RSU Taxes: The Bill Arrives at Vest, Not at Sale

The day your RSUs vest, the IRS treats them as salary that happened to be paid in shares. One hundred shares vesting at $40 is $4,000 of wages on your W-2, taxed exactly like a $4,000 cash bonus, whether you sell that afternoon or hold for a decade. Almost every RSU mistake traces back to forgetting that single fact.

Vesting is the taxable event

An RSU is a promise of shares that becomes real on a vesting schedule. Until a vest date arrives, nothing is taxed because you own nothing. On the vest date, the market value of the shares that vest is ordinary income: shares times that day's price, added to your wages, taxed at your marginal rate plus payroll taxes. You control none of this. You cannot defer it, the price on that day is the price that counts, and selling versus holding changes nothing about the vest-day tax.

What holding does change is everything after. Once vested, the shares are ordinary stock you own, with a cost basis equal to the vest-day value. Sell later above that value and the difference is a capital gain (long-term if you hold the shares more than a year past the vest); sell below it and you have a capital loss. The capital gains tax calculator prices that second layer. But the $4,000 from the vest itself was taxed as wages no matter what happens next.

The withholding gap

Here is the trap that produces surprise April bills. Employers usually withhold on RSU income the way they withhold on cash bonuses: at a flat supplemental-wage rate, typically by selling or holding back a slice of the vesting shares. That flat rate sits well below the top marginal brackets. For someone whose salary plus vests reaches the upper brackets, every vest is under-withheld by design: the plan sends the IRS less than the income will actually cost, and nobody tells you. A large vest can leave a five-figure gap between what was withheld and what is owed, plus underpayment penalties if the gap is big enough.

The fix is arithmetic, not heroics: estimate the true tax on each vest at your real marginal rate, compare it with what was withheld (the bonus tax calculator shows how flat supplemental withholding treats a lump sum), and cover the difference through extra payroll withholding or an estimated payment instead of discovering it at filing time.

Sell-at-vest is the neutral baseline

Because basis equals vest-day value, selling immediately produces almost no additional tax: the sale price and the basis are the same number, give or take a few days of movement. That makes sell-at-vest the neutral default, and it reframes the real question. Holding vested shares is financially identical to receiving a cash bonus and spending all of it on your employer's stock. Many people would never do the second thing, yet do the first by inaction. The clean test: if the bonus had arrived in cash, would you buy this stock with it today? Holding is a legitimate answer, but it is an active investment decision, not a tax strategy. Waiting for long-term rates only helps on growth after the vest; it does nothing for the wage income already booked.

Concentration risk compounds quietly

RSUs bundle your risks. Your paycheck, your unvested grants, your held shares, and often an employee stock purchase plan all ride the same company. A rough year for the employer can cut the stock and the job at the same time, which is exactly when selling shares to pay bills hurts most. There is no universal threshold, but when a single employer's stock becomes a large slice of your net worth, the hold-versus-sell question stops being about taxes entirely and becomes a diversification question.

The double-count mistake

The most expensive RSU error happens at filing time, years after everything else went right. Worked through: 100 shares vest at $40, so $4,000 lands on your W-2 and your basis is $4,000. Two years later you sell at $46 for $4,600. The true capital gain is $600. But brokers are not always required to report the full basis of compensation shares, so the tax form from the brokerage may show a basis of $0 or just the residual. File it unadjusted and you report a $4,600 gain: you have now paid tax on the same $4,000 twice, once as wages and once as gain. The correction is an adjustment on your return that restores the vest-day basis. Anyone who has ever sold RSU shares should check old filings for this; anyone selling this year should check the basis box on the form before trusting it.

Treat vests like the paychecks they are

A vesting schedule is an income stream with a volatile paymaster: plan the tax at your real rate, decide deliberately what a bonus in stock should become, and keep the share count from quietly dominating everything else you own. That last part is easier when your equity sits next to your accounts in one full picture: concentration you can see is concentration you can manage.