The RSU and ESPP Playbook: Sell, Diversify, Don't Stockpile

Two different benefits, one common mistake

Restricted stock units (RSUs) and employee stock purchase plans (ESPPs) are the two most common ways tech and other public companies pay employees in equity instead of, or on top of, cash salary. They work completely differently under the tax code, get taxed at different times, and call for different decisions when the shares land in your account.

The mistake that shows up constantly, in forums where people compare notes on compensation, is treating both the same way: letting shares from either program pile up untouched, year after year, until a meaningful share of someone's entire net worth sits in a single company's stock. That's not a strategy. It's what happens by default when nobody makes an active decision. Here's how each program actually works, and a straightforward framework for what to do with the shares once you have them.

How RSUs are taxed

An RSU is a promise: your employer grants you a number of shares that vest, meaning you actually own them, on a schedule, typically over three or four years. Until a batch vests, you own nothing you can sell or that counts toward your net worth.

The moment a batch vests, the fair market value of those shares on the vesting date is treated as ordinary income, reported on your W-2, exactly like a cash bonus. You owe income tax on that value whether you sell the shares immediately or hold them.

Here's the part that catches people off guard. Employers are required to withhold federal tax on supplemental income like RSU vests at a flat 22% for the first $1 million of supplemental income in a calendar year, and 37% above that, per IRS withholding rules for supplemental wages. If your actual marginal tax bracket is higher than 22%, which is true for a lot of RSU recipients once you add vested RSU income to a base salary, the 22% withholding often isn't enough. You can end up owing a real, unexpected amount at tax time the following April, not because anything went wrong, but because the standard withholding rate was never calibrated to your full bracket.

A worked example. Maya earns a $175,000 base salary and has $60,000 in RSUs vest during the year, for $235,000 in total taxable income. Her employer withholds 22% of the $60,000, or $13,200, for federal tax on the vest. But because RSU income stacks on top of her salary, part of it lands in the 24% bracket and part crosses into the 32% bracket (using the IRS's 2026 single-filer thresholds, where the 24% bracket runs through $201,775 and the 32% bracket picks up above that). Doing the math on that blend, Maya actually owes closer to $17,000 in federal tax on the $60,000, roughly $3,800 more than what was withheld. She either needs to set aside the difference herself, make an estimated quarterly payment, or budget for a larger-than-expected bill in April. This gap is common enough that it's worth checking your specific numbers every year RSUs vest, rather than assuming withholding covered it.

Once vested, any further gain or loss between the vesting date and when you eventually sell is a separate, ordinary capital gain or loss, taxed under the usual short-term or long-term rules depending on how long you hold after vesting, not from the original grant date.

How ESPPs are taxed

An ESPP works differently. You elect to have a percentage of your paycheck withheld over an offering period, typically six months, and at the end of the period, the plan uses that money to buy company stock, usually at a discount off the market price. Under a qualified Section 423 plan, the maximum discount allowed is 15% off fair market value, and most plans use exactly that figure.

Many ESPPs also include a "lookback" feature, which lets the plan apply the discount to whichever is lower: the stock's price at the start of the offering period or its price at the end. If the stock rose over the six months, the lookback locks in the 15% discount against the lower, earlier price, which can push your effective discount well above 15% in a rising market. The IRS also caps how much stock you can purchase under a qualified ESPP at $25,000 worth per calendar year, valued at the start of the offering period.

Selling ESPP shares comes in two flavors for tax purposes. A "qualifying disposition" means you held the shares at least two years from the offering (grant) date and at least one year from the purchase date. Meeting both thresholds means only the lesser of your actual gain or the original grant-date discount is taxed as ordinary income, with the rest taxed at the more favorable long-term capital gains rate. A "disqualifying disposition," meaning you sold before meeting one or both holding periods, taxes the full discount amount as ordinary income in the year of sale, with any additional gain taxed as a capital gain (short-term if held under a year from purchase).

A worked example. David's ESPP buys shares at a 15% discount, with a lookback. The stock was $40 at the start of the offering period and $52 at the end. His purchase price is 85% of the lower price, $40, so he pays $34 per share for stock now worth $52, an effective discount of about 35% versus the current market price. If David sells immediately (a disqualifying disposition), the full $18-per-share difference between his cost and the sale price is ordinary income. If he instead holds for the required two years from grant and one year from purchase, only the original grant-date discount ($40 x 15% = $6 per share) is ordinary income, and the remaining gain is taxed at long-term capital gains rates, which for most earners sit meaningfully below their ordinary income bracket.

The concentration problem

Both programs share the same downstream risk: they pay you in your employer's stock, and if you never sell, your net worth becomes increasingly tied to a single company's fortunes, the same company your paycheck already depends on. If that company has a bad year, you can lose your job and a large chunk of your net worth at the same time, which is precisely the scenario diversification exists to protect against.

A common rule of thumb among financial planners is to keep any single stock, including employer stock from RSUs and ESPP shares, under 5% to 10% of your total investable net worth. Above that range, a single company's stock price swing can meaningfully move your entire financial picture in a way a diversified index fund never would. This isn't a judgment about the company. Even a company you believe in strongly is still one company, subject to risks (a bad product cycle, new competition, a leadership change, an entire sector falling out of favor) that a diversified portfolio spreads across hundreds of companies instead.

Applying this in practice. For RSUs, the most common and simplest approach among people who've thought it through is to sell shares as soon as they vest, or close to it, and immediately reinvest the proceeds into a diversified index fund. Because you already owe ordinary income tax on the full vesting value whether you sell or hold, selling immediately doesn't create additional tax owed; it just converts stock you already paid tax on into cash you can redeploy, typically with little or no capital gain or loss to report since the sale price is close to the vesting-date value.

For ESPP shares, the calculus includes the tax benefit of a qualifying disposition, so a common middle-ground approach is to sell most of a purchase soon after buying it, banking the discount as a real, close-to-guaranteed gain, while optionally holding a smaller portion to reach the qualifying holding period if the tax savings are worth the added stock-specific risk of waiting one to two years for a lower tax rate on a wager you're not fully in control of.

Putting a number on your concentration

The only way to know if you're over-concentrated is to actually calculate the percentage, not guess. Add up the current market value of all employer stock you hold, across RSU grants that have vested and ESPP shares you haven't yet sold, and divide by your total investable net worth (excluding illiquid assets like home equity, which isn't part of this specific risk calculation).

A worked example. Priya has $340,000 in a diversified 401(k) and brokerage accounts, plus $85,000 in vested RSU shares and $22,000 in ESPP shares she's holding for the qualifying disposition window, both in her current employer's stock. Her total investable assets are $447,000, and $107,000 of that, about 24%, sits in a single company. That's well above the 5% to 10% guideline, even though every individual decision (holding ESPP shares briefly for tax reasons, not immediately selling every RSU vest) seemed reasonable in isolation. Priya's next move isn't necessarily to sell everything at once, which could trigger a larger tax bill in one year than necessary, but to set a plan to sell down toward the target range over the next several vesting cycles rather than letting the balance keep growing by default.

Where this fits in your net worth

Employer stock from RSUs and ESPP shares is a real asset and belongs in your net worth calculation at current market value like any other holding, but it's worth tracking separately from your diversified investments so the concentration is visible rather than buried inside a single "brokerage account" line. Seeing employer stock as its own category, next to the rest of your asset allocation by life stage, makes it far easier to notice when it's crept up to a quarter of your net worth instead of the 5% to 10% most planners recommend.

A monthly update that tracks your employer stock as its own line, alongside your diversified holdings, turns concentration from an abstract risk into a number you actually see every month, which is usually enough to prompt selling down before it becomes a real problem rather than after.

Frequently asked questions

Should I sell my RSUs the moment they vest?

For most people, yes, or close to it. You already owe ordinary income tax on the vesting-date value whether you sell or hold, so selling immediately doesn't add tax cost, and it converts concentrated stock exposure into diversified holdings right away rather than adding to your position in a single company.

Is it worth holding ESPP shares for the lower tax rate?

It depends on how much concentration risk you're willing to carry for one to two years in exchange for a lower rate on part of the gain. A common approach is to sell most of each ESPP purchase soon after buying it and hold only a portion long enough to qualify, rather than holding the entire purchase and accepting the added stock-specific risk.

What counts toward the 5% to 10% concentration guideline?

The current market value of all employer stock you hold, from any source (vested RSUs, purchased ESPP shares, stock options you've exercised), as a percentage of your total investable assets, excluding illiquid assets like home equity that carry a different kind of risk entirely.

Does selling RSU shares right after vesting trigger a big tax bill?

Not usually beyond what you already owe. The ordinary income tax is due on the vesting-date value regardless of whether you sell. If you sell close to the vesting date, the sale price is typically close to that value, so there's little additional capital gain or loss to report on top of the income tax already withheld or owed.