Your RSUs Vested, You Sold Nothing, and Now You Owe $14,000 in April

The number in the corner of the screen

The import finished, the W-2 loaded, and the running total in the corner went red. Balance due. Five figures.

Your first thought is that it's a bug, because you watched the withholding happen. Shares came off the vest. The broker's confirmation said so. You didn't get all of it, you got most of it, and the rest went to the government the way it does on every paycheck.

Some of it did. Not enough.

And the money is gone — into a wedding, a car, eleven months of ordinary life — and the shares you kept are worth less than they were on the vest date, which is a separate insult.

This is the default outcome of a rule most people never hear about until the year it bites them.

One piece of housekeeping before any of the numbers: every rate below is a current-year figure and they move. Check yours before you rely on them.

Why the number was 22%

A vest is treated as supplemental wages — the same bucket as a bonus. When an employer uses the flat-rate method for supplemental wages, the statutory rate is 22% for the first $1,000,000 of supplemental wages in a calendar year, and 37% on anything above that. It's laid out in IRS Publication 15, section 7. An employer can instead use the aggregate method, which folds the payment in with your regular wages; the flat rate is the common one, and it's the one that produces this article.

Read that again with the important part in mind: 22% is not an estimate of your tax rate. It is a fixed default. The same number for someone earning $70,000 and someone earning $400,000.

So if your marginal rate is higher than 22% — and a decent vest on top of a decent base will do that — the shortfall was baked in on the vest date. Nobody at your company told you because nobody at your company is responsible for telling you. Payroll ran the rule correctly.

The advice that doesn't help

Every article on this says RSUs are taxed as ordinary income at vest and then stops, which is true and does nothing for you in March.

Four things you'll be told this week that are wrong, or wrong enough to cost you money:

“Just fix your W-4.” The W-4 doesn't control the flat supplemental rate. It controls withholding on your regular wages. You can add a flat extra amount on line 4(c), which helps, but it spreads a lumpy problem across every paycheck of the year, including the quarters with no vest in them. A blunt instrument for a spiky bill.

“File an extension and buy yourself six months.” An extension extends the time to file. It does not extend the time to pay. Interest and the failure-to-pay penalty run from the original deadline either way. People lose real money to this misunderstanding every year.

“Sell the shares to cover it.” Sometimes right. But if the stock is below where it vested, selling doesn't shrink this bill by a cent. Your cost basis is the vest-day price, so a sale below it produces a capital loss, and a capital loss offsets capital gains first and then only $3,000 of ordinary income a year, with the rest carried forward. The tax you owe is on income you recognized at vest. That figure is fixed. What the share price did afterwards is a separate story with separate rules.

“Harvest the loss while you're at it.” If your vests are quarterly, selling at a loss while more shares are landing within thirty days on either side can put you into wash sale territory, because a vest is an acquisition of the same stock. Get a preparer to look at the dates rather than guessing at them.

Size the hole exactly, before April

You don't have to wait for the software to tell you.

Pull the vest income. It's on the pay statement for the vest date, and it's already inside box 1 of your W-2. Take your actual marginal federal rate, subtract 22%, multiply by the vest income. That's the bulk of the federal gap.

Say 2,000 shares vested at $55. That's $110,000 of ordinary income. Withheld at 22%, that's $24,200. If the top of that income sits in a 35% bracket, the federal tax on it is somewhere near $38,500 — call the gap about $14,300. Your real number will differ, because the $110,000 doesn't all land in one bracket and because everything else on your return moves it. Treat it as a planning figure.

Then there's the state, which many people forget until the second bill arrives. Plenty of states apply a flat supplemental rate to a vest too, often below your actual state rate, so the same gap opens on a smaller scale. There's the Additional Medicare Tax as well — 0.9% on wages above $200,000 for a single filer, $250,000 married filing jointly — and an employer only has to start withholding it once you pass $200,000 with that employer, so if you're married filing jointly, or you changed jobs mid-year, it can go unwithheld and show up on the return. And there's a possible underpayment penalty sitting on top of the tax itself. Broadly, you're clear of that if withholding plus estimated payments reach 90% of this year's tax or 100% of last year's — 110% if your prior-year AGI was over $150,000.

There's a lever hidden in that last one. Withholding is generally treated as paid evenly across the year no matter when it actually happened, while an estimated payment counts when you make it. So catching this in November rather than March changes what's available to you: cranking payroll withholding up for the last two months can repair an underpayment from a February vest in a way that writing a check in November can't.

Paying it

If you still hold the shares, selling is usually the cheapest route, and it's cheapest for a reason that has little to do with tax. You are holding a large, undiversified position in the company that also pays your salary and your health insurance. Almost nobody would build that position deliberately with cash. If the shares are near their vest price, selling costs you little beyond concentration you probably didn't want in the first place. If they're well down, this doesn't fix April, though it may still be the right move for reasons that have nothing to do with April.

Cash is the obvious alternative, and an emergency fund exists for exactly this. The only question is whether paying in full empties it.

If neither covers the bill, the IRS has two plans, and the arithmetic on them is worth doing properly rather than by feel. There's a short-term option of up to 180 days, and a long-term installment agreement with a setup fee that's reduced for direct debit and can be waived on low income. The failure-to-pay penalty runs at 0.5% of the unpaid tax per month, cut to 0.25% if you filed on time and have an approved long-term installment agreement — that reduction attaches to the long-term agreement, so a short-term plan halves nothing, which is the detail people get wrong when they're comparing the two. Interest is set quarterly and compounds daily; look up this quarter's rate rather than accepting anyone's remembered figure, mine included. Run both of those against whatever it would otherwise cost you to raise the money. Paying a federal tax bill with a credit card usually loses that comparison, because the processors charge a percentage fee to accept it and a card APR then runs on top of the fee. A 401(k) loan carries its own trap: leaving or losing the job can accelerate repayment.

For the filing itself — especially with multiple states, a mid-year move, or equity beyond plain RSUs — get a CPA or an enrolled agent. The cost of one is small next to the size of the mistakes available here. And for the week before you can get an appointment, when you can't tell whether you're in trouble or just embarrassed, TrueTalk has an advisor called Financial Planner Frank, an AI persona built around financial planning and investing, which is a place to work the arithmetic through out loud.

Stopping it happening again

Ask payroll, in writing, whether they can withhold on supplemental wages at a rate above 22%. Some providers allow it. Plenty don't, and you want to know which you're dealing with before the next vest date rather than after.

If they can't, the precise tool is an estimated payment in the quarter the vest lands, using Form 1040-ES or the IRS's own online payment system, sized to the gap you just calculated. Line 4(c) on the W-4 is the blunter alternative.

And sell the shares as they vest. That's the default, and it doesn't fit everyone — executive holding requirements override it, and if you trade in blackout windows, ask about setting up a plan in advance rather than deciding each quarter. But the tax is owed whether you sell or not, so holding is an active decision to keep buying your employer's stock with money that was briefly yours.

Whichever way you settle this one, put the next vest date in your calendar now, with a reminder two weeks before. That's the whole fix. The rest of this article exists because that reminder didn't exist last year.