ISO vs NSO Calculator — Which Stock Option Type Wins After Tax?

ISOs beat NSOs after tax in the most common scenario where (1) you can fund the strike-price exercise out of pocket, (2) you're willing and able to hold the shares for 2 years from grant + 1 year from exercise, (3) you have AMT headroom (AMTI well below the $88,100 single / $137,000 MFJ 2025 exemption phaseout), and (4) the stock is reasonably likely to appreciate. In that case the entire gain from strike to sale is taxed at long-term capital gain rates with no FICA, vs NSOs where the bargain element is taxed as ordinary income + FICA at exercise.

NSOs win when you cannot afford to exercise-and-hold (a same-day cashless exercise sells immediately to fund strike + tax), when AMT exposure on an ISO exercise would be punitive, when the stock is already volatile or peaked, when you do not expect to hold 1 year post-exercise, or when the company is not granting you ISOs anyway (the $100k/year first-exercisable cap matters; excess over $100k is automatically NSO regardless of grant agreement). NSOs are also more flexible — you control the timing and the tax outcome is predictable.

Under IRC §422(d), the aggregate fair market value (measured at grant date) of stock that becomes first-exercisable in any one calendar year for an employee cannot exceed $100,000 of ISO treatment. Any options first-exercisable in that year above $100,000 grant-date FMV are treated as NSOs by operation of law — even if the grant agreement says ISO. Plan vesting schedules cause this trip-wire most often (large initial grants with monthly vesting). Your stock plan administrator should flag the bifurcation when running the exercise.

ISOs do not generate Social Security or Medicare tax at exercise — the bargain element is an AMT preference, not W-2 wages, so there's no FICA event. NSOs trigger 6.2% Social Security (up to the $176,100 2025 wage base) plus 1.45% Medicare on the entire bargain element, plus 0.9% additional Medicare for high earners. On a $200,000 NSO bargain at exercise this can be roughly $14,000+ in FICA on top of federal and state ordinary tax — money you don't pay on an ISO exercise. The ISO trade-off is potential AMT instead.

Generally no. The grant type is fixed at the time of grant per the option agreement. The exception is automatic: any ISOs that exceed the $100k first-exercisable limit in a year are reclassified as NSOs by §422(d). You cannot retroactively change ISO to NSO or NSO to ISO at the employee level. If you have a mix of grants, you can choose which tranches to exercise first (subject to vesting), which gives you some flexibility in tax sequencing.

Yes — at very early-stage startups where FMV equals strike (or close to it), early-exercising both ISOs and NSOs and filing a Section 83(b) election within 30 days zeros the bargain element at grant. For NSOs this means no ordinary income event at vest. For ISOs it means no AMT preference at vest. All future appreciation becomes long-term capital gain (assuming the holding-period clock starts at exercise). The risk is symmetric for both grant types: if shares are forfeited or the stock drops, the tax already paid is not recoverable.

When you select ISO and the holding period is not met, the calculator shows the disqualifying-disposition path: the bargain element becomes ordinary income at sale instead of LTCG, but no FICA applies (it stays §422 stock). When the disqualifying sale happens in the same calendar year as the exercise, AMT does not apply — the regular-tax inclusion replaces the AMT preference. Use the date inputs to model an exercise-and-hold-then-sell early scenario; the calculator surfaces both the qualifying and disqualifying outcomes side-by-side.