You changed jobs partway through the year, and RSUs are vesting at both the old employer and the new one in the same calendar year. Each employer’s withholding looks right on its own pay stub. Combined, they can leave a balance due when you file.
- Why: each employer withholds on its own RSUs as if that were your only income for the year. It isn’t.
- The result: combine both W-2s, and part of your income can land in a higher bracket than either employer accounted for.
- The risk: a big enough gap can also trigger an underpayment penalty on top of the tax.
The short answer: both RSU grants are likely under-withheld
Most likely, yes, at both jobs. Each vest is taxed as ordinary income at the shares’ fair market value on the vest date and added to that employer’s W-2.
How employers withhold on a vest:
- Flat rate: employers commonly withhold federal income tax on that income at the 22% flat supplemental rate in IRS Publication 15.
- Aggregate method: some use this instead, which adds the vest to a regular paycheck and withholds as though that pay recurred all year.
Two employers’ worth of RSU income in the same year is what pushes part of your combined income into a bracket neither payroll system saw. Only the income above each threshold is taxed at the higher rate, not your entire paycheck, but the gap grows quickly once two W-2s are involved.
Why two RSU streams create a withholding gap
Neither payroll made a mistake. Each withholds only on the wages it pays.
Each employer withholds on its pay alone
Your old employer withholds only on what it paid you. Your new employer withholds only on what it pays you. Neither sees the other’s payroll, and neither sees a spouse’s income.
- Regular pay follows your W-4 and the graduated withholding tables.
- RSU income is usually withheld separately at the flat 22%, regardless of your other income.
Here is an illustration for a single filer with no other income who takes the 2026 standard deduction of $16,100:
| 2026 wages | Old employer | New employer | Combined |
|---|---|---|---|
| Salary | $90,000 | $110,000 | $200,000 |
| RSU vests | $60,000 | $90,000 | $150,000 |
| W-2 wages | $150,000 | $200,000 | $350,000 |
| RSU withholding (22%) | $13,200 | $19,800 | $33,000 |
A new job resets your withholding and Social Security
Your new employer’s payroll starts from zero. It calculates withholding on each paycheck as though that pay rate ran all year, and it has no record of your old W-2.
Salary withholding can come out close to right, but nothing in either system accounts for the RSU income stacked on top.
Social Security resets too. Each employer withholds Social Security tax up to the annual wage base, $184,500 in 2026, independently. In the example:
- Old employer: withholds 6.2% of $150,000, or $9,300, on the wages it paid.
- New employer: withholds 6.2% of $184,500, or $11,439.
That is $9,300 more than one person owes. The excess comes back as a credit when you file. In the example it offsets $9,300 of the $15,900 income tax shortfall, and you get none of it until then.
In the example, neither employer paid more than $200,000, so neither withheld it, and you still owe 0.9% of $150,000, or $1,350.
How to model your combined tax bracket before the next vest
Start with a projection that covers both jobs.
Add up every income source across both jobs for the year
Get one number for the whole year:
- From the old job: wages and RSUs vested to date.
- From the new job: base salary and expected RSU vests through year-end.
- Everything else: a spouse’s income, bonuses, and other equity or investment income.
What counts as taxable income walks through the pieces.
Compare your marginal rate to the 22% withheld
Your marginal rate is the rate on your next dollar of income, not your average rate across the year. For combined incomes in this range, it is usually 32% to 37%. Each vest’s withholding gap runs roughly your marginal rate minus the 22% withheld.
Run your own numbers with Nino’s RSU tax calculator, and see RSU tax withholding for how the withholding breaks down.
The withholding moves to make now
Once you know the size of the gap, you have two ways to close it.
Add extra withholding on your W-4
Ask your new employer to withhold an extra dollar amount from each paycheck, using line 4(c) on Form W-4. The IRS treats withholding as paid evenly across the year, so an amount added in October also counts toward the April, June, and September installments.
Or make a quarterly estimated payment
Pay the IRS directly with Form 1040-ES by the quarterly due date after each vest: April 15, June 15, September 15, or January 15.
Time the fix to your job change and each vest
- Set the W-4 amount when you start the new job.
- Recheck it after each vest rather than in December.
That spreads the extra tax across the paychecks left instead of one January payment. RSU tax withholding and sell-to-cover explains how each vest is funded.
What Nino does when RSUs vest at two employers
After a job change, who keeps your RSU plan current across both employers?
- Your old payroll stopped at its own paycheck.
- Your new payroll started from zero.
- Your CPA typically sees both W-2s only after January 31, once the year has closed.
- A financial advisor sees your portfolio, not necessarily your payroll.
No one in that setup sizes the W-4 change or the estimated payment while there is still time to make it.
Nino’s Advisor plans give you a human CPA and financial planner, and you enter both employers’ RSU grants in Nino’s grant form.
Plans start at $300/mo, billed annually, and include federal and state tax filing: the CPA prepares the return, and nothing is filed until you approve it. See current plans, or how Nino compares to other options.
Ask your current CPA or advisor who is sizing your W-4 change or estimated payment before your next vest. If nobody is, book a free consultation.