Stock Option Tax Calculator 2026

ISO vs NSO: what actually happens the day you exercise

Both option types let you buy shares at a fixed strike price. The tax treatment on the exercise date is where they split apart, and the gap can be tens of thousands of dollars on the same grant.

A non-qualified stock option is the simpler one. The spread between the fair market value and your strike price is ordinary compensation income the moment you exercise (26 U.S.C. Section 83(a), Treas. Reg. Section 1.83-7). It goes into box 1 of your W-2 and stacks on top of the rest of your salary for bracket purposes. Social Security and Medicare apply to it like any other wage. Your employer withholds at the flat 22% supplemental rate, which is frequently below the rate that spread is actually taxed at once it lands on your return.

An incentive stock option produces nothing at all on the regular return. Section 421(a)(1) says no income is recognized when you exercise and hold. Nothing goes on your W-2, and no payroll tax applies. What does happen is that the same spread becomes an alternative minimum tax preference item on Form 6251 under Section 56(b)(3). If that preference lifts your tentative minimum tax above your regular tax, the difference is real cash due in April, even though you sold nothing.

The important part: an ISO defers tax, it does not delete it. The cheaper option at exercise is not always the cheaper option once you sell. AMT paid on an ISO spread usually comes back as a minimum tax credit, and clearing the holding periods turns the whole gain into long-term capital gain. The NSO bill is larger up front but final.

How the ISO bargain element turns into an AMT bill

The calculator runs the Form 6251 comparison in six steps. First the spread: fair market value minus strike price, times shares, floored at zero. Second, AMTI: your other ordinary income plus the spread. The standard deduction is not allowed under AMT (Section 56(b)(1)(E)), so AMTI starts from income rather than from regular taxable income.

Third, the exemption. Take the base exemption for your filing status and subtract 50 cents for every dollar of AMTI above your phase-out threshold, floored at zero. Fourth, the AMT base is AMTI minus that exemption. Fifth, the tentative minimum tax applies 26% to the base up to $244,500 ($122,250 if married filing separately) and 28% to the rest. Sixth, compare the tentative minimum tax to your regular tax. Only the excess is AMT, and it can never go below zero.

Because the regular tax is the comparison figure, a modest spread sitting on a high salary often produces no AMT at all. The regular bill is already above the tentative minimum, so the preference gets absorbed. The break point moves quickly once the exemption starts phasing out, which is why the last few thousand shares in a large exercise usually cost far more per share than the first few thousand.

What OBBB changed for 2026 exercises

Section 70107 of the One Big Beautiful Bill Act (P.L. 119-21) made the higher TCJA exemption amounts permanent, then made the phase-out considerably harsher in two ways that both begin in tax year 2026.

It reset the phase-out thresholds to their original 2018 levels of $500,000 and $1,000,000, well below where inflation indexing had carried them. And it doubled the phase-out rate: the exemption now falls 50 cents per dollar of AMTI above the threshold, up from 25 cents. Together those two changes wipe out the exemption over a $180,200 band for single filers instead of a band twice as wide.

The practical effect lands squarely on a big ISO exercise stacked on a high salary. Every dollar of spread above the threshold costs you 26 or 28 cents of AMT on the dollar itself plus another 13 or 14 cents from the exemption it erases, a marginal rate near 40% in the phase-out band. The number of shares you can exercise before AMT starts is lower in 2026 than it was in prior years, and the answer changes with your salary, so it is worth running the number before you commit rather than after. If you want the full Form 6251 view with SALT and other add-backs included, the AMT Calculator takes it from here.

Holding periods, disqualifying dispositions, and the cash you actually need

ISO treatment survives the sale only if you clear two tests: more than two years from the grant date and more than one year from the exercise date. Clear both and the entire gain above your strike price is long-term capital gain, which you can price with the Capital Gains Tax Calculator. Miss either one and the sale is a disqualifying disposition: the spread measured at exercise converts to ordinary compensation income on your W-2 for the year of the sale, and only the appreciation after exercise stays as capital gain.

That is why the cash question matters as much as the tax question. Exercising an ISO costs you the strike price now plus any AMT next April, with no shares sold to fund either. Exercising an NSO costs you the strike price plus whatever your employer withholds, and the withholding is usually short of the real bill because the 22% supplemental rate rarely matches a high earner's marginal rate. The gap card above shows exactly how much is left over for filing time.

Two taxes are deliberately outside this calculator so the two columns stay directly comparable: state income tax and the 3.8% Net Investment Income Tax, which you can add with the NIIT Calculator. If your equity comes through a purchase plan rather than options, the ESPP Tax Calculator handles the qualifying and disqualifying split for Section 423 shares. To see any of this next to your credits, deductions, and refund, download Tax47. Everything here is an estimate for planning, not tax or legal advice.