RSU Taxes: The Double-Taxation Trap and the 22% Withholding Lie

Restricted stock units hit your W-2 as ordinary income on vesting day. That part most engineers understand. What they don't understand is what happens next: your broker reports the vested shares as having zero cost basis on your 1099-B. You end up paying income tax on the vesting event, then capital gains tax on the same dollars again. The 22% federal supplemental withholding that hit your paycheck? It's nowhere close to your actual tax bracket. You're a 32% earner getting hit with 22% withholding, then owing another 9% plus state taxes plus NIIT. RSUs don't just defer taxes—they weaponize them.

How RSU Taxation Actually Works

When an RSU vests, the IRS treats it as compensation income. You receive ordinary income equal to the fair market value of the shares on vesting day. That income flows to your W-2, gets hit with federal and state withholding, and stacks on top of your salary. Unlike stock options, there's no preferential long-term capital gains rate here—it's straight W-2 wages.

Your cost basis in those shares is the FMV on vesting day. That's crucial. If a share vests at $84, your basis is $84 per share. Any gain or loss from that point forward is a capital gain or loss. But your broker doesn't know this. When you sell, it reports the trade on a 1099-B with a cost basis of zero. The IRS computer then sees you selling shares you bought for nothing, triggering capital gain on the entire sale proceeds.

The Worked Example: 1,200 RSUs at $84

You're a senior engineer at a public company. In February 2025, 1,200 RSUs vest. The stock price is $84 per share. Your W-2 gross income for that day: $100,800 (1,200 × $84). You're in a 32% federal bracket, 9.3% California state bracket, and subject to the 3.8% Net Investment Income Tax.

Payroll withholding hits you with 22% supplemental federal withholding: $22,176. State withholding takes another ~7%: $7,056. You net $71,568 into your brokerage account. Your cost basis: $84 per share on 1,200 shares. Your broker records basis: $0 per share.

The withholding gap is immediate. You owed 32% federal on this income, but only 22% was withheld. That's a $12,096 underpayment right there ($100,800 × 10%). Add state taxes and NIIT: you're looking at a total tax bill of roughly $48,300 (32% + 9.3% + 3.8%), but only $29,232 was withheld. You owe $19,068 when you file, before any other income adjustments.

The Sell-to-Cover Trap

Many engineers use a sell-to-cover strategy: immediately sell enough shares to cover taxes, hold the rest. In this scenario, you sell 600 shares at $84 to cover withholding and some taxes. The broker generates a 1099-B showing you sold 600 shares at zero basis for $50,400 proceeds. The IRS sees a $50,400 short-term capital gain. You've now paid income tax on the full $100,800 vesting event, then capital gains tax on $50,400 of that same money. That's double taxation in its purest form.

The correct treatment is that those 600 shares had a $50,400 basis ($84 × 600). Your actual short-term gain is zero. But you'll file Schedule D reporting basis as zero, creating a $50,400 phantom gain unless you manually correct it with an IRS Form 8949.

Why Your Broker's Basis is Always Zero

Brokers receive data from payroll systems, but payroll systems don't transmit the ordinary income amount to the brokerage. The broker sees shares land in your account on vesting day, but no tax information. So it defaults to zero basis. When you file, the broker sends a 1099-B to the IRS with zero basis. You receive a copy. Most people look at the proceeds, assume that's their gain, and report it.

The IRS matches the 1099-B against your tax return. If you report a gain that matches the 1099-B proceeds, the computer accepts it. If you report something different, you get a notice. This is where Schedule D corrections come in—you're telling the IRS you have actual basis information the broker didn't capture.

The Hold Scenario: 8 Months Later

Instead of selling immediately, you hold the remaining 600 shares. In October 2025, the stock hits $97. You sell. The 1099-B shows 600 shares sold at zero basis for $58,200 proceeds, implying a $58,200 gain. But your actual gain is only $7,800 ($97 − $84 = $13 per share × 600). This is short-term capital gain because you've held less than one year from vesting day.

On Schedule D, you correct the basis to $50,400 and report actual gain of $7,800. You'll file Form 8949 to show the basis adjustment. But even if you don't, you've legally sold shares you acquired at $84. The IRS position is that you have documentation (your vesting confirmation) that proves your basis, and the 1099-B is incomplete.

• Vesting event: $100,800 ordinary income; withholding $22,176 federal + ~$7,056 state; actual tax due ~$48,300; shortfall $19,068
• Sell-to-cover 600 shares at $84: broker basis $0, you report $50,400 basis, phantom gain eliminated via Schedule D adjustment
• October sale of 600 shares at $97: broker reports $58,200 gain, actual gain $7,800 after basis correction; short-term capital gain added to income

How the Double-Taxation Trap Compounds

The trap isn't just the 1099-B basis problem. It's that RSU vesting can push you into higher brackets, triggering higher effective rates on all your income. If you vest $100,800 in RSUs and earn $200,000 in salary, your combined income is $300,800. That pushes you from the 24% bracket into the 32% bracket. Your RSU income is taxed at the marginal rate, not a blended rate. You pay 32% on every dollar of the $100,800 vesting event, even though your salary alone would have been 24%.

Then, when you sell those shares months or years later at a gain, you're adding another layer of capital gains tax on dollars that were already taxed as wages. Yes, capital gains are taxed at preferential rates (0%, 15%, or 20%), but 15% on top of the 32% you already paid is still a hit. Add state taxes and the 3.8% NIIT, and your all-in rate on that appreciation easily hits 40%+.

Fixing the Basis Problem Before Filing

The solution is capturing your basis before you sell. When your RSUs vest, screenshot the vesting confirmation showing the share price and number of shares. Keep your tax documents showing the ordinary income amount on your pay stub or Form W-2. When you sell, run a detailed wash check through your broker to confirm your actual cost basis. Most brokers have a cost basis statement tool—use it.

If your broker reported basis as zero and you sold at a gain, file Form 8949 with your tax return showing the correct basis. Attach a note explaining that the 1099-B didn't capture the basis from your vesting event. The IRS computer may flag it for review, but the IRS's own guidance acknowledges that 1099-Bs are often incomplete for RSU sales. You have documentation. You're not hiding anything.

• Document vesting date, share price, and quantity immediately—this is your basis evidence
• Request a detailed cost basis report from your broker before selling; don't rely on the 1099-B
• If basis was reported as zero, file Form 8949 with your return showing the correct ordinary income value as your cost basis
• Consider selling in tranches; sell-to-cover can actually simplify basis tracking if you cover the full tax liability in one transaction

Why the 22% Withholding Matters (And Doesn't)

The 22% supplemental federal withholding rate is not a tax rate—it's a withholding floor. Payroll applies it to windfalls like bonuses and equity vests because it's a safe harbor that covers many people. For a high earner in the 32% bracket, it's a shortfall. For someone in the 12% bracket, it's an overpayment and a free IRS loan until filing.

The real risk is assuming that 22% + state withholding = your total tax bill. It doesn't. You're still liable for the difference between actual tax owed and what was withheld. If you vest $100,800 in RSUs and spend the after-tax proceeds, you might not have cash when your April 15 bill arrives. That's why many engineers use a sell-to-cover strategy—not just to eliminate basis confusion, but to ensure they're liquid for their tax bill.

The 22% withholding does protect you from a huge surprise if you're a low earner, and it's better than no withholding. But it's not a substitute for calculating your actual marginal rate and setting aside cash accordingly. For anyone earning over $100,000, the 22% rate will feel inadequate by April.

Planning Around RSU Taxation

The cleanest approach is aggressive hold-and-diversify. Vest, pay your actual tax bill in cash from other sources (salary, savings, spouse's income), and hold the shares. By holding longer than a year from vesting, you unlock long-term capital gains rates on any appreciation above your $84 basis. If the stock goes from $84 to $110, you pay long-term rates on the $26 gain instead of short-term rates. Over five years and multiple vesting events, this can save tens of thousands.

Alternatively, use a deliberate sell-to-cover approach: sell enough shares on vesting day to cover your full actual tax liability (not just withholding), then hold the rest. This forces you to reckon with your real tax bill immediately and gives you a clear basis story for the sold shares (they were sold on vesting day at the vesting price, zero holding period, no capital gain).

The worst approach is drift: vest, do nothing, and sell in tranches whenever you want cash. This scatters your basis documentation, makes wash sale tracking a nightmare, and guarantees a painful tax bill when you file.