NSO vs ISO Exercise Order: $200K Spread Math

For tech employees who hold both NSOs and ISOs — common at later-stage private companies, at public companies after a partial conversion, or simply because of the $100K ISO cap forcing the excess to NSO treatment — the exercise-order question matters more than most planners realize. The interaction between IRC §83 (NSO ordinary income at exercise) and IRC §56(b)(3) (ISO AMT preference) creates an asymmetric tax structure where the same dollar amounts in different orders produce different total tax outcomes.

The headline rule: exercise NSOs before ISOs in the same calendar year. The NSO exercise raises regular income tax, which absorbs the AMT exposure from a subsequent ISO exercise. The reverse order forfeits this absorption and produces unnecessary AMT.

The mechanic: why NSO ordinary income absorbs ISO AMT

The AMT calculation under IRC §55 compares two tax computations in the same year:

• Regular tax: ordinary income taxed at progressive marginal brackets (10%-37% federal in 2026)
• Tentative minimum tax (TMT): AMTI minus AMT exemption, multiplied by 26% (or 28% above the bracket break)

You pay the higher of regular tax or TMT. AMT is the excess of TMT over regular tax.

NSO exercise produces ordinary income under IRC §83(a). This income:

• Increases regular taxable income, raising regular tax owed
• Is also included in AMTI (because AMTI starts from regular taxable income and adds preferences)
• Therefore raises both regular tax AND TMT by approximately the same amount (the difference depends on marginal rates)

ISO exercise (without sale in same year) produces no regular income but adds the spread to AMTI as a preference under IRC §56(b)(3). This:

• Does NOT raise regular tax
• Raises TMT by the spread × 26% or 28%
• Creates AMT exposure equal to the TMT increase

When both exercises happen in the same calendar year:

• Regular tax goes up by the NSO ordinary income at the marginal regular bracket (typically 32%-37%)
• TMT goes up by both the NSO income AND the ISO spread at 26%-28%
• The regular tax increase is OFTEN LARGER than the TMT increase from the NSO alone, so the NSO absorbs some or all of the ISO AMT exposure

Worked example: $100K NSO + $100K ISO, single filer at 32% bracket

Maria is a software engineer in Austin (no state income tax). $200K W-2 salary. She holds 5,000 NSOs (FMV $30, exercise price $10, spread $20/share = $100K total) and 5,000 ISOs (same spread, $100K). She wants to exercise both in 2026.

Scenario A: Exercise NSO first, ISO second (same year)

Regular tax:

• W-2 income: $200,000
• NSO exercise ordinary income: $100,000
• Total W-2 + NSO: $300,000
• Standard deduction (single 2026): $15,750
• Regular taxable income: $284,250
• Regular federal tax: ~$70,300 (bracket-by-bracket: 10% × $11,925 + 12% × $36,550 + 22% × $54,875 + 24% × $93,950 + 32% × $53,225 + 35% × $33,725)

AMT calculation (ISO held past December 31):

• Regular taxable income: $284,250
• + ISO spread (AMT preference): $100,000
• + Standard deduction add-back: $15,750
• AMTI: $400,000
• - AMT exemption ($88,100 single): ($88,100)
• AMT taxable income: $311,900
• TMT: 26% × $239,100 + 28% × $72,800 = $62,166 + $20,384 = $82,550

AMT owed: $82,550 (TMT) - $70,300 (regular tax) = $12,250

Scenario B: Exercise ISO first, no NSO this year

Regular tax:

• W-2 income: $200,000
• Standard deduction: $15,750
• Regular taxable income: $184,250
• Regular federal tax: ~$36,800

AMT calculation:

• Regular taxable income: $184,250
• + ISO spread: $100,000
• + Standard deduction add-back: $15,750
• AMTI: $300,000
• - AMT exemption: ($88,100)
• AMT taxable income: $211,900
• TMT: 26% × $211,900 = $55,094

AMT owed: $55,094 - $36,800 = $18,294

Scenario C: Exercise ISO first, NSO second in same year

Same total income and AMTI as Scenario A (order within a year doesn't change the year-end calculation). AMT owed: $12,250. Same as Scenario A.

Key insight: within a single calendar year, the order of exercise doesn't matter mathematically — both ISO and NSO contribute to the same year-end AMTI calculation. The order matters when the exercises are split across multiple years.

Scenario D: Exercise ISO in Year 1, NSO in Year 2

Year 1: ISO exercised, no NSO. As Scenario B: AMT owed $18,294.

Year 2: NSO exercised, no ISO. Ordinary income tax on $100K spread at 32% marginal = $32,000 federal + FICA + state. No AMT.

Total tax across both years: $18,294 (Year 1 AMT) + $32,000 (Year 2 NSO) + Year 1 regular tax $36,800 + Year 2 regular tax $36,800 = $123,894 over two years.

Scenario E: Exercise NSO in Year 1, ISO in Year 2

Year 1: NSO exercised, no ISO. Ordinary income on $100K: $32,000 federal + FICA. Regular tax on full income ($300K) = $70,300. No AMT.

Year 2: ISO exercised, no NSO. As Scenario B: AMT owed $18,294. Regular tax = $36,800.

Total tax: Year 1 $70,300 + Year 2 ($36,800 regular + $18,294 AMT) = $125,394 over two years.

Net difference: Scenario D (ISO first) costs $123,894; Scenario E (NSO first across years) costs $125,394. The NSO-first across years is slightly worse by $1,500 because the ISO Year 2 still triggers some AMT.

Scenario F: Both exercises in Year 1 (NSO + ISO combined)

As Scenario A: AMT owed $12,250 federal + Regular tax $70,300 = $82,550. Plus Year 2 regular tax on baseline W-2 only = $36,800.

Total tax: $82,550 + $36,800 = $119,350 over two years.

The cross-year comparison reveals the actual optimal

For Maria's specific scenario ($200K W-2, single, $100K NSO + $100K ISO), the optimal is both exercises in Year 1 — the NSO ordinary income absorbs $6K of the ISO AMT that would otherwise be owed. Scenario F beats Scenario D by $4,544 in federal tax.

The key takeaway: the same-year combined exercise produces a better outcome than splitting across years when the NSO is large enough to materially raise regular tax above TMT for the ISO portion.

When NSO-first within the same year matters

Within a single calendar year, the order of NSO and ISO exercise does not change the year-end tax calculation — the AMTI is computed once at year-end regardless of when within the year the underlying events occurred. The mathematical result is identical.

Order matters for practical reasons within the year:

• Withholding management: NSO exercise generates federal income tax withholding (at the 22%/37% supplemental rates) and FICA wages. Doing NSO early in the year means withholding is captured against the year's tax obligation before the AMT cash crunch hits.
• Estimated tax planning: the under-withholding shortfall on a large NSO (where 22% supplemental under-covers the 32% bracket) can be addressed via Q1-Q4 estimated payments. ISO AMT is generally not addressed via withholding; it shows up at April 15.
• Stock price risk during the year: NSO exercise can be done as same-day sale (avoiding all subsequent stock risk on the NSO portion). ISO exercise typically requires holding for qualifying disposition, so the timing of NSO sale doesn't affect ISO holding period.
• 10b5-1 plan sequencing: for insider-restricted employees, the 10b5-1 plan schedule must accommodate both exercises. Typical sequence: NSO exercise + same-day sale in Q1 (when 10b5-1 plan first executes), ISO exercise + hold in Q2-Q3 (after NSO sale has cleared but within the qualifying disposition window).

When NSO-first across years matters

Cross-year sequencing matters most when the employee's W-2 income is low enough that the AMT exemption would absorb the ISO spread alone. In that case, Year 1 NSO followed by Year 2 ISO can produce zero AMT in both years.

Worked example: $100K W-2, $100K NSO + $100K ISO

David is a more junior engineer, single, $100K W-2 in Austin. Same 5,000 NSO + 5,000 ISO grants ($100K spread each).

Scenario F (both Year 1):

• Regular tax: W-2 $100K + NSO $100K = $200K total, taxable $184K, regular tax ~$36,800
• AMTI: $184K + $100K (ISO) + $15.75K (SD add-back) = $299,750
• AMTI - exemption: $211,650
• TMT: 26% × $211,650 = $55,029
• AMT owed: $55,029 - $36,800 = $18,229
• Total Year 1: $55,029

Scenario E (NSO Year 1, ISO Year 2):

• Year 1: W-2 $100K + NSO $100K = $200K, regular tax $36,800, no AMT. Total Year 1: $36,800.
• Year 2: W-2 $100K only, NSO already exercised in Year 1. Regular tax ~$13,400. AMTI: $100K + $100K ISO + $15.75K SD add-back = $215,750. AMTI - exemption $88.1K = $127,650. TMT: 26% × $127,650 = $33,189. AMT owed: $33,189 - $13,400 = $19,789. Total Year 2: $33,189.
• Total over 2 years: $36,800 + $33,189 = $69,989.

Compare: Scenario F (both Year 1) total = $55,029 + Year 2 baseline $13,400 = $68,429.

Scenario F still wins by ~$1,560. The NSO absorbing the ISO AMT in the same year produces a slightly better outcome than splitting.

Where cross-year wins: very low income

If David's W-2 were $60K (mid-career career-change, part-time consulting), splitting NSO and ISO across years could produce $0 AMT in both years — potentially saving $5K-$10K vs combining both in one year.

Scenario E with $60K W-2:

• Year 1: W-2 $60K + NSO $100K = $160K, regular tax ~$23,600. AMTI without ISO: $160K + $15.75K = $175.75K. AMTI - exemption: $87,650. TMT: 26% × $87,650 = $22,789. Regular tax exceeds TMT by $811. AMT: $0.
• Year 2: W-2 $60K only. Regular tax ~$5,400. AMTI: $60K + $100K ISO + $15.75K = $175,750. AMTI - exemption: $87,650. TMT: 26% × $87,650 = $22,789. AMT owed: $22,789 - $5,400 = $17,389.
• Total over 2 years: $23,600 + $22,789 = $46,389.

Scenario F with $60K W-2 (both Year 1):

• Regular tax: W-2 $60K + NSO $100K = $160K, regular tax $23,600
• AMTI: $160K + $100K + $15.75K = $275.75K. AMTI - exemption: $187.65K. TMT: 26% × $187.65K = $48,789.
• AMT owed: $48,789 - $23,600 = $25,189.
• Total Year 1: $48,789 + Year 2 baseline $5,400 = $54,189.

At $60K W-2, splitting across years (Scenario E) costs $46,389 vs combining in one year (Scenario F) at $54,189 — $7,800 of savings from the cross-year split.

The pattern: at low W-2 income where each year's AMT exemption can absorb a meaningful portion of the spread independently, splitting NSO and ISO across years lets both exemptions be used. At higher W-2 income where each year's exemption is consumed by base income alone, combining in one year (with NSO ordinary income absorbing ISO AMT) wins.

The $100K ISO cap and forced NSO conversion

Under IRC §422(d), ISOs that would result in more than $100,000 of fair market value (at grant date) becoming exercisable for the first time in a single calendar year are automatically treated as NSOs for the excess. The cap is per-employee per-year and applies based on the FMV at grant, not at vest.

This rule creates mixed NSO+ISO situations involuntarily:

• Employee receives a single grant of options with $400K of FMV vesting in Year 1.
• Under §422(d), only $100K of FMV stays ISO-treated; the other $300K is treated as NSO.
• The employee now has $100K of ISOs + $300K of NSOs from what was supposed to be a single ISO grant.

The $100K cap is computed in the order the options become first exercisable (vesting accelerates the order under §422(d)(3)). For grants with backloaded vesting (e.g., cliff at Year 1 followed by monthly vesting), the cap typically applies to the cliff vest tranche.

Planning implication: employees with grants that exceed the $100K cap should track which portion of each year's vest is ISO-treated and which is NSO-treated. The NSO portion can be exercised earlier (no AMT mechanics) while the ISO portion benefits from the sweet-spot planning and the qualifying disposition path.

State considerations: California vs no-tax states

California's 7% state AMT applies the same NSO-absorption mechanic at the state level. California treats NSO exercise as ordinary income subject to CA state income tax (raising state regular tax) and ISO exercise as a CA AMT preference item. The state-level absorption typically works in parallel with the federal mechanic.

For no-state-tax states (TX, FL, WA, NV, WY, SD, TN, AK, NH), only the federal mechanic applies. The federal NSO-absorbs-ISO-AMT calculation is unchanged.

For high-tax states (NY, NJ, OR, MA), the state AMT (where applicable) and ordinary income tax interactions follow the federal pattern. NY does not have a separate state AMT, so the federal analysis is largely sufficient.

The 90-day post-termination twist

For employees facing termination with vested but unexercised NSOs and ISOs:

• NSOs typically have the same plan-level exercise window as ISOs (often 90 days post-termination, sometimes extended to 5-10 years for departing employees).
• ISOs must be exercised within 90 days post-termination to retain ISO treatment under IRC §422(a)(2). After 90 days, ISOs automatically convert to NSO treatment.
• The NSO-first-within-year sequencing still applies during the 90-day window. Exercise the NSOs first (any time within the plan's permitted window), then exercise the ISOs before the 90-day cliff.
• If the NSO and ISO both have to be exercised in the same calendar year (because of termination timing), the combined-exercise math (Scenario F above) applies.

Common NSO+ISO exercise-order mistakes

• Exercising ISO alone in a low-income year: missing the chance to use the NSO ordinary income to absorb AMT. Common when employee thinks "I'll save AMT by doing the ISO first" — actually the opposite at low income.
• Splitting NSO and ISO across years at high income: at $200K+ W-2, the combined-year exercise typically wins. Splitting forfeits the AMT absorption benefit.
• Forgetting the $100K cap: assuming a grant is all ISO when §422(d) converts the excess to NSO. The planning implications differ for the ISO portion vs the NSO portion.
• Triggering same-day sale on ISOs accidentally: selling ISO shares in the same calendar year as exercise is a disqualifying disposition. The spread becomes ordinary income, not AMT. This is an escape valve when AMT would be onerous but a mistake when the employee intended to hold for qualifying disposition.
• Missing the cross-year planning window: at very low income, splitting can save $5K-$10K. Most planners default to combined-year exercise without modeling the cross-year alternative.
• Ignoring state AMT (California): California's 7% AMT requires the same NSO-first analysis at the state level. The combined federal+state savings from optimal sequencing can be $15K-$30K.

Decision framework: NSO vs ISO exercise sequencing

1. What is my W-2 baseline income (excluding equity exercises)? If $150K+ (single), combine NSO + ISO in one year. If under $80K, consider splitting to use two AMT exemptions.
2. What is the total spread on NSO and ISO? If NSO spread > 1.5x ISO spread, combined-year exercise reliably absorbs the ISO AMT. If NSO is much smaller, the absorption is partial.
3. Is termination imminent (90-day window)? If yes, combine in same calendar year (no choice on cross-year split).
4. Am I in California or another state with state-level AMT? Yes — recalculate with state AMT. The NSO-absorption mechanic still applies but the savings is amplified by state tax.
5. Does my cash flow allow exercising both in one year? NSO exercise costs the exercise price + ordinary tax (withholding partially covers). ISO exercise costs the exercise price + AMT. Combined exercise cash needs may exceed available liquidity, forcing cross-year sequencing.
6. Am I subject to insider trading restrictions? If yes, plan via 10b5-1 with NSO exercise+same-day-sale early in the year and ISO exercise mid-year to align with the qualifying disposition hold period.

Key takeaways

• NSO exercise produces ordinary W-2 income that raises regular federal tax. ISO exercise produces an AMT preference item with no offsetting regular tax. Combining both in the same calendar year often lets the NSO regular tax absorb the ISO AMT exposure.
• On a $100K NSO + $100K ISO at the 32% bracket (single, $200K W-2), combining both in Year 1 produces $12,250 of AMT vs $18,294 if the ISO is exercised alone — a $6,044 federal tax savings from same-year combined exercise.
• Within a single calendar year, the order of exercise (NSO first vs ISO first) doesn't change the year-end tax math. The combined AMTI is computed once. Practical sequencing matters for withholding management and 10b5-1 plan execution.
• Cross-year splitting (NSO Year 1, ISO Year 2 or vice versa) wins at very low W-2 income (under $80K) where each year's AMT exemption can absorb a meaningful portion of the spread independently. Splitting can save $5K-$10K at this income level.
• The $100K ISO cap under IRC §422(d) automatically converts excess ISOs to NSO treatment. Mixed NSO+ISO situations are often involuntary, created by the cap on a single grant.
• California's 7% state AMT amplifies the federal NSO-absorption mechanic. Combined federal+state savings from optimal sequencing can reach $15K-$30K on $200K of total spread.
• For employees facing termination, the 90-day ISO exercise window often forces same-year combined exercise. Exercise NSOs first (any time within the plan's window) and ISOs within the 90-day cliff.
• Mistakes to avoid: exercising ISO alone in a low-income year, splitting NSO+ISO at high income, forgetting the $100K cap conversion, and ignoring state AMT in California.