You were promised 100 shares. On vest day, 62 appeared. No email explained the other 38, and your brokerage history shows a sale you never ordered. Welcome to sell-to-cover — the default tax plumbing behind most RSU plans, harmless when understood, and the source of two genuinely expensive misunderstandings when it isn’t.
The mechanic in one paragraph
Vesting RSUs create ordinary income, and employers must withhold tax on it just like on salary. But a vest delivers shares, not cash — so the plan converts some shares into cash by selling them the moment they vest. Proceeds go to payroll, payroll remits them to the IRS and your state as withholding, and the remaining shares land in your account. The whole sequence is automated and typically settles within a couple of trading days of the vest date.
Why 35-40% of shares can vanish
The withheld fraction mirrors the stacked withholding rates, not just federal income tax:
| Layer | Typical rate at vest |
|---|---|
| Federal income tax (supplemental flat rate) | 22% (37% above $1M supplemental for the year) |
| Social Security | 6.2% until year-to-date wages hit the wage base ($176,100 in 2025), then 0% |
| Medicare (+ Additional Medicare over $200k/$250k) | 1.45% (+0.9%) |
| State income tax | 0-10.23%+ depending on state (CA equity supplemental: 10.23%) |
Early in the year, before the Social Security cap is reached, total withholding easily lands in the mid-30s percent — hence 100 shares becoming 62. Later-year vests, after the cap, keep slightly more. Plans round share counts (you cannot sell 37.4 shares), so tiny cash residues or an extra share sold are normal.
The first misunderstanding: “I was taxed on shares I never got”
You did get them — for about a heartbeat. The clean way to think about it: the company paid you a bonus equal to 100 shares’ value, you owed withholding on that whole bonus, and 38 shares’ worth was spent paying it. The 100-share value sits in your W-2 exactly once. Nothing about the sale adds tax; it merely pays tax you already owed.
The second misunderstanding: the surprise 1099-B line
That automatic sale is a genuine market transaction, so your broker reports it on Form 1099-B — frequently with the infamous $0 cost basis. People either omit it (“I never sold anything!” — cue a CP2000 mismatch letter) or report it raw and accidentally pay capital-gains tax on the entire proceeds. The correct treatment is almost boring:
- Report the sale on Form 8949 like any other.
- Basis = vest-date price × shares sold (from the broker’s supplemental statement).
- Result: a gain or loss of a few dollars — whatever the price moved between vest and execution.
Full mechanics, including fixing prior years, live in the $0 cost-basis guide.
Anatomy of one vest
Jordan vests 200 shares at $45 on May 15: $9,000 of W-2 income. The plan sells 70 shares to cover ≈ 31% combined withholding. The sale executes May 16 at $44.80, raising $3,136 sent to payroll. The 1099-B will show: proceeds $3,136, basis $0 (uncorrected). True basis: 70 × $45 = $3,150. Correct reporting yields a $14 short-term loss — not a $3,136 gain. Jordan keeps 130 shares with a $45 basis each.
Sell-to-cover vs. its siblings
| Method | What happens | Notes |
|---|---|---|
| Sell-to-cover | Broker sells just enough shares on the market for withholding | Most common; creates a 1099-B line; tiny gain/loss |
| Net settlement / share withholding | Company keeps back shares and funds withholding from corporate cash; no market sale | No 1099-B for the withheld portion; company bears cash cost |
| Cash withholding | You hand payroll cash; keep all shares | Rare for rank-and-file; requires liquidity and intent to hold |
| Same-day sale of everything | All vested shares sold; taxes withheld from proceeds; rest paid as cash | An election some plans offer; ends concentration by default |
You usually don’t choose the method — the plan does — but it is worth one email to your equity team to learn which applies and whether elections (higher withholding rate, sell-all) exist. Knowing the method tells you exactly what your 1099-B will contain in January.
What still needs your attention
Sell-to-cover handles the deposit, not the bill. The 22% federal layer is frequently below a tech-income marginal rate, so the withholding gap survives intact — measure it and fund it. Separately, the shares that remain after covering are a fresh, fully-taxed investment in a single stock; whether to keep them is a portfolio decision, not a tax one, examined in our concentration guide. Sell-to-cover is plumbing. The decisions on either side of the pipe are still yours.
Key takeaways
- Sell-to-cover means your broker automatically sells a slice of each vest — commonly 22-40% depending on rates — and sends the proceeds to payroll as tax withholding.
- You still received and were taxed on ALL the vested shares; the sold slice was yours for a moment and was spent on taxes.
- Those automatic sales appear on your 1099-B like any other sale — usually with the $0-basis problem — and must be reported.
- Sell-to-cover withholding at 22% federal rarely equals your true tax; the withholding-gap math still applies.
- Alternatives exist (net settlement, cash withholding, same-day sale of everything); which you get is set by your company's plan.
Frequently asked questions
I never clicked sell — why is there a sale on my 1099-B?
Because sell-to-cover is a real market sale executed on your behalf at vest. It is reportable like any other sale, typically with a tiny gain or loss versus the vest price, and it needs the same cost-basis correction as your voluntary sales.
Why was I 'taxed on the tax shares'?
You weren't, despite how the forms look. All vested shares were ordinary income once. The withholding sale then disposed of some shares at roughly their basis, creating a near-zero gain. The double-tax illusion appears only when the sale is reported with a $0 basis.
Can I choose how many shares are sold?
Sometimes. Some plans let you elect a higher withholding rate, supply cash instead, or sell everything at vest. Many plans offer no choice at all. Your stock-plan portal or HR equity team has the definitive answer.
Is sell-to-cover bad?
It's neutral plumbing. The two genuine issues are downstream: the withholding rate is often too low for high earners, and the automatic sales are easy to mis-report. Handle those two and sell-to-cover is just how the machine works.
Educational disclaimer: This guide is general information, not financial, investment, tax or legal advice. Figures refer to the tax years stated and change over time; rules differ by jurisdiction and personal circumstances. Verify current figures with the IRS / HMRC and consult a qualified professional before acting. See our full disclaimer.