How Much You're Losing on Your Equity Comp Taxes

How much you're losing on your equity comp usually comes down to four quiet leaks: under-withholding at the 22% supplemental rate, the broker cost-basis trap that double-taxes vested shares, bunching income into one high-bracket year, and unplanned AMT on ISO exercises. Each can cost thousands a year.

Equity compensation is one of the best wealth-builders in tech — and one of the easiest to quietly overpay tax on. The losses rarely look like mistakes; they look like a smaller refund, a slightly bigger bill, a number you don't question. This guide names the four leaks, puts a dollar figure on each, and shows how to plug them.

How Much You're Losing: The Four Quiet Leaks

Most equity-comp overpayment traces to four specific leaks, and the reason they go unnoticed is that none of them produces an obvious error message:

1. Under-withholding at the flat 22% supplemental rate.
2. The broker cost-basis trap that taxes already-taxed income a second time.
3. Bunching income into a single high-bracket year.
4. Unplanned AMT from exercising and holding ISOs.

The first two hit nearly everyone with RSUs; the second two hit anyone with options or a large one-year event. None of them is exotic — they're just invisible unless you go looking. The reason they hide so well is that each one produces a result that looks normal: a tax bill instead of a refund, a 1099-B that imports cleanly, a sale that "felt" like the right time, an April number you assume is just what equity costs. Nothing throws an error, so nothing prompts a second look. The first step to stopping the bleed is simply naming the four leaks and putting a dollar figure on each, which is what the rest of this guide does.

Leak 1 — The 22% Withholding Gap

The first and most common leak is that your employer withholds federal tax on RSUs at a flat 22% supplemental rate, even though most tech employees owe 32–37%. The IRS sets that flat rate directly:

"The withholding rate on supplemental wages is 22% ... If the supplemental wages paid to the employee during the calendar year exceed $1 million, the excess is subject to withholding at 37%."

— IRS Publication 15 (Circular E), Supplemental Wages

Because 22% is a statutory flat rate and not personalized to your bracket, it leaves a 10–15 percentage-point shortfall on every dollar of vested RSU income.

The chart below shows how far the flat 22% line sits below the effective rate a higher earner actually owes.

In dollars: a $150,000 vest withheld at 22% sends about $33,000 to the IRS, but at a 35% marginal rate the real federal tax is roughly $52,500 — a $19,500 gap you settle in April. It isn't extra tax; it's tax that should have been withheld and wasn't, which is why it feels like a surprise. The fix is to see it coming: our guides to the RSU withholding gap, how to read your RSU W-2, and why RSUs turn a refund into a bill all show how to close it with estimated payments or a W-4 change before the deadline.

Leak 2 — The Broker Cost-Basis Trap

The second leak is pure waste: paying tax twice on the same income. When you sell vested RSU or ESPP shares, your broker's Form 1099-B often reports a cost basis that is too low — sometimes $0 — because it omits the value already taxed as wages on your W-2. File it unchanged and you pay capital-gains tax on income you already paid ordinary tax on.

Per the IRS Instructions for Form 8949, the fix is to correct the basis with code B. The cost of not fixing it is steep: on $40,000 of RSU shares sold with a $0 basis, you'd report a $40,000 phantom gain and overpay roughly $6,000–$9,500 in capital-gains tax on money that was never really a gain. Our guide to how to file equity comp taxes walks the exact column-by-column fix.

What makes this leak so persistent is that nothing flags it. The 1099-B looks official, tax software imports it cleanly, and the resulting return is internally consistent — it's just wrong in your favor's opposite direction. The only way to catch it is to compare the basis on the 1099-B against the vest-date value that's already in your W-2 wages, lot by lot. People who use a preparer aren't automatically safe, either: unless the preparer specifically reconciles equity-comp basis, they'll often enter the broker figure as-is. Treat every equity-comp 1099-B as guilty until proven innocent.

Leak 3 — Bunching Income Into One Year

The third leak is timing. Because federal tax is progressive, cramming a large exercise or sale into one year stacks more of your income into the top brackets, so you pay a higher rate on the same dollars than if you'd spread them out.

The scenarios above show the same gain sold all at once versus staged across years. A large one-year sale can push otherwise-15% long-term gains into the 20% bracket plus the 3.8% net investment income tax — roughly an 8-point premium on the excess, which on a $400,000 gain is tens of thousands of dollars. The fix is deliberate scheduling, covered in how to optimize equity taxes across multiple years.

This leak is unique in that it costs you nothing to avoid — only patience. The dollars are identical whether you sell in one year or three; the only thing that changes is the rate, which the calendar resets every January. The trap is psychological: a tender offer, an IPO, or a big vesting cliff feels like a single moment to act on, so people sell or exercise the whole position at once and unknowingly route a chunk of it through their highest bracket. Treating the windfall as a multi-year flow instead — and asking "how much can I realize this year before the next bracket?" — is often worth more than any deduction you'll find.

Leak 4 — Unplanned AMT

The fourth leak catches option holders: exercising and holding ISOs creates alternative minimum tax on the bargain element, with no withholding to cover it (IRS About Form 6251). Because nothing is withheld, the bill arrives in April as a pure surprise — on shares you may not even be able to sell.

Exercise 10,000 ISOs at a $2 strike when the FMV is $12, and you create $100,000 of AMT preference income that can drive a five-figure AMT bill. The painful part is that it was usually avoidable: exercising up to your AMT break-even, or staging across years, often keeps it near zero. Our guide to how to avoid triggering AMT lays out the levers.

This leak compounds with the others. Someone who exercises a big ISO block, holds the shares, and also has a large RSU vest in the same year stacks ordinary income and an AMT preference on top of each other — the bunching leak and the AMT leak reinforcing one another into a far larger bill than either alone. And because AMT carries no withholding, there's nothing on a pay stub to warn you it's coming; the first signal most people get is their tax software's number turning red in March. A modest amount of planning before the exercise — checking the break-even, deciding whether to stage — is the difference between a manageable bill and a scramble.

How Much You're Losing Is Fixable: Plug the Leaks

The good news is that all four leaks respond to the same discipline: model before you act. RSUs are ordinary income at vest (IRS Publication 525), options create AMT or ordinary income depending on type and timing, and sales create gains that stack with everything else — so a single annual model surfaces every leak at once.

Think of it as one habit rather than four separate chores. Once a year — ideally early, before any big vest or planned exercise — run your expected income, vests, exercises, and sales through a model and ask the four questions: Is my withholding going to fall short? Will any sale's basis be reported too low? Am I bunching income into this year? Will an ISO exercise trigger AMT? The answers tell you exactly which lever to pull and when. The cost of the habit is an hour or two; the cost of skipping it, as the numbers above show, runs into five figures for many equity holders. It's the highest-return hour in your financial year.

A short checklist:

• Estimate the withholding gap each vest and cover it with estimated payments or a W-4 bump. Map it to your effective rate.
• Adjust your cost basis on every share sale so you're never double-taxed.
• Schedule large exercises and sales across years to avoid bunching.
• Check your AMT break-even before exercising and holding ISOs.

Frequently Asked Questions

How much am I losing on RSU taxes? Often $5,000–$30,000 a year from the 22% withholding gap alone, depending on your bracket and vest size — plus more if a $0-basis 1099-B double-taxes a sale. The exact figure scales with how far your marginal rate sits above 22% and how large your vests are, so a higher earner with big vests loses the most.

Why am I double-taxed on RSUs? A 1099-B that reports a $0 or too-low cost basis taxes income already on your W-2 a second time. Correcting the basis on Form 8949 with code B — using the vest-date value — fixes it.

Does bunching equity income raise my taxes? Yes. Cramming a large exercise or sale into one year stacks income into higher ordinary and capital-gains brackets; spreading it across years keeps more of it taxed in the lower bands instead.

What is an AMT surprise? Exercising and holding ISOs creates alternative minimum tax on the bargain element with no withholding, so the bill lands in April unexpectedly — often on shares you can't yet sell. Because nothing is withheld during the year, there's no pay-stub warning, which is why it catches so many first-time exercisers off guard.

Stop the Leaks Before They Cost You

None of these four losses is inevitable. The difference between an equity package that builds wealth efficiently and one that quietly bleeds tax is almost always a bit of planning a few months ahead. This is general educational information, not individual tax advice — so model your own numbers carefully, and bring a qualified preparer in for a complex year.

For the full picture across every equity type you hold, the equity compensation calculator layers salary, vests, and sales into one annual estimate.