ISOs vs. NSOs: Quick Breakdown

Non-Qualified Stock Options (NSOs) are taxed at exercise under IRC Section 83. The spread — the difference between your strike price and the fair market value when you exercise — is ordinary income. It shows up on your W-2, your employer withholds taxes, and you owe federal plus California income tax on the entire amount. For someone in the top brackets, that’s 37% federal plus 13.3% state, bringing the combined marginal rate on the exercise spread above 50%.

Incentive Stock Options (ISOs) work differently under IRC Section 422. There’s no ordinary income tax at exercise under federal rules. Instead, the spread becomes an adjustment for the Alternative Minimum Tax (AMT). If the AMT calculation produces a higher tax than your regular return, you owe the difference. The idea is that you defer tax until you sell the shares, and if you meet the holding requirements, the gain is taxed as long-term capital gains.

Here’s the California problem: the state doesn’t recognize the ISO deferral the way the federal government does. California conforms to the federal AMT framework, but the state’s AMT exemption amounts are much lower. A Californian can owe state AMT on an ISO exercise even when the federal AMT doesn’t apply.

California’s 13.3% Rate and No Capital Gains Break

At the federal level, long-term capital gains get taxed at 0%, 15%, or 20% depending on your income. That’s a meaningful discount compared to ordinary income rates that top out at 37%.

California doesn’t care. The state taxes capital gains as ordinary income. There is no preferential rate. So even if you hold your ISO shares for the required periods and get long-term capital gains treatment federally, California taxes the entire gain at your marginal rate — up to 13.3%.

This flattens the advantage of ISOs for California residents. The federal savings from qualifying for capital gains treatment is real, but the state-level benefit that employees in Texas or Florida get (zero state tax on the gain) doesn’t exist here. You’re paying 13.3% on the profit regardless of how long you held the shares. Compare this to New York, which at least offers some distinction at the state level.

For someone exercising $200,000 in options, the California tax alone is around $26,600 at the top rate. That’s a significant number, and it’s the same whether the income is classified as ordinary or capital gains at the state level.

The AMT Trap for ISO Holders

The Alternative Minimum Tax catches a lot of LA employees off guard. You exercise ISOs, there’s no W-2 income from the exercise, no withholding, and no immediate bill. Then tax season arrives and your CPA runs the AMT calculation using IRS Form 6251.

Federal AMT rates are 26% on the first portion of AMT income and 28% above that under IRC Section 55. But the real surprise for Californians is the state AMT, which applies at a lower exemption threshold. An employee who exercises $100,000 in ISO spread might not owe federal AMT but could still owe California AMT — and California doesn’t offer an AMT credit carryforward the same way the federal system does.

The worst-case scenario: you exercise ISOs late in the year, the stock price drops before you can sell, and you owe AMT on a gain that no longer exists. You’re paying tax on phantom income. This happened on a large scale during the 2000-2001 tech crash, and it still catches employees at pre-IPO companies and volatile tech stocks today.

Qualifying vs. Disqualifying Dispositions

ISOs get their preferred tax treatment only if you hold the shares for at least one year after exercise and two years after the grant date per IRC Section 422(a)(1). Meet both requirements (a qualifying disposition), and the gain is long-term capital gains federally. Miss either one (a disqualifying disposition), and the exercise spread becomes ordinary income — same as an NSO.

The federal difference between qualifying and disqualifying can be 17+ percentage points (37% ordinary vs. 20% capital gains). In California, the state tax is the same either way — up to 13.3%. So the total tax difference between qualifying and disqualifying a disposition for a California resident is smaller than it would be for someone in Florida or Texas, but it’s still worth planning around.

If you’re going to hold ISO shares, the holding period clock starts at exercise. Sell one day too early and the entire exercise spread is reclassified as ordinary income. We’ve seen employees miss the one-year mark by a week because they didn’t track the date.

Exercise Timing and Strategy

Exercising all your options in a single year is the most expensive approach in California. The state’s top bracket kicks in at relatively low income levels compared to other states — $1 million for the 13.3% surcharge per the FTB rate schedule. A large exercise can push you into that bracket even if your base salary wouldn’t.

Spreading exercises across multiple years keeps your income lower in each year, potentially keeping you below the $1 million threshold for the Mental Health Services Tax (the extra 1% that makes California’s top rate 13.3% instead of 12.3%).

Early exercise is another option if your company allows it. You exercise before the shares vest, file an 83(b) election within 30 days, and start the capital gains clock immediately. If the stock price is low at that point, the spread is small (or zero), which minimizes or eliminates the AMT adjustment. The risk: if you leave the company before the shares vest, you’ve paid for shares you have to give back.

For NSOs, a cashless exercise (exercise and sell simultaneously) is the simplest path. The broker handles withholding, you get cash, and there’s no ongoing tax uncertainty. The downside is that you give up any future appreciation on those shares.

Source-State Allocation if You Move

California taxes stock option income based on where you worked during the period the options were earned. If your options vested over four years and you worked in LA for three of those years, California claims 75% of the exercise spread as California-source income — even if you exercised after moving to Nevada or Texas.

The Franchise Tax Board is aggressive about this. Moving out of California before exercising doesn’t eliminate your California tax liability on those options. It reduces it proportionally, but the portion attributable to California work years is still taxable by the state per FTB sourcing guidelines.

If you’re planning a move, exercise timing matters. Exercising before you leave locks in California’s full rate on the entire spread. Exercising after you leave, in a state with no income tax, still subjects the California-earned portion to state tax — but saves you on the rest. Some employees relocate to Florida before exercising to minimize the non-California portion.

Sources & References

• 26 U.S.C. § 422 — Incentive Stock Options
• 26 U.S.C. § 83 — Property Transferred in Connection with Performance of Services
• 26 U.S.C. § 55 — Alternative Minimum Tax
• IRS Form 6251 — Alternative Minimum Tax
• IRS — 83(b) Election Information
• California FTB — Personal Income Tax Rates
• California FTB — Capital Gains and Losses
• California Franchise Tax Board