rsus and the tax bill nobody warns you about

what an RSU actually is

A restricted stock unit is an unfunded promise from your employer to deliver shares at a future date, conditional on continued service. Nothing happens at grant — no tax, no ownership, just a promise on a vesting schedule.

When they vest, shares are delivered and the market value that day is compensation, identical in character to salary. It goes on your W-2 like wages.

The framing that prevents most mistakes: RSUs are compensation first and investments second — earned income that happens to be delivered in shares, not a discretionary stock position. If your employer handed you the cash equivalent, would you use all of it to buy company stock? That's the actual decision you're making by holding.

the 22% problem

Here's the mechanism behind nearly every RSU tax surprise.

RSU income is classified as supplemental wages — the same bucket as bonuses — and supplemental wages get flat-rate withholding: 22% until cumulative supplemental wages pass $1 million in a calendar year, then a mandatory 37% on the excess.

That's fine if you're in the 22% bracket. If your salary plus vesting RSUs puts you in the 32% or 35% bracket, the company under-withheld by 10 to 13 percentage points on the RSU portion — and the shares are already gone, sold at vest.

The fix is unglamorous: make a Q4 estimated tax payment, or add extra withholding via your W-4, in any year with meaningful vesting. Some states — California in particular has a front-loaded estimated tax system where paying in full by year-end isn't always enough to avoid penalties — require paying earlier, not just paying enough.

double-trigger RSUs at private companies

If you work somewhere pre-IPO, your RSUs almost certainly have two locks, and only one is the vesting schedule you watch in your equity portal.

Double-trigger RSUs deliver shares only after both a time-based schedule and a liquidity event — IPO, acquisition, or sometimes a tender offer — are satisfied. There's no tax at grant and none when units time-vest while the company is private.

Then the second trigger fires. At settlement, the full market value of every delivered share becomes ordinary W-2 income at once — typically withheld at the flat 22% rate even when your real marginal rate is 32% to 37%.

Years of accumulated vesting can settle in a single day, pushing you into the highest brackets in a year when you may also be locked up and unable to sell. The withholding gap that's uncomfortable in a normal vest year becomes very large here.

the filing mistakes that cost real money

1. The $0 cost basis trap. Broker 1099-Bs often report $0 basis for RSU sales. Reporting it that way double-counts income already taxed on your W-2. Adjust to the vest-day fair market value on Form 8949. This is the single most common — and most expensive — RSU filing error, and it's the source of the "am I taxed twice?" confusion.
2. Assuming 22% covered it. For anyone in the 24% bracket or above, it didn't. Plan the shortfall.
3. Vest-and-hold without thinking. Concentration in employer stock is a separate risk from compensation — holding doubles down on a single-stock bet while your salary already depends on that company.
4. Missing multi-state allocation. If you moved during the vesting period, income may be allocable to your prior state — California is famously attentive to equity earned there.
5. Stacking equity events. A heavy vest year is generally the wrong year to also exercise nonqualified options; two forms of equity comp, each reasonable alone, can create a tax bill nobody budgeted for.

One clarifying note on holding: the holding period for long-term capital gains starts at the vest date, not the grant date, and only post-vest appreciation is a capital gain.

should you sell at vest?

There's no universal answer, but there's a useful default and a useful test.

The test: if you received the cash value instead, would you buy that much of your employer's stock today? Most people say no. Holding is the same decision, just disguised by inertia.

The concentration argument: your salary, your health insurance, your bonus, and your RSUs all already depend on one company. Adding a large stock position to that is stacking risk, not diversifying it.

The counterargument: selling immediately means no upside if the stock runs, and there can be tax reasons to hold past a year for long-term capital gains treatment on appreciation.

A common middle path is selling at vest by default and deliberately choosing to hold a specific, limited amount — rather than holding everything by not deciding.

the bottom line

Equity compensation is genuinely valuable and genuinely confusing, and the confusion is expensive in a specific, predictable way: withholding that's too low and a cost basis that's reported wrong.

You don't need to master the whole system. You need to know your actual marginal rate, that 22% probably isn't it, and to check the cost basis on your 1099-B before filing.

Your next tiny step: if you have RSUs vesting this year, estimate your marginal bracket and compare it to 22%. That difference, times your vesting value, is roughly what you should set aside now.