RSU 101: Sell or Hold? The Math

You Own Company Stock. Congratulations. Now What?

Your company gave you RSUs. They vested. Your brokerage account now shows a pile of your employer’s stock, and your HR portal is asking what you want to do with it.

Most engineers do one of three things: ignore the question until they’re forced to act, hold the stock because it feels like free money, or sell everything immediately and feel vaguely guilty about it.

Only one of those is mathematically defensible. Let’s work through why.

What RSUs Actually Are

RSU stands for Restricted Stock Unit. Your company grants you the right to receive shares of stock after you hit a vesting milestone — usually tied to tenure, sometimes to performance.

The grant date is when HR puts the number in your offer letter. That number is almost meaningless from a tax standpoint. The vesting date is when the shares actually become yours, and that’s when the IRS shows up.

A typical four-year vesting schedule with a one-year cliff looks like this: you vest nothing for 12 months, then 25% of your grant vests on the one-year anniversary, then the remaining 75% vests monthly or quarterly over the next three years. Every single vest event is a taxable moment.

The Part HR Glossed Over: You Already Paid for This Stock

Here’s the thing that changes your entire mental model of RSUs.

When your shares vest, the IRS treats the fair market value of those shares as ordinary income. Not capital gains. Not some future tax problem. Regular W-2 income, taxed at your marginal rate, right now.

Your company withholds taxes — usually via “sell-to-cover,” where they sell some of your vesting shares to cover the withholding. This happens automatically before you even see the shares in your account.

So here’s the reframe that matters: you didn’t get free shares. You got income in the form of shares. The same as if your company had paid you in cash and you immediately used that cash to buy company stock at today’s price.

That reframe is load-bearing. Read it again.

If your company had handed you $5,000 in cash and said “go buy our stock,” would you do it? That’s exactly the decision you’re making when you hold vested RSUs instead of selling.

The Math: Let’s Run the Numbers

Say 100 shares vest at $50/share. That’s $5,000 of gross income, added to your W-2 for the year.

Assume you’re in a high cost-of-living area, earning a tech salary, and your marginal rate (federal + state) works out to roughly 37%. That’s not a wild assumption for someone making $150k+ in California or New York.

Tax owed at vest: $5,000 × 37% = $1,850

Your company withholds this automatically, usually by selling shares. After withholding, you have the equivalent of about $3,150 in after-tax value — either as ~63 shares worth $50 each, or as $3,150 cash if you sold everything.

Now let’s say you hold those shares. The stock needs to go somewhere. Three scenarios (all figures are for the ~63 shares remaining after sell-to-cover withheld the $1,850 tax):

To break even versus just selling, the stock has to go up. To come out ahead versus a diversified index fund returning 7–10% annually, the stock has to beat that plus you’re taking on single-stock volatility.

And here’s the sneaky part: when you sell and realize the gain later, you’re only taxed on the appreciation above your vest price. Your cost basis in RSUs is the fair market value on the vest date — the amount you already paid income tax on. So a same-day sale is (usually) zero capital gains. A sale months later is taxed only on the move from $50 to wherever you sell. Hold for more than a year after vest and that gain becomes long-term, dropping the federal rate to 15–20% instead of your ordinary marginal rate — a real benefit, but only if the stock cooperates for 12+ months.

The math isn’t saying holding is always wrong. It’s saying holding is a bet, and you should be making it consciously.

Concentration Risk: You’re Already Betting on This Company

Here’s the argument most people miss.

Your job depends on your employer’s performance. If the company tanks, you lose your income, your unvested shares, and potentially your career momentum. You’re already heavily exposed to this one company.

When you hold vested RSUs instead of selling, you’re doubling down on that exposure. You now have financial assets and human capital riding on the same outcome. That’s concentration risk stacked on top of concentration risk.

A VP at a public tech company once told me he held 80% of his net worth in company stock because he “believed in the company.” A year later the stock dropped 60% in an earnings miss. His total wealth dropped by nearly half in 90 days, right as layoffs were announced. He believed in the company. The math didn’t care.

Diversification isn’t a hedge against success. It’s insurance against the variance that every single-company outcome contains — even good companies.

Sell-to-Cover vs. Same-Day Sale

Your brokerage probably offers you two options when shares vest:

Sell-to-cover: The company sells only enough shares to cover your tax withholding. You keep the rest in your account as shares. You still have to decide what to do with those remaining shares.

Same-day sale (sometimes called “sell all”): The company sells every share that vests. You get cash — minus taxes — deposited into your account or withheld from your paycheck.

A third option exists at some brokerages: hold — you keep all shares and pay the tax bill some other way (out of cash savings, or underpaying and making it up at tax time). This is how people end up in trouble. They hold, the stock drops, and now they owe taxes on income they no longer have as assets.

Sell-to-cover is the default at most companies and is fine — it covers the tax and lets you keep the upside if you’ve made a conscious decision to hold.

Same-day sale is simpler. You get cash, you diversify immediately, you never have to think about the basis of the remaining shares or when to sell them.

One practical note: if you use sell-to-cover and the tax withholding rate your company uses doesn’t match your actual marginal rate, you may owe more at filing. RSU income is taxed at your effective marginal rate, but companies often withhold at the flat supplemental rate (currently 22% federal). If you’re in the 32% or 37% bracket, you’re under-withheld. Plan accordingly.

When Holding Actually Makes Sense

To be complete: there are legitimate reasons to hold company stock.

You have strong conviction, and it’s a small percentage of your portfolio. If company stock is 5% of your net worth, holding it as a bet isn’t irrational. It’s a reasonable satellite position.

You’re in a low-income year — but only for the capital gains piece. To be clear: the ordinary income tax at vest is already owed and can’t be deferred by waiting to sell. What low-income-year timing can help with is the appreciation above your vest-price basis — if you’ve held past the 1-year LTCG threshold, selling in a low-income year might put you in the 0% long-term capital gains bracket on that gain. That’s a real but niche benefit, and it does nothing for the income tax bill that hit on day one.

You have an insider trading blackout or post-vesting lockup. Some employees can’t sell immediately due to trading windows. If that’s you, sell as soon as the window opens. Don’t let a temporary restriction become a permanent hold.

You genuinely believe the stock will significantly outperform the market. That’s your call to make. Just run the math first. Saying “I believe in the company” isn’t a return forecast.

The Verdict (Not Financial Advice, But Still Pretty Clear)

For most engineers, the rational default is: sell RSUs when they vest, reinvest in a diversified index fund.

You’ve already received the compensation. It was income at vest. The question now is purely: “Given a pile of cash, should I buy my employer’s stock?” And for most people, the honest answer is no — not because the company is bad, but because you’re already exposed to it in ways that don’t show up on your brokerage statement.

The math points one direction. Your emotional attachment to the company you work at points another. Both are real. Just be honest about which one is driving the decision.

Quick Reference

RSUs are good compensation. Don’t leave the value on the table by holding indefinitely out of habit or sentiment. The math is on the side of selling.