RSU and Stock Option Tax Calculator

Introduction

Equity compensation turns one employer award into several tax questions. A restricted stock unit vest can create wages before any shares are sold. A nonstatutory stock option can create compensation income at exercise because the stock is worth more than the strike price. An incentive stock option may avoid regular wage income at exercise, then create alternative minimum tax exposure when the shares are still held after year-end.

The same grant value can leave very different cash outcomes. Award type controls when income starts, sale price controls later gain or loss, and prior wages decide how much Social Security tax room is left. Other taxable income can also push incremental wages into a higher ordinary bracket, move long-term gains through the 0%, 15%, and 20% capital-gain bands, or make positive investment gain subject to Net Investment Income Tax.

Withholding is often mistaken for the final bill. Equity wage income may be withheld at supplemental wage rates that do not match the taxpayer's actual marginal rate. Federal withholding, employee Social Security, Medicare, optional state withholding, and any sell-to-cover shares are payment mechanics. They reduce what may still be due, but they do not prove the tax liability is fully covered.

A good estimate separates the award's value from the cash available to pay tax. RSU shares may be sold automatically to cover withholding, NSO exercises may require cash for the strike price, and ISO exercises may create AMT exposure without a sale. Sale price can help or hurt, but a later capital loss does not automatically erase wage income that was already created at vesting or exercise.

A reliable equity estimate starts with records, not memory. Grant agreements, vesting confirmations, payroll records, Form W-2, Form 3921 for ISOs, brokerage statements, state sourcing rules, and current filing-year thresholds can all change the final return. The practical goal is a tax set-aside and cash-flow check before exercising, selling, or assuming payroll withholding has covered the full bill.

How to Use This Tool:

Model one equity event at a time, using the values that match the vest, exercise, or sale you are planning.

1. Choose Equity event. Use RSU vest and sale for restricted stock units, NSO exercise and sale for nonstatutory stock options, or the ISO modes for an exercise held past year-end, a disqualifying sale, or a qualifying sale.
2. Select Tax year and Filing status. The calculator uses the selected year for federal ordinary income brackets, long-term capital-gain bands, AMT settings, supplemental wage withholding, Medicare thresholds, and the Social Security wage base.
3. Enter Shares vesting or exercised and FMV at vest or exercise. For options, also enter Strike price so the spread can be calculated.
4. If shares are sold in the scenario, fill in Shares sold in this scenario, Sale price, and, when shown, Sale gain treatment. Keep sold shares at or below the shares in the event. 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. These fields affect bracket stacking, NIIT, AMT comparison, Additional Medicare, and the remaining Social Security wage base.
6. Set Federal withholding on wage income. The automatic setting applies supplemental wage withholding to modeled wage compensation. Use Custom federal withholding rate only when payroll or the equity platform shows a different rate.
7. Open Advanced for prior supplemental wages, state or local planning rates, state withholding, transaction fees, NIIT, and display currency. The state fields are flat planning rates, not state-specific filing rules.
8. Review Equity Tax Summary first, then use Award Tax Ledger, ISO AMT Watchlist, Review Notes, Tax Mix, and Sale Price Curve to check the details behind the headline result.

If Review Notes flags an out-of-the-money option, ISO AMT preference, capital loss, high supplemental withholding portion, or ISO holding-period concern, fix that assumption before relying on Tax gap after withholding or Net cash after tax.

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 or local tax, NIIT, and ISO AMT exposure. It is not the same thing as withholding, and it is not a complete tax return.

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

The false-confidence risk is treating a clean summary number as proof that the tax issue is settled. Read ISO AMT Watchlist and Review Notes with the summary, especially when the event involves ISO shares, a sale below basis, high income, prior supplemental wages, or manual state rates.

Technical Details:

Equity compensation tax starts with the event classification. RSU vesting and NSO exercise commonly create compensation income before the later investment sale is measured. ISO exercise has a split regular-tax and AMT pattern: regular tax often waits until the stock is sold, while AMT can include the exercise spread when shares remain held after year-end.

Sale treatment depends on basis and holding period. RSUs and NSOs usually use fair market value at vest or exercise as regular basis. A qualifying ISO sale uses strike price as regular basis and can turn the full sale gain into long-term capital gain. A disqualifying ISO sale can split the result, with ordinary income limited by the exercise spread and the amount by which sale price exceeds strike price.

The formula core below shows the main arithmetic. Positive capital gain can feed capital-gains tax, optional state capital-gain tax, and NIIT. A capital loss is reported as a loss in the output, but capital-loss deductions, wash sales, and carryovers are outside this single-event estimate.

Federal ordinary income tax is incremental. The calculation compares tax on other taxable income plus equity ordinary income and short-term gain with 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 tax and withholding are payment mechanics, not final tax measurements. RSU and NSO compensation can be subject to employee Social Security, Medicare, and Additional Medicare tax. Federal supplemental withholding is a credit against tax, so a 22% withheld RSU vest can still leave a tax gap when the incremental income tax, payroll tax, state tax, and investment-income tax are higher.

The ISO AMT estimate is deliberately narrow. ISO preference starts with the spread on ISO 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. That can flag possible ISO exposure, but it does not rebuild Form 6251 with every AMT adjustment, credit, exemption interaction, or future AMT credit carryforward.

Limitations and Responsible Use:

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 can change. Compare any filing-year estimate with current IRS and SSA guidance before filing or making an estimated tax payment.
• Flat state or 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 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 400 shares are sold at $31 and the remaining 600 shares are held, the output shows Total tax estimate of $8,959.00, Withholding credits of $8,063.00, Tax gap after withholding of +$896.00, and Net cash after tax of -$2,584.00 with the stated 2026 single-filer assumptions and 7% state planning rates. 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 $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. 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 Review Notes reports a capital loss or 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:

Fair market value (FMV)

The per-share value used at vesting or exercise to measure RSU income, option spread, or ISO AMT preference.

Strike price

The per-share amount paid to exercise an option.

Spread

The positive difference between FMV and strike price for an option share.

Supplemental wage withholding

Federal wage withholding applied to compensation such as bonuses, commissions, RSU income, and option wage income.

Alternative minimum tax (AMT)

A parallel federal tax calculation that can include ISO spread even when regular tax has no income at exercise.

Net Investment Income Tax (NIIT)

A 3.8% federal tax that can apply to investment income when modified adjusted gross income exceeds filing-status thresholds.

Disqualifying sale

An ISO sale that does not meet the ISO holding-period requirements and can create ordinary income.

References:

• Topic no. 427, Stock options, Internal Revenue Service.
• Publication 525, Taxable and Nontaxable Income, Internal Revenue Service.
• Publication 15, Employer's Tax Guide, Internal Revenue Service.
• IRS releases tax inflation adjustments for tax year 2026, Internal Revenue Service.
• 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.
• About Form 3921, Exercise of an Incentive Stock Option Under Section 422(b), Internal Revenue Service.