6 Tax Moves Tech Employees With RSUs Should Make Before December

6 Tax Moves Tech Employees With RSUs Should Make Before December

Here's the thing nobody tells you when the offer letter shows up with a big RSU grant: your employer is almost certainly under-withholding your taxes, and you won't find out until April. The RSU year-end tax moves below are how you fix that before the calendar closes the door.

The reason is mechanical. RSUs are treated as supplemental wages, and federal supplemental withholding defaults to a flat 22% (it jumps to 37% only on the portion of supplemental wages above $1 million in a year, per IRS Publication 15). But if your total income lands you in the 35% or 37% bracket — which a senior engineer at a public tech company often does — that 22% withheld is roughly 13 to 15 cents on the dollar short. On a $200,000 vest, that's a five-figure surprise.

These are the RSU year-end tax moves that turn that April surprise into a December decision you actually control. Make them before the calendar flips and the options are still open.

Move 1: The RSU year-end tax move that starts everything — run the real tax on your vest

RSU income is ordinary wages at vest under IRC §83 — taxed the moment the shares deliver, whether you sell or not. The dollar value that hits your W-2 is the fair market value on the vesting date.

So do the math your paystub won't. Add your salary, your vested RSU value, any bonus, and your spouse's income. Find your top marginal rate. If it's 32%, 35%, or 37%, the flat 22% withheld on the RSU portion is not enough — full stop.

The gap: $150,000 vests, withholding takes 22% ($33,000), but you're in the 37% bracket. Your real federal tax on that slice is about $55,500. You're roughly $22,500 short before you've touched state tax.

Knowing the number is the entire game. Everything below is how you close it.

Move 2: Cover the RSU withholding shortfall before year-end, or the IRS adds a penalty

A big vest doesn't just create a tax bill. It can create an underpayment penalty — the IRS charges interest when you haven't paid in enough during the year through withholding or estimated payments.

You generally dodge the penalty by hitting a safe harbor: pay in at least 90% of this year's tax, or 110% of last year's tax if your prior-year adjusted gross income topped $150,000 (IRC §6654). A surprise vest can blow past what last year's number protects.

Two clean fixes, both before December 31:

• Bump your W-4 withholding on your remaining paychecks. Withholding is treated as paid evenly across the year, so a late-year increase can retroactively patch earlier quarters — a quirk an estimated payment can't match.
• Make a fourth-quarter estimated payment through IRS Direct Pay if there aren't enough paychecks left to absorb it.

Closing the RSU withholding shortfall now is cheaper than financing it through penalties later.

Move 3: Sell enough at vest to actually pay the tax

The most expensive RSU mistake isn't the withholding gap. It's holding every share, paying the tax out of pocket, and ending up over-concentrated in one stock you can't sell freely during blackout windows.

Most plans default to "sell-to-cover," which liquidates just enough shares to satisfy the 22% withholding. If your real rate is 37%, sell-to-cover leaves you funding the other 15% from savings — while your net worth rides entirely on one ticker.

The fix is boring and correct: sell additional shares at vest to cover your actual marginal rate, not the default. There's almost no tax cost to selling right at vest, because your basis equals the vest-date value — the gain since vesting is roughly zero. You're not financing the IRS at concentration risk; you're paying it with the asset that created the bill.

Move 4: Donate appreciated vested shares instead of writing a check

If you give to charity anyway, stop donating cash. Donate the RSU shares that have appreciated since they vested.

Here's why it's strictly better. Donate shares held more than a year to a qualified charity or a donor-advised fund, and you generally deduct the full fair market value under IRC §170 — and you skip the capital gains tax you'd owe if you sold them first.

The math: You hold $50,000 of vested shares with a $30,000 cost basis. Sell them and you'd owe long-term capital gains plus the 3.8% net investment income tax on the $20,000 gain. Donate them instead and the $20,000 gain disappears, while you still deduct the full $50,000. A donor-advised fund lets you take the deduction this year and decide which charities get the money later.

Move 5: Don't let the 3.8% net investment income tax ambush you

The headline 37% bracket isn't the whole bill. High earners also pay the net investment income tax — an extra 3.8% under IRC §1411 on investment income once your modified AGI clears $200,000 single or $250,000 married filing jointly.

RSU income at vest is wages, so it isn't hit by the 3.8% directly — but it raises your MAGI, which can drag your other gains, dividends, and interest into NIIT range. And when you eventually sell shares you've held past vest, the gain on that sale is investment income squarely in NIIT territory.

This is the second surprise. The first is the withholding gap. The 3.8% is the one that quietly tacks onto every dollar of investment gain on top of your capital gains rate. Plan the timing of sales across tax years and you can keep MAGI under the line in the years it matters.

Move 6: If you also hold ISOs, coordinate AMT before you exercise

This is where do-it-yourself planning falls apart. If you hold incentive stock options alongside your RSUs, exercising and holding ISOs creates a "bargain element" that's invisible to your regular tax return but counts as income for the alternative minimum tax under IRC §56.

Stack a large RSU vest and an ISO exercise in the same year and you can trigger AMT you never saw coming — a second surprise on top of the withholding gap. The fix is sequencing: model the RSU income and the ISO exercise together, and sometimes split the ISO exercise across two calendar years to stay under the AMT crossover.

This is genuinely hard to model by hand, which is the entire case for getting a specialist involved before December — not in April.

Make your RSU year-end tax moves with a CPA who speaks equity comp

The reason these moves get missed isn't complexity. It's timing. Every one of them has to happen before December 31, and a generalist CPA you see once a year in tax season finds them too late to fix.

Anomaly CPA is featured on Sam's List for working with tech employees and founders on exactly this — RSU withholding gaps, ISO and AMT sequencing, and the year-end timing decisions that decide your April bill. They handle the messy parts too, like the common broker error where a 1099-B reports $0 cost basis on RSU sales and would have you taxed twice on the same income.

Read Anomaly CPA's verified reviews on Sam's List and book an intro call before your next vest — equity-comp tax planning works when there's still time to act on it, and on samslist.com you can find a CPA who does this every day, not once a year.

Want a quick number before you talk to anyone? Estimate the withholding gap with our free RSU tax calculator for your next vest.