How RSUs Work: Vesting, Withholding and Taxes

Alpha Sentinel is a software platform, not a registered investment adviser. This article is educational, not investment advice. Full disclaimer at the end of this post.

A vesting date lands on a Tuesday in the middle of a quarter-end push, and by Wednesday morning a block of shares has appeared in your brokerage account that you did not buy. A smaller number than you expected, too, because some were withheld. That is how restricted stock units, or RSUs, work in practice: a promise of shares that becomes real, and taxable, on a schedule your employer set long before. What follows is the sequence in plain terms, including the part that most often surprises people at tax time.

Key Takeaways

• An RSU is a promise to deliver company shares after a vesting condition is met, usually time or performance.
• You owe ordinary income tax at vesting on the market value of the shares delivered, and that amount appears on your W-2.
• Employers commonly withhold at a flat supplemental rate, which can be lower than your actual marginal rate.
• Your cost basis for later sales is the market value at vesting, so a subsequent gain or loss is measured from that date.
• A large vest can concentrate your portfolio in one employer, a risk that is separate from the tax.

1. What an RSU is, and what it is not

A restricted stock unit is a contractual promise from your employer to give you shares, or the cash equivalent, once a condition is met. Until then you do not own the shares: you cannot vote them, they carry no dividend in most plans, and you generally cannot sell them. This is different from a stock option, which gives you the right to buy at a set price. An RSU has no purchase price; the shares are simply delivered at vesting.

Because RSUs are delivered rather than bought, they have value as long as the stock is worth anything. That is a real difference from options, which can finish with no value when the market price sits below the exercise price. The tradeoff is that the tax treatment is less flexible: there is generally no election about when to recognize income.

2. How vesting schedules work

Most RSU grants vest on a calendar. A common structure is a multi-year schedule with a portion vesting at set intervals, sometimes with an initial cliff before the first portion vests. Some grants vest on performance goals instead, for example company results measured over a period. Your grant agreement and your equity plan document spell out the terms, including what happens if you leave, retire or are laid off before a vest date.

Two practical points. First, unvested units are generally forfeited if your employment ends, with exceptions your plan may carve out. Second, vesting is the moment the tax event occurs, so the calendar tells you when to expect income even though no cash arrives.

3. What happens to your taxes on the vest date

On the vest date, the fair market value of the shares delivered is treated as compensation. It is ordinary income, reported on your W-2 and subject to federal income tax, Social Security and Medicare taxes, and applicable state tax. The amount is the share count times the market price on that date.

Your cost basis in those shares is that same market value. That detail matters later: if you sell at a higher price, the difference is a capital gain, and if you sell at a lower price, a capital loss. Holding for more than a year after the vest date makes any gain long-term. Selling on the vest date typically produces little or no gain or loss because the sale price and basis are nearly the same. That is why the tax event and the investment decision are two separate things.

4. Why withholding often falls short

Employers must withhold tax on the vest, and many do it by withholding shares, a method called net share settlement or sell-to-cover. For federal income tax, supplemental wages are commonly withheld at a flat rate set by the IRS, with a higher rate applying to supplemental wages above a very large annual threshold. Check the IRS guidance on supplemental wages for the current figures.

The issue is that the flat rate is a withholding method, not your tax rate. If your marginal bracket is higher than the flat rate, your return may show a balance due even though tax was withheld. The gap tends to be most visible for higher earners and in years with several large vests. Common ways people handle it, all worth discussing with a qualified tax professional, include making estimated tax payments or adjusting other withholding. Self-directing and working with an advisor are both legitimate approaches.

5. The concentration question

RSUs add company shares to your portfolio each time they vest, which can leave a meaningful portion of your wealth tied to one employer. Your paycheck, your bonus and your equity may all depend on the same business, so a bad stretch for the company can hit several sources at once. That is a diversification issue, and it exists regardless of how the tax is withheld.

People take different approaches to this: some hold the shares, some sell at vest, some sell on a schedule. None of these is right or wrong in general; each depends on your goals, your other holdings and your tolerance for risk. What helps is deciding on a framework in advance and writing it down, rather than reacting on each vest date. Company trading windows and insider rules may also limit when you can sell, so check your employer's policy before assuming you can act on a given day.

6. An illustrative vesting day (not a forecast)

This hypothetical is meant to show the sequence, not an expected result. Picture an attorney-turned-executive with a quarterly vest. The day before, she looks at the number of units scheduled and the recent share price to estimate the pre-tax value of the vest.

On vest day, the company delivers a share count after withholding. She notes the fair market value used for withholding, which becomes her basis. A few days later she checks the pay statement and sees the full vest value added to her taxable wages for the year. Then she opens last year's return to compare the flat withholding rate to her actual marginal rate, and writes down a question for her preparer about estimated payments.

Finally, she looks at the position as a share of her total portfolio and decides, according to a rule she set earlier, how much she plans to hold. The rule is hers; the exercise shows that the tax steps and the portfolio decision happen separately and can be handled in order.

Frequently Asked Questions

When are RSUs taxed?

At vesting. The fair market value of the shares delivered is ordinary income on that date, and it appears on your W-2. Any later gain or loss on a sale is measured from that vest-date value.

Why was so much less than the full amount withheld on my RSUs?

Withholding is usually a flat supplemental rate, which may be lower than your actual marginal rate. If so, you can owe more at filing time, and some people use estimated payments to cover the gap.

What is my cost basis on RSU shares?

Your basis is the fair market value of the shares on the vest date. Broker statements sometimes report a different basis, so compare them to your W-2 and plan records to avoid paying tax twice on the same income.

Do RSUs get long-term capital gains treatment?

Only the gain after vesting can. The vest value is ordinary income, and any later appreciation is long-term if you hold the shares for more than a year after the vest date, otherwise short-term.

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