ISO vs NSO Tax Comparison Calculator 2026

How ISOs and NSOs Differ at Exercise

Non-Qualified Stock Options (NSOs) are taxed at exercise as ordinary income on the spread between fair market value (FMV) and strike price. The employer withholds federal income tax, FICA, and Medicare on this spread, reported on Form W-2. Incentive Stock Options (ISOs) get preferential treatment: no regular federal income tax at exercise, but the bargain element is an AMT preference item. If you exercise ISOs and hold the stock across calendar year-end without selling, AMT may apply at 26% or 28% on the spread. The 2026 AMT exemption is $88,100 single / $137,000 MFJ (subject to OBBB-driven IRS clarification), phasing out at $626,350 / $1,252,700. AMT paid on ISO exercise creates a future AMT credit that can offset regular tax in later years. Source: IRS Form 3921 (ISO Exercise) and Form 6251 AMT.

Qualifying Disposition vs Disqualifying Disposition

An ISO qualifying disposition requires holding the shares for at least 2 years from grant date AND 1 year from exercise date. When both holding periods are met, the entire gain (sale price minus strike) is taxed as long-term capital gains at federal rates of 0%, 15%, or 20% depending on taxable income — plus 3.8% Net Investment Income Tax above $200K single / $250K MFJ. A disqualifying disposition (sale before either holding period) loses ISO treatment: the spread at exercise becomes ordinary income (W-2 Box 1, no FICA), and only post-exercise appreciation is capital gain. The IRS taxes the spread at sale price minus strike if you sell within the same calendar year as exercise — limiting your downside if the stock falls. NSOs have no qualifying period — you always pay ordinary income on the spread, then capital gains on appreciation after exercise. Source: IRS Publication 525, Taxable and Nontaxable Income.

State Tax and FICA Differences

NSO exercise spreads are subject to FICA (Social Security 6.2% up to $176,100 wage base in 2026, Medicare 1.45% on all, plus 0.9% additional Medicare above $200K single / $250K MFJ). ISO exercise is FICA-exempt — saving 7.65%-8.55% versus NSOs. State income tax treatment varies: California treats ISO AMT as fully taxable (no AMT for state, but CA AMT applies at 7%), New York mirrors federal AMT, and Texas/Florida have no state income tax. If you exercise ISOs in California and later move to Texas before selling, California retains taxing rights on the spread earned while a California resident under the "source" rule. Source: CA Form 3805P (AMT).

$100,000 ISO Annual Limit and 83(b) Election

Only the first $100,000 in fair market value of ISOs (measured at grant) can become exercisable in any one calendar year — excess is automatically treated as NSO. For early-exercise ISOs, file an 83(b) election within 30 days of exercise to start the holding-period clock on unvested shares and lock in the bargain element at the (likely low) early-exercise FMV. Missing the 83(b) deadline means each tranche of vesting shares is a separate exercise event for AMT purposes — potentially blowing past your AMT exemption. The OBBB did not change ISO rules, but the 2026 AMT exemption increase ($85,700 → $88,100 single) gives more room before AMT kicks in. See our AMT Calculator 2026 for a full AMT projection. Last updated May 2026.