Severance and a Big Vest in the Same Year: Why April Can Surprise You

The email arrives on a Tuesday. Your role is eliminated. A separation agreement lands in your hands, offering severance pay alongside health continuation terms. Just months earlier, your scheduled restricted stock units (RSUs) vested. You assume the deductions on your pay stubs took care of the taxes. Then April arrives, and the balance due is a complete surprise.

When severance pay and an RSU vest happen in the same calendar year, standard withholding often falls short. Both payouts are supplemental wages under tax rules, meaning employers use flat withholding percentages rather than your true tax rate. Combining these income events pushes total compensation into higher brackets, creating an unexpected balance due when filing your return.

Why Supplemental Withholding Creates an April Shortfall

Supplemental wages include bonuses, commissions, severance pay, and restricted stock unit vesting under IRS Publication 15. For federal taxes, withholding on supplemental wages is a flat 22%, and a mandatory 37% on supplemental wages above $1 million in the year. California also applies flat supplemental withholding rates, alongside State Disability Insurance requirements outlined by the California Employment Development Department.

For high-income earners with base pay and equity compensation, marginal brackets reach 32%, 35%, or 37% federally. In California, the top bracket is 12.3%, plus a 1% surcharge on taxable income over $1 million (13.3% combined).

As discussed in why RSU withholding falls short, a flat 22% rate does not cover the full liability for an earner in higher brackets. When severance arrives after a significant vest, the withholding shortfall compounds. Severance is wages: income tax withholding, Social Security up to the wage base, and Medicare all apply. The gap between flat withholding and your actual combined tax rate accumulates across both payouts, leaving a substantial balance due in April.

Related reading on RSU tax planning: One Stock Is Most of Your Net Worth: Where the Tax Conversation Starts.

What a Roadmap Tax Strategist Looks at in a Vest and Severance Year

When an RSU vest and severance coincide, a Roadmap Tax strategist reviews several critical elements:

1. Marginal bracket positioning and wage thresholds: We evaluate how severance pay interacts with prior salary and vested equity. This includes reviewing whether wages cross thresholds for the 0.9% Additional Medicare Tax on wages above $200,000 single ($250,000 married filing jointly), and tracking whether cumulative wages reached the Social Security wage base of $184,500.

2. Equity basis reporting: When shares vest and sell, cost basis reporting on Form 1099-B can lead to reporting mistakes, as detailed in our guide on RSU cost basis on Form 1099-B. We verify that basis adjustments are tracked properly so income is not counted twice.

3. Separation timing: When a job change or layoff occurs late in the year, separation agreements often provide a signing window. We evaluate whether executing the agreement in December versus January shifts supplemental wage income into a different tax year.

4. Estimated tax safe harbors: Relying strictly on flat supplemental withholding can lead to underpayment penalties. A strategist calculates safe-harbor payment requirements under IRS Publication 505 and coordinates estimated tax payments before deadlines pass.

Questions Worth Bringing to a Strategist

Before executing separation paperwork, review these questions with a strategist:

• How will the combined vest and severance affect your federal and California tax brackets for the year?
• Did your employer stop withholding Social Security tax once your wages crossed the Social Security wage base of $184,500?
• Will the withholding shortfall on your supplemental wages trigger an underpayment penalty, and what quarterly adjustment avoids it?
• If you were also laid off with unvested RSUs, what are the tax implications of your remaining equity?
• If you begin consulting between jobs, how should your new quarterly estimates account for your severance payout?
• If you start a new role before the year ends, how do you manage the dual-payroll pitfalls covered in two employers in one year tax withholding?

This is the kind of situation a Roadmap tax strategist reviews with clients before the deadlines pass.

FAQ

Why did my employer withhold 22% on severance pay?

Federal rules classify severance as supplemental wages. Employers can use a flat 22% withholding rate on supplemental wages up to $1 million in a year, which is often lower than the marginal tax bracket of a high earner.

Are severance pay and RSU vests taxed as ordinary income?

Yes. Both severance and RSU vest income are treated as wages. They are subject to federal and state income taxes, Social Security tax up to the annual wage base, Medicare tax, and the 0.9% Additional Medicare Tax above statutory thresholds.

Can severance and an RSU vest push me into higher California tax brackets?

Yes. California taxes wage income as ordinary income up to a top bracket of 12.3%, plus a 1% surcharge on taxable income over $1 million. Receiving severance and an RSU vest in the same calendar year can push your total income into California's highest brackets.

How can I prevent underpayment penalties when severance withholding is too low?

You can avoid underpayment penalties by making estimated tax payments or adjusting withholding to meet IRS safe-harbor rules, which generally require paying 90% of the current year tax or 100% of the prior year tax (110% for high-income earners).

This article is for educational purposes only and does not constitute tax, legal, or investment advice.