How Equity Compensation Affects Your Tax Return: RSUs, ISOs, and 83(b)

Equity compensation adds layers of complexity to your tax return that most W-2 employees never encounter. RSUs show up in different boxes on your W-2, ISOs require a separate AMT form, and 83(b) elections change how you report income for years to come. If you get any of it wrong, you could double-pay taxes or miss claiming credits you're owed.

This guide walks through each equity compensation type, the IRS forms involved, and the most common mistakes that cost taxpayers thousands of dollars.

Which IRS Forms Apply to Which Equity Type?

Here's the quick reference:

RSUs on Your Tax Return

RSU taxation is the most straightforward of all equity types — but the reporting still trips up many taxpayers.

At Vesting: W-2 Income

When RSUs vest, the fair market value of the shares on the vesting date is treated as ordinary income. Your employer:

1. Reports the income on your W-2, Box 1 (Wages, tips, other compensation). The RSU income is combined with your salary — you won't see a separate line item for RSUs.
2. Withholds taxes — typically 22% federal (supplemental rate), your state's supplemental rate, and FICA taxes (Social Security up to the $176,100 wage base + 1.45% Medicare + 0.9% Additional Medicare if over $200,000).
3. Reports withholding in W-2 Boxes 2, 4, 5, 17 (federal, Social Security, Medicare, state).

Your W-2 Box 14 may include a line labeled "RSU" or "STOCK" showing the RSU income separately, but this is informational only — the amount is already included in Box 1.

Worked Example: Reading Your W-2 With RSU Income

Here's what a W-2 actually looks like for a single filer with $200,000 salary and $80,000 in RSU vesting:

Key verification: Box 1 should equal your salary plus the total FMV of all RSU shares that vested during the year. If it doesn't, contact your employer's payroll department before filing. An incorrect W-2 is one of the most common causes of amended returns.

The hidden shortfall: In this example, Box 2 shows $55,200 in federal withholding. But the actual federal tax on $280,000 (after $15,750 standard deduction = $264,250 taxable) is approximately $57,900. That's a $2,700 shortfall — and that's before adding any state tax gap. See our RSU tax rate guide for how these shortfalls compound at higher income levels.

At Sale: 1099-B and Schedule D

When you sell vested RSU shares, your broker issues a 1099-B reporting the proceeds. This is where cost basis becomes critical.

Your cost basis is the fair market value of the shares on the vesting date — the same amount that was included as W-2 income. Any gain above that basis is capital gain; any loss is a capital loss.

• Held less than 1 year after vesting: Short-term capital gain, taxed at ordinary income rates
• Held more than 1 year after vesting: Long-term capital gain, taxed at 0%/15%/20%

You report sales on Schedule D and Form 8949.

How to check: Compare the "cost basis" on your 1099-B to the FMV on your vesting date. If they don't match, you need to adjust your cost basis on Form 8949 using column (f) — adjustment code "B" (basis reported to IRS is incorrect).

ISOs on Your Tax Return

ISOs have the most complex tax reporting because they interact with two parallel tax systems: regular tax and AMT.

At Exercise (Hold Shares): Form 3921 + Form 6251

When you exercise ISOs and hold the shares (don't sell immediately), your employer issues Form 3921 — "Exercise of an Incentive Stock Option Under Section 422(b)." This form reports:

• Box 1: Date option was granted
• Box 2: Date option was exercised
• Box 3: Exercise price per share
• Box 4: FMV per share on exercise date
• Box 5: Number of shares transferred

No income appears on your W-2 from a qualifying ISO exercise. However, you must complete Form 6251 (Alternative Minimum Tax) because the bargain element (Box 4 minus Box 3, multiplied by Box 5) is an AMT adjustment.

Form 6251 walkthrough:

1. Line 2i: Enter the ISO bargain element as a positive adjustment
2. Complete the AMT calculation (lines 1-11)
3. Compare tentative AMT to regular tax
4. If AMT exceeds regular tax, the difference goes on Form 1040, Schedule 2, Line 1

If you owe AMT, you've also generated an AMT credit carryforward that you'll claim on Form 8801 in future years. See our AMT calculator guide for a detailed walkthrough.

At Sale: 1099-B + Potentially W-2

When you sell ISO shares, the tax treatment depends on whether you met the holding periods:

Qualifying disposition (held 2+ years from grant AND 1+ year from exercise):

• Entire gain is long-term capital gain (reported on Schedule D)
• No W-2 income
• Any AMT previously paid generates a credit (Form 8801)

Disqualifying disposition (sold before meeting holding periods):

• The bargain element becomes ordinary income (reported on W-2)
• Any additional gain above FMV at exercise is capital gain
• AMT adjustment is reversed (you may get AMT credit back faster)

83(b) Elections on Your Tax Return

An 83(b) election fundamentally changes how restricted stock is reported on your tax return — both in the year of the election and in all subsequent years.

Year of Election: Immediate Income Recognition

When you file an 83(b) election within 30 days of receiving restricted stock or early-exercising options:

1. You report the FMV of the stock at the time of the election as ordinary income on your tax return for that year. If the stock has minimal value (e.g., a $0.01 FMV per share at an early-stage startup), the income may be negligible.
2. Your employer should include this amount on your W-2. If they don't (common at early-stage startups), you may need to report it directly.
3. File Form 15620 (or a letter meeting the requirements of IRC Section 83(b)) with the IRS. Attach a copy to your tax return.

Keep a copy of everything. The IRS may not acknowledge receipt of your 83(b) election for months (or ever). Having proof of timely mailing (certified mail receipt) is essential.

Subsequent Years: No Additional Income at Vesting

This is the key benefit. Without an 83(b) election, you'd recognize ordinary income on each vesting date based on the FMV at that time. With an 83(b) election, vesting dates have no tax consequence — you already paid tax on the full value upfront.

At Sale: Capital Gains

When you eventually sell the shares:

• Held more than 1 year from the 83(b) election date: Long-term capital gains on all appreciation above the amount you reported as income
• Held less than 1 year: Short-term capital gains

The difference between paying 37% ordinary income tax on appreciation versus 20% long-term capital gains tax is why the 83(b) election can save tens or hundreds of thousands of dollars at high-growth startups.

For a complete walkthrough with examples, see our 83(b) Election Guide. To model the tax savings for your specific situation, use our 83(b) Election Calculator.

ESPP on Your Tax Return

Employee Stock Purchase Plans (ESPPs) under Section 423 get a brief mention here because they're common in public tech companies:

• At purchase: No income recognition (for qualifying ESPPs)
• At sale — qualifying disposition (held 2+ years from offering date, 1+ year from purchase): The discount is ordinary income (reported on W-2), remaining gain is capital gain
• At sale — disqualifying disposition: The spread at purchase is ordinary income (W-2), remaining gain/loss is capital gain/loss

Your employer reports ESPP income on your W-2 when a disqualifying disposition occurs. The broker reports the sale on 1099-B.

Common Mistakes That Cost Thousands

1. Double-Counting RSU Cost Basis

As mentioned above, if your broker reports $0 cost basis on the 1099-B and you don't adjust it, you're paying tax on the RSU income twice. This is the single most common equity tax mistake and can cost $5,000-$20,000+ depending on the size of your RSU package.

Fix: Always adjust the cost basis on Form 8949 to match the FMV on the vesting date.

2. Missing the AMT Credit from ISO Exercises

If you paid AMT in a prior year due to ISO exercises, you have an AMT credit carryforward. Many taxpayers (and their tax preparers) forget to file Form 8801 to claim this credit in subsequent years. The credit doesn't expire, but you won't get it unless you claim it.

Fix: If you've ever paid AMT, ensure Form 8801 is included in every subsequent tax return until the full credit is recovered.

3. Reporting 83(b) Election Income in the Wrong Year

The income from an 83(b) election is reported in the year you received the stock (and filed the election), not in the year the stock vests. If your tax preparer reports vesting-date income despite an 83(b) election, you'll pay tax twice.

Fix: Provide your tax preparer with a copy of the 83(b) election and confirm they understand no additional income should be reported at vesting.

4. Missing the 83(b) Filing Deadline

This isn't a tax return mistake per se, but it's devastating: if you miss the 30-day deadline to file your 83(b) election, you cannot retroactively file one. You'll owe ordinary income tax on the full FMV at each vesting date. Track the deadline carefully using our 83(b) Election Calculator.

5. Not Reporting ISO Exercises on Form 6251

Even if your AMT doesn't exceed your regular tax (meaning you owe zero additional AMT), you should still complete Form 6251 to establish your AMT basis in the shares. This matters when you eventually sell — your AMT cost basis is the FMV at exercise, while your regular tax cost basis is the exercise price.

Timeline: When You Receive Each Form

Getting Help

Equity compensation taxes are genuinely complex. Even experienced tax preparers sometimes make mistakes with ISOs and AMT credits. When choosing a tax professional:

• Ask if they have experience with ISO exercises and AMT calculations
• Confirm they know how to file Form 8801 for AMT credit carryforward
• Verify they'll adjust 1099-B cost basis for RSU sales
• If you have an 83(b) election, provide documentation and confirm they understand the reporting

For quick calculations and planning, use our free calculators:

• RSU Calculator — withholding shortfall and tax breakdown
• ISO AMT Calculator — AMT-free exercise limit
• 83(b) Election Calculator — tax savings analysis

For the underlying bracket math, reference our 2026 Federal Tax Brackets. If your ISO exercise or RSU vesting creates a shortfall, see our guide on estimated taxes after ISO exercise.

Frequently Asked Questions

Do I need to report RSU income on my tax return separately from my W-2? No. RSU vesting income is already included in your W-2 Box 1 — it's combined with your salary. You don't report it separately on a different form. However, if you sell RSU shares, you report the sale on Schedule D and Form 8949 using your 1099-B. The critical step is ensuring the cost basis on Form 8949 matches the FMV on the vesting date, not the $0 that many brokers report.

How do I report ISO exercises on my tax return? If you exercised ISOs and held the shares (didn't sell the same year), you file Form 6251 (Alternative Minimum Tax). Enter the bargain element (FMV at exercise minus exercise price, times number of shares) on Line 2i. Even if your AMT doesn't exceed your regular tax, complete Form 6251 anyway — it establishes your AMT basis in the shares, which matters at sale. Your employer provides Form 3921 with all the exercise details you need.

What if my 1099-B shows the wrong cost basis for RSU shares? This is extremely common. Many brokers report $0 or the pre-vesting value as cost basis instead of the FMV at vesting. If you don't fix this, you'll pay tax on the RSU income twice — once through your W-2 and again as capital gain. On Form 8949, use column (f) with adjustment code "B" (basis reported to IRS is incorrect) and enter the correct basis. The correct basis equals the FMV per share on the vesting date multiplied by shares sold.

Do I owe taxes when I exercise ISOs, or only when I sell? Both — but in different tax systems. Exercising ISOs doesn't create regular income tax, but the bargain element is added to your Alternative Minimum Taxable Income (AMTI). If this pushes your AMT above your regular tax, you owe the difference as AMT in the exercise year. When you sell, the tax treatment depends on holding periods: a qualifying disposition (2+ years from grant, 1+ year from exercise) is all long-term capital gains; a disqualifying disposition converts the bargain element to ordinary income on your W-2.

How does an 83(b) election change what I report on my tax return? In the year of the election, you report the FMV of the stock as ordinary income (even if it's $0 at an early-stage startup). In subsequent years, you report nothing at each vesting date — the 83(b) means you already paid tax on the full grant. At sale, all appreciation above the election-date value is capital gain (long-term if held over 1 year from the election). This can save 17+ percentage points on every dollar of growth compared to vesting without an 83(b).