RSU Sell-to-Cover vs Net-Settlement: 4,200 Shares

Priya is a senior product manager in Seattle. On May 15, 4,200 of her restricted stock units vest at a fair market value of $50 per share — $210,000 of ordinary income added to her W-2 in one day. She files single, lives in Washington (no state income tax), and her total taxable income for the year lands her in the 35% federal bracket. Her equity portal asks one question before the shares settle: sell-to-cover or net settlement? She has read that one of them leaves her richer. It is the wrong thing to obsess over.

Both methods cover her tax bill by surrendering the same 22% of the vest. Both leave her with about 3,276 shares and a few dollars of difference. The decision that actually determines whether Priya writes a five-figure check next April is something neither button on the screen mentions: the gap between the 22% her employer withholds and the 35% she truly owes.

The two mechanics, side by side

An RSU vest is taxed as ordinary compensation at the moment it vests, under IRC §83. The full $210,000 hits her W-2 as wages, and the employer must withhold federal tax just like on a bonus. Employers use the supplemental-wage withholding rule: a flat 22% on supplemental wages up to $1M per year, 37% on anything above $1M (IRS Pub. 15, §7; IRC §3402). The only question is how the company hands the IRS that 22%.

• Net settlement (share withholding). The company never issues you the shares it needs for taxes. It calculates the withholding, holds back enough whole shares to cover it, and deposits the rest into your brokerage account. No shares touch the open market. There is no sale, no commission, and no Schedule D entry on the withheld shares.
• Sell-to-cover. The broker issues you all 4,200 shares at the $50 vest-date basis, then immediately sells just enough on the open market to raise the withholding cash and remits it. This is a genuine same-day market sale — it carries a small commission and a tiny gain or loss, and it generates a Form 1099-B you must reconcile.

The math on Priya’s 4,200 shares

Start with the number that drives everything: 22% of $210,000 is $46,200 of required federal withholding. At a $50 share price, that is exactly 924 shares. Because you cannot withhold a fraction of a share, both methods round to whole shares — and here $46,200 ÷ $50 is a clean 924, so there is no rounding gap at all in this example.

Read the bottom two rows. The share counts match. The only operational differences are a small brokerage commission and a few dollars of fractional cash on the sell-to-cover side — rounding error on a $210,000 event. The identical, six-times-larger number sitting in both columns is the $27,300 shortfall. That is the figure that decides Priya’s April.

Why you still owe $27,300 either way

The 22% supplemental rate is a one-size withholding default, not your tax rate. Priya’s marginal rate is 35% because her total 2026 taxable income falls in the single bracket that runs from $250,526 to $626,350 (IRS Rev. Proc. 2025-32). Her vest is taxed at that 35%:

1. Actual federal tax on the $210,000 vest at 35%: $73,500.
2. Federal tax already withheld at 22%: $46,200.
3. Shortfall carried to her Form 1040: $73,500 − $46,200 = $27,300.

That 13-percentage-point gap (35% − 22%) is structural. It exists for every high earner whose marginal rate exceeds 22%, and it is completely independent of the sell-to-cover-versus-net-settlement choice. Pick either button and you are still $27,300 short unless you do something about withholding before year-end. Worse, a large under-payment can trigger an underpayment penalty under IRC §6654 if you don’t hit a safe harbor (generally 90% of this year’s tax or 110% of last year’s for higher earners).

What most people get wrong

The myth is that net settlement “saves on taxes” or “leaves you more shares.” It does not. The withholding amount is fixed by the 22% supplemental rule regardless of method — the company must remit $46,200 either way. What net settlement genuinely avoids is a market sale: no shares trade hands publicly, so there is no Schedule D reporting on the withheld shares and no commission. That is a paperwork-and-pennies advantage, not a tax advantage.

The second myth is the opposite error: assuming the $46,200 already withheld “handles the taxes.” It handles 22% of them. The people who get blindsided in April are the ones who saw a big withholding number on their pay stub, assumed they were square, and never modeled the 35% reality. The withholding method is a distraction; the withholding rate is the event.

The cost-basis trap on shares you keep

Both methods leave Priya with 3,276 shares, and those shares carry a cost basis equal to the vest FMV — $50 per share — because that value was already taxed as W-2 income under IRC §83. If she later sells at $60, she owes capital-gains tax only on the $10/share appreciation, not the full $60.

The recurring disaster: brokers frequently report a $0 cost basis on Form 1099-B for vested RSUs. If Priya files that figure unchallenged, she pays tax a second time on income already on her W-2 — a $163,800 phantom gain on 3,276 shares. Always adjust the basis to the vest FMV on Form 8949 (column (g)). This is true whether the shares came through sell-to-cover or net settlement.

When the method actually matters

For the typical vest, treat the two as interchangeable and let your plan default ride. There are a few edges where it’s worth electing deliberately:

• Trading windows and 10b5-1 plans. If you’re an insider subject to blackout periods, an open-market sell-to-cover can collide with trading restrictions. Net settlement (no market transaction) sidesteps that entirely — which is one reason many plans default to it.
• You want to keep every share. Some plans offer a third option: pay the withholding with outside cash (a check or ACH) so neither method touches your shares. If you’re bullish and have the liquidity, this keeps all 4,200 shares — but it does not fix the $27,300, it adds the $46,200 to your out-of-pocket cost.
• Volatile stock and same-day timing. Sell-to-cover sells at the actual market price on settlement day, which may differ from the $50 vest FMV used for income reporting. A sharp intraday move creates a small short-term gain or loss to report. Net settlement avoids the timing noise.
• Wash-sale awareness. If you sold the same stock at a loss within 30 days, a sell-to-cover sale can interact with wash-sale rules (IRC §1091). Net settlement, having no sale, has no wash-sale footprint.

The default-override matrix

State withholding adds a second layer

Priya catches a break: Washington has no personal income tax, so the only withholding question on her vest is federal. For anyone in a state that taxes wages, the company applies a separate state supplemental rate on top of the 22% federal — and that rate is just as likely to under-withhold against a high marginal bracket. A Californian on the same $210,000 vest would see 10.23% state supplemental withholding on equity comp (FTB DE 44), which trails California’s top marginal rate of 13.3%. The structural lesson is identical: the supplemental flat rate is a floor, not a settlement, and the gap surfaces at filing.

Note that the method choice has no effect on state tax either. Whether the company net-settles or sells to cover, the same dollar amount of state and federal withholding is remitted, and the same retained-share count results. Your residency and bracket set the bill; the settlement mechanic just decides whether a few shares briefly route through the open market.

The lever that actually moves money

Priya should stop debating the two buttons and close the $27,300 gap. Three ways to do it, in order of cleanliness:

1. Elect a higher supplemental rate at vest, if your plan allows it. Some equity plans let you withhold above 22% on the vest itself — the cleanest fix because the money is taken at the source, in shares, exactly when the income is recognized.
2. Increase W-2 withholding on Form W-4. Add an extra per-paycheck amount on line 4(c) for the rest of the year. Because withholding is treated as paid evenly across the year, this can also cure an earlier-quarter underpayment.
3. Make a quarterly estimated payment (Form 1040-ES). Send the 13% shortfall — about $27,300 here — for the quarter the vest landed in, so you satisfy the §6654 safe harbor and avoid the underpayment penalty.

The decision lever is not sell-to-cover versus net settlement. It is whether you withhold at 22% and discover the rest in April, or withhold at your real 35% and walk into filing season already square. Pick the default that fits your trading status, then go fix the rate.