ISO AMT Calculator
Model potential AMT from ISO exercises — many inputs may require manual entry depending on your situation.
You are modeling ISO exercise before you click exercise — this calculator estimates AMT on the spread. It is not a substitute for Form 6251 or a CPA.
Gather before you start
- Grant agreement confirming status and strike price.
- Current 409A or your company uses for exercise.
- Number of shares you plan to exercise.
- Prior-year tax return for context (if available).
- Cash plan for tax due even if you do not sell shares.
AMT modeling only. ISO qualification rules and state conformity vary.
In plain terms
Planning estimate
AMT is genuinely complex and depends on your full tax return. This tool shows the ISO spread (the AMT preference) and an optional rough estimate from rates you enter. It is not a Form 6251 calculation or tax advice.
We do not pre-fill personal financial values. Estimates appear only after you enter your own numbers.
Enter your details to estimate
Add your equity, income, state, and withholding details to see an educational estimate. No personal financial values are pre-filled.
Start with the fields below.
Your details
Enter your own numbers below. This is an estimate, not a filing position.
Required to estimate
Required to estimate
Fair market value (e.g. 409A or market price) when you exercise.
Required to estimate
Rough total of your other income, used only for the simplified AMT income figure.
Not loaded in config. Enter your AMT exemption to see a rough estimate; leave blank to skip.
Not loaded in config. Enter an AMT rate to see a rough estimate; leave at zero to skip.
Results will appear here once you enter the required details on the left.
Related guides
- ISO AMT Explained
AMT can make an ISO exercise expensive in cash even before you sell shares — understand the spread first.
- How ISOs Are Taxed
ISO tax is a sequence: usually no tax at grant, possible AMT at exercise, capital gain treatment on qualifying sales.
- ISO vs NSO Tax Difference
ISOs and NSOs are taxed differently — the exercise and sale timeline drives most of the difference.
- Stock Options vs RSUs
Options and RSUs follow different tax paths — know which events create wage income vs capital gain.
When to use this calculator
- You plan to exercise incentive stock options () and hold shares rather than sell immediately.
- You want a planning estimate of alternative minimum tax on the spread at exercise before committing cash.
- You exercised in a year with other preference items and need a rough combined picture.
Inputs you need
- Number of exercising, strike price, and current (409A for private companies).
- Filing status, tax year, and other rough preference income if you know it.
- Whether you expect to sell within holding periods (affects later vs — not fully modeled here).
How to interpret the result
- Output estimates on the spread at exercise — cash you may owe even without selling shares.
- Compare to regular tax estimate shown alongside; the higher of the two frameworks drives what you may need to set aside.
- paid on spread may generate a minimum tax credit in later years — carryforward rules are complex and not calculated here.
What this calculator does not know
- Full Form 6251 calculation: exemptions phaseouts, other preferences, state conformity.
- Whether your exercise qualifies for treatment (employment status, plan rules, 90-day post-termination windows).
- Disqualifying dispositions within two years of grant or one year of exercise.
- Liquidity to pay without selling shares — a cash-flow question, not a tax-rate question.
Documents to verify before filing
- Stock option grant agreement ( vs , strike, expiration).
- Exercise confirmation and Form 3921 after year-end for exercises.
- Company 409A or board valuation used at exercise (private shares).
- Prior Form 6251 if you paid before.
Next pages to read
These links are for education and planning. They are not filing instructions and do not replace review of your own documents or a qualified tax professional.
How the tax works
exercises may avoid regular wage tax but the spread can be an preference item.
is a parallel tax system — you may owe tax without selling stock.
Qualifying dispositions later can affect how much was prepaid via credits.
What to check on your end
- Spread per share ( minus strike) times shares exercised.
- Whether you are already in territory from other preferences.
- Cash needed to pay vs. waiting for a liquidity event.
- Post-exercise holding periods for qualifying sale treatment.
Exercising ISOs without modeling AMT cash
What to pull from your files
- Form 3921 after exercise (spread reporting).
- Exercise confirmation from equity portal.
- Company 409A or board valuation memo.
- Prior Form 6251 if you paid before.
Example scenario (hypothetical)
Illustration only, not your tax situation.
Questions people ask
- What is ISO exercise tax?
- Often on the spread in the year you exercise, even if you do not sell. exercises, by contrast, usually create wage income at exercise with employer .
- How much AMT on ISO exercise?
- Depends on spread ( minus strike) × shares, your other income, and full rules. This calculator gives a planning estimate — not Form 6251.
- Does this replace Form 6251?
- No. It is a planning estimate. Your actual depends on full return details, exemptions, and other preference items.
- What if I also have NSOs?
- spread is usually wage income, not . Model separately — stacking both in one year changes and brackets.
When a CPA is worth it
- You exercise a large grant while private.
- You may disqualifyingly dispose of shares within two years of grant.
- You paid before and want to understand credit carryforward.
Sources and notes
Primary tax claims on this page are supported by the official and secondary sources below. Broker and software links describe reporting mechanics — confirm rules against IRS or state guidance.
ISO exercise spread as AMT preference item.
- IRS Topic 427 — Stock options
Internal Revenue Service · Official
Overview of statutory (ISO, ESPP) vs nonstatutory options, exercise timing, and Form 3921/3922 reporting.
- Instructions for Form 6251 — Alternative Minimum Tax
Internal Revenue Service · Official
AMT treatment of ISO exercise spread and related adjustments.
Related calculators
Related pages
- ISO AMT Explained
AMT can make an ISO exercise expensive in cash even before you sell shares — understand the spread first.
- How ISOs Are Taxed
ISO tax is a sequence: usually no tax at grant, possible AMT at exercise, capital gain treatment on qualifying sales.
- ISO Exercise Tax Calculator Guide
A short guide to our ISO AMT calculator: what it estimates, what it cannot, and what to gather first.
For learning, not filing
VestingTax.com is not a CPA firm or tax preparer. Grants, employers, and states all differ. Use the cited IRS and state sources above, your own documents, and a qualified tax professional before you make decisions from this guide.