Form 1040 Line 21: Other Taxes
What Feeds Into Line 21
Line 21 pulls from Schedule 2, Part II. That schedule collects taxes computed on separate forms and worksheets, then funnels the total into a single number on the main 1040. The most common items:
- Self-employment tax (Schedule SE)
- Additional Medicare tax (Form 8959)
- Net investment income tax (Form 8960)
- Early distribution penalty on retirement accounts (10% additional tax)
- Household employment tax (Schedule H)
- First-time homebuyer credit repayment
- Section 965 net tax liability installment from the 2017 transition tax
Self-Employment Tax
This is the one that shocks first-time freelancers. When you’re an employee, your employer pays half of Social Security and Medicare taxes (7.65%), and you pay the other half through withholding. When you’re self-employed, you pay both halves—15.3% on net self-employment income up to the Social Security wage base ($168,600 for 2025), and 2.9% Medicare tax on everything above that.
The calculation happens on Schedule SE. You first multiply net self-employment earnings by 92.35% (this approximates the employer-equivalent portion), then apply the 15.3% rate. The deductible half of self-employment tax—the employer-equivalent portion—goes on Schedule 1 as an adjustment to income. But the full tax amount hits Line 21.
A freelancer earning $150,000 in net self-employment income will owe roughly $21,200 in self-employment tax alone, on top of regular income tax. That’s often the biggest surprise on a first-year freelancer’s return.
Additional Medicare Tax
Since 2013, wages and self-employment income above $200,000 (single) or $250,000 (married filing jointly) face an additional 0.9% Medicare tax. Your employer should withhold this once your wages cross $200,000 at that job, but there’s a catch: the withholding threshold is per-employer, while the tax threshold is per-return.
If you earn $150,000 at each of two jobs, neither employer withholds the additional Medicare tax (you didn’t cross $200,000 at either one). But your combined wages are $300,000, so you owe the 0.9% surtax on $100,000. That’s $900 you’ll need to account for, and it shows up through Form 8959 on Line 21.
Net Investment Income Tax (NIIT)
The 3.8% NIIT applies to the lesser of (a) your net investment income or (b) the amount by which your MAGI exceeds $200,000 (single) or $250,000 (joint). Investment income includes interest, dividends, capital gains, rental income, and royalties—but not distributions from an active trade or business in which you materially participate.
This catches people in big capital gain years. Sell a rental property for a $400,000 gain while your MAGI is $300,000? You’ll owe NIIT on the excess over $250,000 (if filing jointly)—potentially $1,900 in addition to capital gains tax. Form 8960 computes this and sends it to Schedule 2.
Early Distribution Penalties
Withdraw from a traditional IRA or 401(k) before age 59½ without an exception, and you’ll owe a 10% additional tax on the taxable amount. The distribution itself is taxed as ordinary income (reported elsewhere on the 1040), and then this 10% penalty stacks on top via Line 21.
Exceptions to the 10% penalty include disability, substantially equal periodic payments (72(t) distributions), qualified first-time homebuyer expenses (up to $10,000 from an IRA), and certain medical expenses exceeding 7.5% of AGI. Roth IRA contributions (not earnings) can always be withdrawn penalty-free since they were already taxed.
Household Employment Tax
If you paid a nanny, housekeeper, or other household employee $2,700 or more in 2025, you’re a household employer. Schedule H calculates the Social Security and Medicare taxes you owe on their wages. Many people don’t realize this obligation exists until they apply for a government position or get audited.
The so-called “nanny tax” includes both the employer share (7.65%) and the employee share if you chose not to withhold it from their pay. You may also owe federal unemployment tax (FUTA) if you paid $1,000 or more in any quarter.
First-Time Homebuyer Credit Repayment
This is a legacy item. Taxpayers who claimed the 2008 version of the first-time homebuyer credit (which was really an interest-free loan of up to $7,500) are still repaying it in $500 annual installments. If you sold the home or stopped using it as your main home, the remaining balance comes due. It’s increasingly rare but still shows up on some returns.
A Counterintuitive Point
Self-employment tax can actually exceed your income tax. A single freelancer earning $60,000 in net self-employment income would owe roughly $8,478 in self-employment tax. After the standard deduction and the deductible half of SE tax, their federal income tax might be around $4,500—meaning the payroll-style tax is nearly double their income tax. Most W-2 employees never see this because the employer’s share is invisible to them.
How Line 21 Connects to Your Total Tax
Line 21 gets added to the result of Lines 14 through 20 to produce Line 22, your total tax. This is the figure that gets compared against your payments and withholding to determine whether you get a refund or owe a balance. Because Line 21 taxes are added after most credits, they can’t be offset by nonrefundable credits like the foreign tax credit or education credits—only by payments, withholding, and refundable credits.
Sources & References
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