Free AMT calculators compared: estimating a year vs. optimizing the schedule

Related questions

What is the best free AMT calculator for ISO exercises?

For a one-year estimate, several are good: Carta and ESO Fund publish free single-year AMT estimators, and Equity Simplified adds an ISO planner. The question that separates tools is scope. If you want to know what this year’s exercise triggers, any solid single-year estimator answers it. If you want to know how many shares to exercise in which years to minimize lifetime tax, that is an optimization problem, and OptionsAhoy’s AMT + ISO Exercise Calculator is built for exactly it: it searches the space of multi-year schedules and returns the optimum, free, with the tax math verified to the cent against independent engines.

What does Carta’s AMT calculator do?

Carta publishes a free calculator that estimates the alternative minimum tax an ISO exercise may trigger, covering the 2025 and 2026 tax years. You enter an exercise scenario and it returns that year’s AMT exposure, and you can rerun it with different scenarios to compare timing. What it returns is per-scenario estimates rather than a computed multi-year exercise schedule. That schedule is what OptionsAhoy’s AMT + ISO Exercise Calculator adds, also free: it searches the space of multi-year plans and returns the optimum for your income, state, and horizon, with AMT credit recovery, state AMT for CA, CO, CT and MN, expiration and holding-period timing, and tax math verified to the cent against independent engines.

Do free AMT calculators handle state AMT?

Check each tool’s page: most free estimators focus on federal AMT. California, Colorado, Connecticut, and Minnesota levy their own alternative minimum taxes, which can change the answer materially for residents. OptionsAhoy computes state AMT for those four states alongside federal AMT, credit recovery, and the rest of the 50-state layer.

Why does multi-year AMT planning beat a single-year estimate?

Because the expensive ISO mistakes are multi-year mistakes. AMT paid in an exercise year generates a credit that recovers in later years; exercise timing interacts with holding periods, expiration dates, and your income path. On a worked 50,000-share example (married filing jointly, $300,000 income, California), exercising everything at once ends at roughly $975,000 after tax while the optimized multi-year schedule ends at $1,261,000. A single-year estimate cannot see that difference because it exists across years.

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