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

Your employer is not withholding enough on your RSUs. Not because of a payroll error, but because the IRS allows employers to use a flat 22% supplemental rate on equity compensation, and the tax code has not updated that default to match where high earners actually land. If your total compensation puts you in the 32%, 35%, or 37% bracket, that gap is your problem to solve, not your company's.

The Math That Creates the Bill

The supplemental withholding rate of 22% applies to RSU vests as a matter of federal tax convenience. It is fine 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 real scenario I walk through with clients: imagine $300,000 worth of shares vest in a single calendar year. Your employer withholds 22%, which is $66,000 in federal tax. But at a 35% marginal rate, the actual federal liability on that income is closer to $105,000. That is a $39,000 gap, before state taxes are added in. In a high-tax state like California, that number climbs further.

The shock in April is not a surprise. It is a predictable outcome 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. The rest of the shares transfer to you. This feels like you are getting more shares, and you are. But those shares came with a tax liability your paycheck never collected.

Two mechanics worth understanding here:

1. Supplemental withholding elections. Some plans allow you to elect a higher withholding rate at vest, often up to the top bracket. Not every employer offers this, but it is the first question worth asking.
2. Quarterly estimated payments. If your withholding is chronically short, the IRS expects you to make up the difference in quarterly installments. Missing them adds underpayment penalties on top of the tax bill itself. The 2026 safe-harbor thresholds are 100% of prior-year tax liability (110% if your adjusted gross income exceeded $150,000 in the prior year).

The mechanical decision of how many shares to sell at vest, and when, also connects to your broader tax picture. Selling immediately locks in ordinary income treatment. Holding creates capital gain exposure and concentration risk. Neither answer is universally right, and the right choice depends on your bracket, your position size, and what is already sitting in your portfolio. That sequencing lives in the Soil layer of a well-built plan, and it is one of the more consequential decisions a high earner makes year after year. (For more on how tax architecture fits into a full retirement framework, see the Sporos Doctrine.)

What to Do Before Year-End

Run through these four questions before December 31:

1. What is my projected total income this year, including all vest dates?
2. What federal and state bracket does that income land in?
3. Have I made or do I need to make quarterly estimated payments to avoid penalties?
4. Is there any tax-loss harvesting opportunity in my taxable account to offset RSU income?

The last quarter of the year is when the math becomes fixable. After December 31, most of the options close.

The Takeaway

If you vest RSUs and your total compensation is above $200,000, assume you have a withholding gap and verify the size of it now, not in March. The surprise tax bill tech employees complain about every spring is almost always this problem, and it is almost always preventable with a mid-year projection and a few deliberate moves before the year closes.

If you want to run the numbers on your specific vest schedule, I am glad to have that 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.