Start with Form 3921
Box 3 reports the exercise price per share, box 4 reports fair market value per share on the exercise date, and box 5 reports the number of shares transferred.
FREE ISO & AMT PLANNING WORKSHEET
ISO AMT calculator: estimate the exercise spread, not the final tax
Use the exercise price, fair market value, and share count from Form 3921 to estimate exercise cost, stock value, and the spread that may enter the alternative minimum tax calculation.
No sign-upFigures stay in your browserNot an investment recommendation
FORM 3921 WORKSHEET
Estimate the ISO exercise spread before completing Form 6251
Enter one exercise at a time. Use general planning figures only; do not enter Social Security numbers, account numbers, employer identifiers, or documents.
Private by design: calculations happen in this browser. The figures you enter are not included in analytics events or saved by this tool.
Spread only—not your AMT.
This tool does not calculate AMT due, determine whether you owe AMT, prepare Form 6251, or address state tax. Do not treat the spread as a tax adjustment when shares were restricted, any shares were disposed of during the exercise year, or the award's ISO status is uncertain.
WHAT THE WORKSHEET CALCULATES
The spread is one input—not the amount of AMT owed
Calculate the exercise spread
The basic spread is the excess of fair market value over the exercise price, multiplied by the applicable shares. If fair market value does not exceed the exercise price, this worksheet shows a zero positive spread.
Complete the rest of Form 6251
Whether additional AMT is actually due depends on the complete return, including other income, deductions, filing status, exemption rules, credits, and prior adjustments.
IMPORTANT LIMITS
What this calculator does not determine
This worksheet estimates a simple exercise spread. It does not prepare Form 6251, calculate tentative minimum tax, or tell you whether to exercise, hold, or sell company stock.
- Final regular tax, alternative minimum tax, estimated payments, or state tax
- Special timing when stock rights are not transferable or remain subject to a substantial risk of forfeiture
- Same-year sale reporting, disqualifying dispositions, multiple grants, or partial-lot identification
- Regular-tax basis, AMT basis, a later sale, or the minimum-tax credit
- Option qualification, employment-status rules, Section 83(b), or legal restrictions
- Stock value, liquidity, concentration risk, or an investment recommendation
PRIMARY IRS GUIDANCE
Sources and review date
Rules and links reviewed July 24, 2026. Recheck the current IRS forms and instructions for the exercise year.