RSU and Stock Option Tax Calculator

Introduction

Restricted stock units and employee stock options can create tax at different moments from the moment cash arrives. RSUs usually create wage income when shares vest. Nonstatutory stock options usually create wage income when the option is exercised. Incentive stock options can avoid regular income at exercise, but the spread can still matter for alternative minimum tax.

Equity award tax planning is useful before a vest, exercise, or sale because the headline share value is not the same as spendable cash. The same grant can involve ordinary income, capital gain or loss, payroll tax, supplemental wage withholding, AMT preference, Net Investment Income Tax, exercise cost, transaction fees, and a possible sell-to-cover decision.

Holding period and award type decide much of the treatment. A same-day RSU sale may be mostly wage income with little capital gain. A held ISO can show no regular wage income at exercise and still create an AMT adjustment. A sale below the vest or exercise value can show a capital loss, but that loss does not automatically solve the tax already created by vesting or exercise.

Use an equity tax estimate as a planning check before selling shares, reserving cash, or changing payroll withholding. Filing positions still need the grant agreement, vesting records, Form W-2, Form 3921 for ISOs, brokerage tax forms, and state-specific rules.

How to Use This Tool:

Start with the equity event you are trying to model, then enter the share, price, income, and withholding assumptions for that same event.

1. Choose Equity event. Use RSU vest and sale for shares that vest as wage income, NSO exercise and sale for nonstatutory options, or one of the ISO modes for an exercise held past year-end, a disqualifying sale, or a qualifying sale.
2. Select Tax year and Filing status. These control ordinary income brackets, long-term capital-gain bands, AMT settings, NIIT thresholds, Additional Medicare thresholds, and the Social Security wage base used in the estimate.
3. Enter Shares vesting or exercised, FMV at vest or exercise, and, for options, Strike price. For RSUs, FMV drives wage income and basis. For options, the spread between FMV and strike price drives NSO wage income or ISO AMT preference.
4. If the event includes a sale, enter Shares sold in this scenario, Sale price, and, for RSU or NSO sales, Sale gain treatment. Keep shares sold at or below the shares vested or exercised, and use long-term treatment only when the holding period supports it.
5. Add Other taxable income before this event and YTD Social Security wages before event. Taxable income affects bracket stacking, NIIT, and AMT. YTD Social Security wages decide how much of the wage income still falls below the wage base.
6. Set Federal withholding on wage income. The automatic supplemental wage setting applies 22% below the $1 million supplemental wage threshold and 37% above it. Use a custom rate when payroll or the equity platform shows a different federal withholding method.
7. Open Advanced for prior supplemental wages, state or local planning rates, state wage withholding, transaction fees, NIIT, and display currency. Then review Equity Tax Summary, Award Tax Ledger, ISO AMT Watchlist, Review Notes, Tax Mix, and Sale Price Curve.

If Review Notes flags an out-of-the-money option, ISO AMT adjustment, capital loss, high supplemental withholding portion, or ISO holding-period issue, resolve that fact before using the tax gap or net cash number for a trade or estimated tax payment.

Interpreting Results:

Total tax estimate is the modeled tax cost of the event. It can include federal ordinary income tax, long-term capital-gains tax, employee payroll taxes, optional state/local tax, NIIT, and ISO AMT exposure. It is not the same as withholding, and it is not a full tax return calculation.

Tax gap after withholding is the main cash-planning signal. A positive value means the modeled tax exceeds federal wage withholding, employee payroll withholding, and entered state withholding. A negative value means the event has a modeled withholding cushion, not a guaranteed refund.

Read the ISO AMT Watchlist and Review Notes with the headline number. A clean net cash result can still be unreliable if the ISO holding period, state tax rate, other taxable income, YTD wages, or source year is wrong.

Technical Details:

Equity compensation tax starts by classifying the event. RSU vesting and NSO exercise can create compensation income before a later sale is considered. ISO exercise has a separate regular-tax and AMT pattern: regular tax often waits until sale, while AMT can include the exercise spread when shares are still held after year-end.

The sale calculation then compares sale price with the basis created by that event. RSUs and NSOs usually use FMV at vest or exercise as regular basis. A qualifying ISO sale uses strike price as regular basis. A disqualifying ISO sale can split value between ordinary income and capital gain, with ordinary income limited by the exercise spread and the sale-price-over-strike amount.

The core cash result combines the tax layers with sale proceeds, exercise cost, and withholding. The formula below uses positive capital gain for capital-gain taxes and NIIT; a capital loss is shown in the output but is not used to create a capital-loss deduction inside this single-event estimate.

Federal ordinary income tax is incremental. The estimate calculates tax on other taxable income plus equity ordinary income and short-term gain, then subtracts tax on other taxable income alone. Long-term capital gain is stacked above ordinary taxable income and allocated through the 0%, 15%, and 20% long-term capital-gain bands for the selected filing status.

Payroll and withholding are separate from final income tax. RSU and NSO compensation can be subject to employee Social Security, Medicare, and Additional Medicare tax. Federal supplemental withholding is a credit against tax, not the final tax itself, so a 22% withheld RSU vest can still leave a tax gap when the taxpayer's incremental federal, payroll, state, and investment-income taxes are higher.

The ISO AMT estimate is deliberately narrow. The AMT preference starts with the ISO spread on shares still held after year-end. Tentative AMT is estimated using other taxable income plus that preference, then compared with regular tax on other taxable income. The method can flag exposure from the ISO exercise, but it does not rebuild Form 6251 with every AMT adjustment, credit, exemption interaction, or future AMT credit carryforward.

Limitations, Privacy, and Accuracy:

Treat the result as an educational planning estimate for a single U.S. equity event, not tax, legal, investment, payroll, or filing advice.

• The estimate does not model multi-lot vest schedules, grant-date ISO holding-period validation, section 83(b) elections, ESPP rules, wash sales, capital-loss carryovers, AMT credit carryforward, itemized deductions, credits, or state-specific tax law.
• Federal source values were reviewed against official guidance on 2026-05-16. Tax authorities, payroll guidance, forms, and state rules can change after a calculator is built.
• Flat state/local rates are manual planning inputs. They do not replace state withholding tables, sourcing rules, residency rules, local taxes, or special treatment for equity compensation.
• The calculation does not require brokerage credentials or grant-platform access. Copied rows, chart data, downloaded tables, and JSON can still contain sensitive income, price, and award assumptions if you store or share them.

Before exercising options, selling shares, making estimated tax payments, or changing payroll withholding, compare the output with official forms, employer payroll records, brokerage statements, and a qualified tax adviser.

Worked Examples:

RSU vest with a same-day sale

With 500 RSU shares vesting at a $42 FMV and sold at $48, the event creates Ordinary wage income of $21,000 and a Capital gain or loss of $3,000. Using 2026 single filing status, $165,000 of other taxable income, $140,000 of YTD Social Security wages, 5% state planning rates, and automatic supplemental withholding, the output shows Total tax estimate of $8,716.50, Withholding credits of $7,276.50, and a Tax gap after withholding of +$1,440.00. The Net cash after tax estimate is $15,258.50 after the modeled tax and $25 fee.

NSO exercise with only part of the shares sold

A 1,000-share NSO exercise at $28 FMV with a $6 strike creates a $22 spread per share, so Ordinary wage income is $22,000. If only 400 shares are sold at $31, the sale proceeds do not fully cover exercise cost, fees, and tax. With $190,000 of other taxable income and 7% state planning rates, the estimate shows Total tax estimate of $9,873.00, Tax gap after withholding of +$2,250.00, and Net cash after tax of -$3,498.00. That negative cash result is a funding warning, not a final tax bill.

ISO exercise held past year-end

Exercising 1,000 ISOs at a $6 strike when FMV is $28 creates no modeled regular wage income in the ISO hold mode, but it creates a ISO AMT preference of $22,000. With the same $190,000 of other taxable income, the sample estimate shows AMT exposure estimate of $0.00 because the preference does not create modeled AMT above the regular-tax comparison. The Cash needed after withholding still shows $6,025.00 because the exercise cost and fee have to be funded even when no tax is modeled.

A troubleshooting pattern appears when the Review Notes list reports a capital loss or an ISO qualification issue. A sale below basis can reduce the Capital gain or loss field, but the calculator does not apply capital-loss deduction limits or wash-sale rules. Fix the lot, holding period, and Form 3921 facts before treating the result as a tax-payment plan.

FAQ:

Glossary:

RSU

Restricted stock unit, usually taxed as wage income when shares vest and become available.

NSO

Nonstatutory stock option, usually taxed at exercise on the spread between FMV and strike price.

ISO

Incentive stock option, a statutory option type that can avoid regular income at exercise but can create AMT preference.

FMV

Fair market value per share at vesting or exercise, used for RSU income, option spread, and basis calculations.

AMT preference

An adjustment that can increase alternative minimum taxable income, such as the ISO exercise spread on shares held past year-end.

NIIT

Net Investment Income Tax, a 3.8% tax that can apply to investment gain when modified adjusted gross income exceeds the threshold.

Supplemental wage withholding

Federal wage withholding method often used for bonuses, RSU income, and option compensation outside regular payroll.

Tax gap

The modeled difference between total estimated tax and withholding credits for the event.

References:

• Topic no. 427, Stock options, Internal Revenue Service, updated 28 Apr 2026.
• Publication 15 (2026), Employer's Tax Guide, Internal Revenue Service, 2026.
• Instructions for Form 6251 (2025), Internal Revenue Service.
• Rev. Proc. 2025-32, Internal Revenue Service, 2025.
• Contribution and Benefit Base, Social Security Administration.
• Topic no. 559, Net investment income tax, Internal Revenue Service.
• Topic no. 560, Additional Medicare tax, Internal Revenue Service, updated 22 Jan 2026.