The RSU Withholding Gap: Why Tech Employees Owe Surprise Taxes Every April

Your employer is almost certainly not withholding enough on your RSUs. The IRS allows a flat 22% supplemental rate on equity compensation, so if your total compensation puts you in the 32%, 35%, or 37% bracket, the shortfall is real and it is yours to solve, not your company's.

The Math That Creates the Bill

The 22% supplemental rate is a matter of federal tax convenience, not an estimate of what you owe. It works for employees earning under roughly $100,000. For a software engineer pulling $250,000 in base salary with a sizable annual vest, it is significantly short.

Here is a scenario I walk through with clients. Imagine $300,000 worth of shares vest in a single calendar year. Your employer withholds 22%, or $66,000 in federal tax. At a 35% marginal rate, the actual federal liability is closer to $105,000. That is a $39,000 gap before state taxes. In a high-tax state like California, the number climbs further.

The shock in April is not a surprise. It is the predictable output of a rule most employees never read.

Sell-to-Cover Does Not Cover Enough

Most equity plans default to sell-to-cover: the company sells just enough shares at vest to fund the 22% withholding, and the rest transfer to you. It feels like you kept more shares, and you did. Those shares arrived carrying a tax liability your paycheck never collected.

Two mechanics are worth understanding. Some plans let you elect a higher withholding rate at vest, often up to the top bracket. Not every employer offers this, and it is the first question worth asking yours.

Second, if withholding is chronically short, the IRS expects quarterly estimated payments. Missing them adds underpayment penalties on top of the tax itself. The 2026 safe-harbor thresholds are 100% of prior-year tax liability, or 110% if your adjusted gross income exceeded $150,000 in the prior year.

Then there is the share decision. Selling at vest locks in ordinary income treatment. Holding creates capital gain exposure and concentration risk. The right answer depends on your bracket, your position size, and what already sits in your portfolio. That sequencing is Soil-layer work in the Sporos Doctrine.

The Takeaway

The fact that changes your answer is your full-year income, not the size of the vest. Two engineers with identical grants can owe very different amounts once a spouse's income, a bonus, or a December vest enters the picture.

The people who get hurt here usually did the responsible thing. They checked the vest confirmation, saw that taxes had been withheld, and reasonably concluded the matter was handled. Nothing on that statement tells you the rate applied was 22% when your bracket is 35%. By the time a preparer catches it, the year has closed and the fixable window is behind you.

If you vest RSUs and your total compensation is above $200,000, assume there is a gap and size it now rather than in March. The last quarter of the year is when the math is still fixable, and running your specific vest schedule while it is open is worth a conversation.

The information provided is for educational purposes only and does not constitute investment, legal, or tax advice. Consult with qualified professionals for guidance specific to your situation.