroll provider get this wrong.

Loan provisions — only one plan offers them

SIMPLE IRA. No loans. IRC §72(p) loan rules don’t apply because IRAs aren’t qualified plans subject to those rules, and IRAs are explicitly prohibited from making loans to participants. If you take any money out of a SIMPLE IRA before age 59½, you face a 10 percent early withdrawal penalty plus regular income tax. Worse, withdrawals within the first two years of SIMPLE participation get hit with a 25 percent penalty under IRC §72(t)(6).

SEP IRA. Same as SIMPLE — no loans permitted. SEP IRAs are IRAs, not qualified plans. Early withdrawals face the same 10 percent penalty under IRC §72(t).

Solo 401(k). Loans permitted if the plan document allows them. The maximum loan is the lesser of $50,000 or 50 percent of the vested account balance, with a five-year repayment term (longer for primary residence loans). The interest paid goes back to your own account. This is one of the underappreciated advantages of a Solo 401(k) for self-employed people who want a backup source of liquidity. You can’t access SIMPLE or SEP money without a tax hit; you can borrow from a Solo 401(k) without taxes if you repay on schedule.

Quick example: a 40-year-old Solo 401(k) participant with $200,000 in the plan needs $40,000 for a business expansion. Take the loan, repay over five years at 8 percent interest (about $812/month). Interest goes back to your own account. Total cost: zero tax, just the opportunity cost of the interest you’re paying yourself. The same person with a SEP would either pay the 10 percent penalty plus income tax (roughly 35 percent combined) on a $40,000 distribution = $14,000 of tax, or skip the SEP and use other capital.

Default loan setup. Most prototype Solo 401(k) plans at Fidelity, Schwab, and Vanguard either don’t include loan provisions or require the participant to elect them at plan adoption. Specialty Solo 401(k) providers (RocketDollar, Sense Financial, IRA Financial) generally include loan provisions by default. If you anticipate ever wanting plan liquidity, confirm the plan document permits loans before signing. Adding loan provisions after the fact requires a plan amendment — possible but takes paperwork.

Loan default consequences. If you fail to repay a Solo 401(k) loan on schedule (e.g., business slows down, payments stop), the unpaid balance is treated as a deemed distribution under IRC §72(p). The full unpaid amount is taxable in the year of default plus the 10 percent early withdrawal penalty if under 59½. So borrowing from your Solo 401(k) requires discipline — you need to actually make the payments. Many participants set up automatic ACH from their business checking account to ensure compliance.

Hardship distributions. SECURE 2.0 §312 added a self-certification provision for hardship distributions from 401(k) plans (including Solo 401(k)) — participants can certify their own hardship without documentation, simplifying the process. SIMPLE and SEP have no hardship provision because they’re IRAs (regular IRA early-withdrawal rules apply). For genuine emergencies, the Solo 401(k) flexibility on both loans and hardship distributions creates meaningful optionality.

Paperwork and administrative burden

The simple ira vs sep ira vs solo 401k decision often comes down to who wants to deal with the paperwork.

SIMPLE IRA setup. Adopt Form 5305-SIMPLE (a one-page IRS model document) or Form 5304-SIMPLE for the dual-custodian variant. Notify employees in writing 60 days before the effective date. Sign by October 1 of the year you want it effective. Filing requirements: no Form 5500, no annual reporting beyond the custodian’s standard 5498 and 1099-R for participants. Among the simplest qualified plans to maintain.

SEP IRA setup. Adopt Form 5305-SEP (the IRS model document) or a custodian’s prototype. Provide each eligible employee with a notice and a copy of the document. Effective date can be retroactive to January 1 of the prior year if adopted by the due date of the prior year’s tax return including extensions — this is a powerful feature for capturing prior-year deductions. No Form 5500 required. The custodian handles the administration.

Solo 401(k) setup. Adopt an IRS-approved prototype or custom plan document (Vanguard, Schwab, Fidelity all offer free prototypes; specialty firms like RocketDollar and Sense Financial offer self-directed plans). Sign the adoption agreement by December 31 of the plan year (SECURE Act extended this to the tax return due date for retroactive adoption, but employee deferrals still must be elected by December 31 — the extension only covers employer contributions). Annual Form 5500-EZ filing required once plan assets exceed $250,000 — one-page filing, but still a filing. Plan loans (if elected) require additional documentation. Most custodians charge $0 to $300 per year for Solo 401(k) administration.

Audit risk. Solo 401(k)s with no employees other than the owner and spouse have very low audit exposure. SIMPLE and SEP audits are rare because the model documents standardize compliance. The only real audit risk for any of these plans is contribution overages or employee eligibility errors.

The IRS provides good guidance — Publication 560 covers small-business retirement plans across all three types.

SECURE 2.0 changes hitting in 2026

SECURE 2.0 Act of 2022 dropped a stack of changes that phase in across 2024, 2025, 2026, and beyond. Here’s what matters for the simple ira vs sep ira vs solo 401k pick this year.

Mandatory auto-enrollment for new 401(k) plans (§101). Any 401(k) plan established after December 29, 2022 must auto-enroll employees at a minimum of 3 percent of compensation starting in 2025, escalating 1 percent per year to at least 10 percent. Solo 401(k) plans with no W-2 employees are technically subject to the rule but practically unaffected since the owner can elect their own deferral level. SIMPLE plans and SEPs are exempt from auto-enrollment requirements. If you’re starting a new 401(k) this year and you have employees, build the auto-enrollment into the plan from day one — the IRS will not be lenient on this.

Roth catch-up requirement for high earners (§603). Originally scheduled for 2024, the rule requires participants earning over $145,000 (indexed; $155,000 for 2026) in the prior year from the same employer to have their age-50 catch-up contributions designated as Roth. Notice 2023-62 delayed enforcement to 2026, and the IRS issued additional guidance in 2024 and 2025 clarifying the mechanics. As of 2026 the rule is in effect. SIMPLE IRA participants are subject to the rule too — high earners must use Roth catch-ups. SEP IRA participants are not (SEP doesn’t have a catch-up provision). Solo 401(k) owners earning over $155,000 from the business must designate catch-ups as Roth.

Super catch-up for ages 60 to 63 (§109). Effective 2025, participants aged 60 through 63 get an enhanced catch-up: the greater of $10,000 or 150 percent of the regular catch-up (for 2026, that’s $11,250 for 401(k)s and $5,250 for SIMPLE plans). This applies to all plan types that have catch-ups. SEP IRAs don’t have catch-ups so they don’t benefit.

Roth SIMPLE and Roth SEP availability (§601). Already discussed above — technically available, custodian-dependent in practice.

Increased SIMPLE limits for small employers (§117). Employers with 25 or fewer employees automatically get a 10 percent boost to the SIMPLE contribution limits, with corresponding required contributions (4 percent match or 3 percent non-elective). Employers with 26 to 100 employees can elect into the higher limits by providing the higher match. For 2026 the boosted limits are $17,600 deferral, $3,850 catch-up, $5,775 age-60-63 super catch-up.

Starter 401(k) plans (§121). A new simplified 401(k) option for employers with no current plan. Limited to elective deferrals up to the IRA contribution limit ($7,500 in 2026, including catch-up). No employer contributions, no testing. A middle ground between SIMPLE and full 401(k). Adoption has been slow because for most employers the SIMPLE remains the easier path.

Small employer startup credit (§102). SECURE 2.0 expanded the tax credit for small employers starting a new retirement plan. The credit covers 100 percent of startup costs (up to $5,000 per year for 3 years) for employers with 50 or fewer employees, plus a separate credit for employer contributions (up to $1,000 per employee per year for 5 years, phased out for higher-earning employees). The credit makes the cost of adopting any of these plans essentially zero for small employers. Owners frequently underestimate the credit value — a small employer adopting a SIMPLE or 401(k) and contributing to employee accounts can recover $5,000-$50,000 of federal tax credits over the first 5 years.

When SIMPLE IRA wins — the small-employer scenario

SIMPLE IRA is the right answer for one specific situation: a small employer with W-2 employees who wants to offer a retirement benefit without the complexity of a 401(k). It’s not the highest-contribution option for the owner, but it’s the easiest plan to administer that still covers a team.

Typical fit: a 15-person professional services firm or restaurant or specialty retailer. Owner wants to contribute and offer the staff a meaningful benefit, doesn’t want to deal with discrimination testing or Form 5500 audits, isn’t trying to stuff $60,000 into the owner’s account.

Cost. Custodian fees are typically zero or minimal — Fidelity, Schwab, Vanguard all offer free SIMPLE IRA programs for small businesses. The employer match (3 percent of compensation) is the main cost, plus the owner’s own deferral.

Example. 12-employee firm, $1.5M payroll, owner takes $200,000 W-2. Employer 3 percent match: $45,000 across the team. Owner’s contribution: $16,500 deferral + $3,500 catch-up (if 50+) + $6,000 match = $26,000 to owner’s account. Total annual cost: $45,000 employer match + $26,000 owner contributions. Deduction to the business: $51,000 (employer match + owner deferral, both deductible at the business level via reduced W-2). Roughly $18,000 of federal tax savings at 35 percent combined federal+state.

SECURE 2.0 boost. With 25 or fewer employees, the boosted limits apply automatically. Owner can defer $17,600 + $3,850 catch-up = $21,450 plus the $5,250 super catch-up if aged 60-63. Total potential for older owner: about $26,700 of personal deferrals plus the employer match.

Where SIMPLE fails. If the owner is trying to put away more than $30,000-$40,000 personally, the SIMPLE caps are too low. Either accept the limit and use a backdoor Roth for additional savings, or switch to a 401(k).

When SEP IRA wins — the solo professional with no employees

SEP IRA shines for one demographic: solo earners with no employees and no plan to hire, who don’t need Roth and don’t need loans, and who value extreme administrative simplicity.

The case for SEP. Adopt Form 5305-SEP in five minutes online. Contribute up to 25 percent of compensation (about 20 percent of net SE income) up to $69,000. Skip a year if you want — SEP contributions are entirely discretionary. Vary the percentage year to year. No annual filings. Custodian handles everything.

Typical fit: a consultant, freelance writer, contract physician, or single-member LLC with no W-2 employees. Income variable year to year. Doesn’t want to commit to any particular contribution schedule. Doesn’t care about Roth.

Example. Consultant with $250,000 of net SE income, age 45. SEP contribution: approximately $46,500 (about 20 percent of net SE income after the SE tax deduction). Same person under Solo 401(k): $23,500 + $46,500 employer = $70,000 (capped at $69,000). Solo 401(k) wins by $22,500. So why would you ever pick SEP over Solo 401(k)?

Reasons people still pick SEP. (1) Retroactive funding to the prior year — you can adopt a SEP and fund the prior year’s contribution by the extended tax return due date (October 15). Solo 401(k) employee deferrals must be elected by December 31 of the plan year, though the plan itself can be retroactively adopted by the tax return due date under SECURE Act §201. So a self-employed person who wakes up in March realizing they want to make a 2025 contribution can adopt a SEP and fund the full amount; with a Solo 401(k) they can only do the employer portion. (2) No annual Form 5500-EZ filing once Solo 401(k) assets cross $250,000. (3) Simpler custodian relationships at smaller firms.

These reasons are getting weaker over time as more custodians offer easy Solo 401(k) administration. SECURE Act §201 effectively eliminates most of the SEP’s retroactive-adoption advantage by extending Solo 401(k) adoption to the tax return due date.

Where SEP fails hard. The moment the owner hires even one part-time employee who hits the three-of-five-years rule, the SEP forces the owner to contribute the same percentage to that employee’s account. A solo practitioner contributing 25 percent of their $200K = $50,000 to themselves, who hires a part-time admin at $40,000, now owes 25 percent of $40,000 = $10,000 to the admin’s SEP account. Required. No vesting schedule allowed. The admin owns it immediately. Owners who don’t see this coming get blindsided.

The pro-rata SEP problem and backdoor Roth. SEP IRA balances aggregate with other traditional IRA balances for the pro-rata rule under IRC §408(d)(2). An owner running a backdoor Roth strategy who has $200,000 of SEP IRA assets and tries to convert a $7,500 nondeductible IRA contribution to Roth will trigger the pro-rata calculation. The result: roughly 97 percent of the conversion is taxable because 97 percent of the owner’s traditional IRA assets are pretax SEP balances. This kills the backdoor Roth strategy. Owners running backdoor Roths must roll the SEP balance into a Solo 401(k) (or other qualified plan that accepts IRA rollovers) before December 31 to clear the pro-rata math. Annual cycle: contribute to SEP for the deduction, then roll to Solo 401(k) before year-end to enable backdoor Roth. This is a real workflow for some self-employed clients but it adds complexity that Solo 401(k) alone avoids.

Specialty SEP variants. The SEP IRA is the only retirement plan available through Form 5305-SEP, but some custodians offer ‘prototype SEP’ plans that allow features not available in the model form (such as more restrictive eligibility, vesting schedules within certain limits). These prototype plans require more paperwork and rarely make sense for true solo earners. Stick with Form 5305-SEP unless you have a specific reason to deviate.

When Solo 401(k) wins — the highest-contribution play

Solo 401(k) is the default best answer for most self-employed people without W-2 employees. It maxes out faster than SEP at all but the highest incomes, offers Roth, offers loans, and the administrative burden is manageable.

Income level matters. Below about $250,000 of net SE income, the Solo 401(k) clearly wins because the $23,500 employee deferral isn’t tied to a comp percentage. A self-employed person at $80,000 of SE income contributes $23,500 deferral + about $14,900 employer = $38,400 to a Solo 401(k); the SEP would only allow $14,900.

At higher incomes ($350,000+ of net SE income), both Solo 401(k) and SEP hit the $69,000 ceiling. The choice then comes down to Roth availability (Solo 401(k) wins) and loan provisions (Solo 401(k) wins).

The Mega Backdoor Roth angle. A Solo 401(k) plan document that permits after-tax employee contributions and in-plan Roth conversions opens the door to a Mega Backdoor Roth. The owner can contribute the full $69,000 limit minus the regular employee deferral as after-tax contributions, then convert those to Roth. Functionally this creates Roth contributions far in excess of the normal Roth IRA limit. Standard custodian prototypes (Fidelity, Schwab, Vanguard) generally don’t support this; specialty Solo 401(k) providers do. Worth the extra setup cost if you’re trying to fill a Roth bucket aggressively.

Example. 50-year-old solo earner, $400,000 of net SE income. Adopts a custom Solo 401(k) with Mega Backdoor Roth. Contributes $23,500 traditional employee deferral + $7,500 catch-up Roth + $37,000 employer profit sharing + $46,500 after-tax converted to Roth (filling up the §415 limit which is separate from the $70,000 §415(c) limit on contributions in this analysis). Total: about $114,500 of retirement contributions, with $54,000 of it in Roth. None of this is possible in a SEP or SIMPLE.

The Solo 401(k) is the clear answer for serious savers. The administrative cost is real but minor — Form 5500-EZ once you cross $250,000 in plan assets, plus a yearly check that your plan document is up to date. Most owners spend an hour a year on it.

Conversion paths between plans

Sometimes you adopt the wrong plan or your situation changes. Here’s how to move between them.

SIMPLE to SEP. Wait. SIMPLE IRAs can’t be terminated mid-year. You must continue contributions through December 31 of the year you want to terminate, then adopt the new plan effective January 1 of the next year. Existing SIMPLE balances stay where they are or can be rolled to a SEP IRA, traditional IRA, or another qualified plan (but a SIMPLE-to-non-SIMPLE rollover is barred during the first two years of SIMPLE participation under IRC §408(d)(3)(G) — early rollovers face a 25 percent penalty).

SIMPLE to Solo 401(k). Same wait-until-year-end rule. After two years of SIMPLE participation, balances can be rolled to the new Solo 401(k). Within the first two years, the balance stays in the SIMPLE IRA until the two-year period expires.

SEP to Solo 401(k). Easier. The SEP can be terminated by stopping employer contributions; no formal termination required. The SEP IRA balance rolls into the Solo 401(k) without restriction (IRA-to-qualified plan rollover under IRC §408(d)(3)). The owner can adopt the Solo 401(k) effective the same year and contribute under the new plan’s rules, with the wrinkle that the SEP and Solo 401(k) shouldn’t both receive contributions in the same year for the same earnings (the plans share the $70,000 §415(c) limit when sponsored by the same employer).

Solo 401(k) to SIMPLE. Rare. Why would you give up the higher limits and loan provisions? Possible if you’re scaling back business activity and want simpler administration. The 401(k) must be formally terminated; participants receive a final distribution or rollover. Then adopt the SIMPLE.

Mid-year transitions. SECURE 2.0 §332 created a new pathway for mid-year transition from SIMPLE IRA to a safe harbor 401(k). Effective 2024, an employer can convert a SIMPLE to a safe harbor 401(k) mid-year if the SIMPLE is replaced with a plan that meets certain conditions. The two-year withdrawal restriction on the SIMPLE balances is also waived in this scenario. Useful for growing businesses that outgrow the SIMPLE format.

Decision framework — picking your plan

Run through these questions in order to settle the simple ira vs sep ira vs solo 401k question.

1. Do you have W-2 employees other than yourself and your spouse? If yes, Solo 401(k) is out. Choose between SIMPLE and a regular 401(k) (which is beyond this article’s scope). If no, you have all three options.

2. Do you have part-time staff or long-term contractors who might qualify as employees under the LTPTE rules or who might trip the SEP coverage rule? If yes, lean toward SIMPLE (where you control employee participation thresholds at $5,000 of compensation) or a regular 401(k). If no, Solo 401(k) or SEP are clean.

3. Do you want to contribute more than $30,000 per year? If yes, SIMPLE is undersized. Move to SEP or Solo 401(k). If no, SIMPLE is plenty.

4. Do you want Roth contributions? If yes, Solo 401(k) is the strongest answer (mature Roth support, no income limit). SIMPLE Roth and SEP Roth are technically available but custodian support is spotty.

5. Do you want to be able to borrow from the plan? If yes, Solo 401(k) is the only option. SIMPLE and SEP prohibit loans.

6. Do you want minimum paperwork? If yes, SEP is the simplest of the three for a true solo earner. SIMPLE is next. Solo 401(k) requires Form 5500-EZ filing once assets cross $250,000.

7. Do you sometimes want to skip a year’s contribution? SEP allows full discretion year to year. SIMPLE requires the employer to maintain the plan and make the match for any employee who defers. Solo 401(k) allows full discretion on the employer profit-sharing portion.

Most common conclusion at the firm. Self-employed with no employees, serious about saving, wants Roth flexibility: Solo 401(k). Self-employed with no employees, casual saver who values simplicity above all else: SEP. Small employer with W-2 staff who wants to offer a meaningful benefit without complexity: SIMPLE. Small employer with high-earning owners who want maximum contributions: regular safe-harbor 401(k), beyond the scope of this comparison.

The simple ira vs sep ira vs solo 401k decision isn’t permanent. Plans can be switched as the business grows. Pick the plan that fits your situation today, revisit annually.

State tax interactions and multi-state considerations

Federal retirement plan rules are uniform across states, but state tax treatment varies in ways that affect the simple ira vs sep ira vs solo 401k decision for owners in certain jurisdictions.

California. State conforms to federal treatment of SIMPLE, SEP, and Solo 401(k) contributions — deferrals and employer contributions reduce state taxable income. California’s marginal rates run 9.3 percent to 13.3 percent at high incomes, so the state deduction on a $50,000 Solo 401(k) contribution can save $4,650-$6,650 of state tax. California does NOT conform to qualified plan loan rules in one corner case — a defaulted loan treated as a deemed distribution is taxable for state purposes too, but California’s mental health services tax (an additional 1 percent on income over $1 million) can hit older participants who default on large loans.

New York. Conforms to federal. State pension exclusion of up to $20,000 per year applies to qualified plan distributions for participants 59½ and older — so traditional Solo 401(k) and SIMPLE distributions in retirement get a New York income tax break that Roth distributions don’t need. This actually favors traditional contributions over Roth at the state level for retiring New Yorkers, partially offsetting the federal Roth advantage.

Pennsylvania. Conforms to federal for SIMPLE, SEP, and Solo 401(k) contribution deductions. But Pennsylvania doesn’t tax qualified plan distributions to participants 59½+ — distributions are entirely state-tax-free. This creates a huge after-tax advantage for traditional pretax contributions over Roth for Pennsylvania retirees.

No-tax states (Texas, Florida, Tennessee, Nevada, South Dakota, Wyoming, Washington, Alaska, New Hampshire on wages). State tax considerations don’t apply. Federal-only analysis governs the plan choice.

Multi-state employers. If you run a business with employees in multiple states, the state nexus and withholding rules for SIMPLE IRA deferrals add small administrative wrinkles. The retirement plan itself is governed by federal law regardless of state. State income tax withholding on employee deferrals follows the employee’s state of residence and the employer’s state nexus rules — your payroll provider handles this.

Non-resident state retirement plan participation. A consultant who lives in Texas (no state tax) but performs services in California has California-source income subject to California tax. Solo 401(k) contributions reduce California source income, providing California tax savings. The interaction of multi-state taxation and retirement plan contributions can be material for high-income mobile workers.

Coordination with other retirement vehicles

The simple ira vs sep ira vs solo 401k pick isn’t made in isolation. Other retirement accounts (IRAs, HSAs, cash balance plans) interact with the small-business plan choice in ways that affect total retirement savings capacity.

Backdoor Roth IRA interaction. The backdoor Roth IRA strategy involves making a nondeductible traditional IRA contribution and immediately converting it to Roth. The conversion is tax-free if the participant has no other pretax IRA balances (the pro-rata rule under IRC §408(d)(2) aggregates all traditional IRAs for the basis calculation). SEP IRA balances are aggregated for pro-rata purposes. SIMPLE IRA balances are aggregated for pro-rata purposes. Solo 401(k) balances are NOT aggregated — qualified plan balances stay out of the pro-rata math. For owners running a backdoor Roth strategy, Solo 401(k) is the clean choice. SEP and SIMPLE balances pollute the backdoor Roth and force tax on conversion.

Mega Backdoor Roth interaction. Solo 401(k) plans permitting after-tax employee contributions and in-plan Roth conversions enable the Mega Backdoor Roth. SIMPLE and SEP don’t support this. If making the most of Roth contributions is the goal, Solo 401(k) is the only path.

HSA stacking. Health Savings Accounts ($4,400 single / $8,750 family for 2026) provide a separate pretax retirement vehicle for those with HSA-eligible high-deductible health plans. HSA contributions stack on top of all retirement plan contributions — no interaction with §402(g) or §415(c) limits. Owners building maximum retirement savings should fund the HSA in addition to the SIMPLE, SEP, or Solo 401(k).

Cash balance plans. For high-income business owners (typically $400,000+) hitting the Solo 401(k) §415(c) limit, a cash balance plan layered on top can add another $100,000-$300,000 of annual deductible contributions. See Cash Balance Plan for Business Owners for the full mechanics. SIMPLE and SEP don’t pair well with cash balance plans because the contribution structure doesn’t coordinate. Solo 401(k) plus cash balance is the maximum-contribution combo.

Personal IRA contributions. Owners can still contribute to a personal traditional IRA ($7,500 in 2026, $9,000 with catch-up) alongside any SIMPLE, SEP, or Solo 401(k). The deduction is phased out at higher incomes if the owner is covered by an employer plan ($79K-$89K MAGI phaseout for single filers in 2026). Roth IRA contributions are also subject to income phaseouts ($153K-$168K single in 2026), but the backdoor Roth strategy works around the phaseout.

Spousal IRA contributions. A non-working spouse can contribute to a spousal IRA up to the contribution limit ($7,500 + $1,000 catch-up). If your spouse doesn’t work outside the home, this is an additional $8,500/year of retirement savings, fully independent of your SIMPLE/SEP/Solo 401(k).

Common mistakes that cost real money

Owners screw up these plans in predictable ways. Avoid the common ones.

Adopting a SIMPLE then realizing you wanted higher contributions. The SIMPLE can’t be terminated mid-year. You’re stuck contributing under SIMPLE rules through December 31. If you adopt the SIMPLE in January and decide in March that you want to upgrade to a Solo 401(k), you can’t — you have to ride out the year. Plan the decision before October 1 of the prior year.

Hiring a part-time employee under a SEP without realizing the coverage hit. The three-of-five-years rule catches people. A part-timer who worked for you in 2022, 2023, 2024, 2025 (any three of the last five) and earned $750 or more in 2026 is now eligible. If you contributed 25 percent to yourself in 2026, you owe 25 percent of that employee’s comp. Discovering this in February of the following year as your CPA prepares the return = ugly conversation. Track part-timer history actively.

Solo 401(k) auto-failure from a long-term part-timer. Under SECURE 2.0 §125, a part-time employee with 500+ hours in two consecutive years (starting 2025) qualifies for elective deferrals starting 2026. If you have a Solo 401(k) and a long-term part-timer hits the threshold, your Solo 401(k) status is gone. Plan must convert to a regular 401(k) or terminate. Audit your part-timer hours every year.

Missing the Solo 401(k) elective deferral deadline. Employee elective deferrals must be elected by December 31 of the plan year. The plan itself can be adopted retroactively under SECURE Act §201, but the employee deferral portion is forfeited if not elected by year-end. Self-employed people who file their tax return in March of the following year and realize they wanted to defer often miss this. Set up the Solo 401(k) and execute a salary deferral election before December 31.

Over-contributing to a Solo 401(k). The $70,000 §415(c) limit is per employer. If you have a Solo 401(k) and a separate employer where you also have a 401(k), the $23,500 §402(g) limit on elective deferrals applies across both plans (one employee, one limit). Owners who don’t aggregate the deferrals over-contribute. Excess contributions must be withdrawn by April 15 of the following year or face double taxation.

Missing the Form 5500-EZ filing. Once Solo 401(k) plan assets cross $250,000 on December 31, the plan is required to file Form 5500-EZ by July 31 of the following year. Penalty for failure to file: $250/day, capped at $150,000 per year. The Department of Labor offers a Delinquent Filer Voluntary Compliance Program at $500 per year for the first year and reduced rates thereafter. Easier to just file on time.

How The Reed Corporation handles the plan selection

Plan selection conversations with our clients typically follow a tight pattern. We pull the current employer structure (W-2 employees, contractor relationships, expected hires), the income trajectory (current and projected next three years), the retirement savings priority (max savings vs. employee benefit vs. owner only), and the Roth/loan preferences. Three to five plan options drop out, usually two are real contenders, and we pick.

For self-employed solo earners over $100,000 of SE income, our default recommendation is a Solo 401(k) with a specialty provider (RocketDollar, Sense Financial, or similar) that supports after-tax contributions for the Mega Backdoor Roth. Standard prototype Solo 401(k)s at Fidelity/Schwab/Vanguard are fine for most cases; the specialty providers cost an extra $300-600/year and access additional contribution capacity.

For small employers (5-50 W-2 employees) with no plan today, our default is SIMPLE IRA with the SECURE 2.0 §117 enhanced limits. The administrative burden is minimal, the employee benefit is meaningful, and the owner’s deferral capacity (up to $26,000 with catch-ups) covers most owners’ needs. If the owner is trying to put away more than $30,000 personally, we move the conversation to a safe-harbor 401(k) with profit-sharing.

For multi-entity setups (owner has both an S-corp and a Schedule C activity, or owns multiple businesses), we run the controlled-group and affiliated-service-group rules under IRC §414(b), (c), (m), and (o) to determine which plans can be coordinated and which must be aggregated. This is where DIY plan selection goes off the rails — owners assume each entity gets its own $69,000 limit, but controlled-group rules often force aggregation.

We coordinate the plan selection with the rest of the tax picture — see Strategic Tax Advisory for the broader retirement strategy conversation, or Tax Strategy Consulting for entity-level structuring. Retirement Planning covers the personal side of the retirement picture, including the interaction between business retirement plans and personal accounts like backdoor Roths.