The california rsu tax calculator pairs the 22% federal supplemental rate with California's 10.23% supplemental rate against your real bracket — top CA marginal rate is 13.3%. For most mid-to-senior CA earners, employer withholding is short. Run your numbers below.
Calculate RSU Withholding
Estimate your RSU tax withholding and net proceeds after vesting.
Try Calculator →Open the California RSU tax calculator with these inputs prefilled →
How California taxes your RSU vest
California treats RSUs as ordinary wage income on the day they vest, exactly like a cash bonus. The fair market value of the shares on the vest date hits your W-2 in Box 1, and California withholds at its flat 10.23% supplemental rate — even though your real California marginal rate can climb all the way to 13.3% at the top.
That gap matters more in California than in any other state, because California has the highest state income tax in the country: a 1%–12.3% progressive bracket plus a 1% Mental Health Services Tax on income over $1,000,000, for a combined top rate of 13.3% (per the California Franchise Tax Board).
The two numbers that matter on every vest:
- Federal supplemental withholding rate: 22% on RSU income up to $1M (IRS Publication 15). Above $1M, the rate jumps to 37%.
- California supplemental withholding rate: 10.23%. California does not let employers vary this rate based on your bracket — they always withhold 10.23% on RSU vests, even if your true marginal rate is climbing toward the 12.3% or 13.3% top of the table.
If your marginal bracket is higher than the supplemental rate, your employer is under-withholding — and you owe the difference at filing time.
Worked examples (California, 2025)
These three scenarios use the EquityTax calculator with the inputs shown. The math is identical to what you'll see when you click through to the calculator.
Example 1 — Junior IC, $120K salary, single
Inputs: $120,000 salary, single filer, 100 RSUs vesting at $80 FMV (one vest, March 2025).
Result:
- Total RSU income: $8,000
- Federal withholding: $1,760
- California withholding: $818.40
- Estimated total tax on the vest: $3,276
- Shortfall vs default withholding: $85.60
At a 24% federal bracket and a 9.3% California bracket, employer withholding nearly matches the actual tax. There's a small federal shortfall of $160 because the bracket sits two points above the 22% supplemental rate, almost fully offset by California over-withholding. No estimated payment needed for a vest this size.
Run this scenario in the calculator →
Example 2 — Mid IC, $225K salary, single
Inputs: $225,000 salary, single filer, 400 RSUs vesting at $120 FMV.
Result:
- Total RSU income: $48,000
- Federal withholding: $10,560
- California withholding: $4,910.40
- Estimated total tax on the vest: $21,153.75
- Shortfall vs default withholding: $4,555.35
This is where the 22% federal supplemental rate falls apart. With $225K salary plus a $48,000 vest, you're firmly in the 35% federal bracket — so the 22% withholding leaves a $5,001.75 federal gap. California over-withholds slightly (–$446.40), but that doesn't cover the federal hole. Add the underpayment penalty of $318.87 and the total owed at filing is $4,874.22.
Run this scenario in the calculator →
Example 3 — Senior IC, $350K salary, MFJ
Inputs: $350,000 salary, married filing jointly, 1,500 RSUs vesting at $200 FMV.
Result:
- Total RSU income: $300,000
- Federal withholding: $66,000
- California withholding: $30,690
- Estimated total tax on the vest: $128,385.50
- Shortfall vs default withholding: $24,645.50
A $300,000 vest pushes a $350K-salary couple deep into the 35% federal bracket and the 9.3% California bracket. The 22% federal supplemental rate leaves a $27,435.50 federal shortfall. California over-withholds by $2,790, narrowing the net shortfall to $24,645.50. With a $1,725.19 underpayment penalty, total owed at filing is $26,370.69 — a quarterly estimated payment is essentially mandatory at this level.
Run this scenario in the calculator →
Why employer withholding usually isn't enough in California
California's 10.23% supplemental rate sits well below the 12.3% and 13.3% top brackets that kick in at higher incomes. Combine that with the federal 22% supplemental rate (which is below the 32%, 35%, and 37% federal brackets), and high-earning California RSU recipients almost always under-withhold.
The fix is straightforward and depends on the size of the gap:
- Adjust your W-4 so your paycheck withholding picks up the difference across the year (IRS W-4 instructions).
- Make a quarterly estimated payment if the shortfall is concentrated around a single vest date — California uses FTB Form 540-ES on the same dates as the federal 1040-ES.
- Sell-to-cover at vest — if your broker offers it, this can absorb the federal gap automatically; the state gap usually still needs a separate payment.
The 22% federal supplemental rate is a default — not your actual marginal rate. If your total income (salary + RSU) puts you in the 32%, 35%, or 37% bracket, the federal under-withholding alone can exceed the state shortfall.
How the California RSU Tax Calculator works
The California calculator uses California's actual 2025 brackets and the 10.23% supplemental withholding rate, not a generic state placeholder. It also separates default employer withholding (22% federal + 10.23% California + FICA) from the incremental tax you'll actually owe based on your full bracket — that's how it surfaces the shortfall figure that matters at filing time.
Open the calculator with your inputs →
FAQ
What is the California RSU withholding rate in 2025?
California withholds at a flat 10.23% supplemental rate on RSU income, the same rate it applies to bonuses and other supplemental wages. This is set by the FTB and does not vary by your tax bracket.
Why does my California RSU vest leave a shortfall at tax time?
Because the 22% federal supplemental rate and 10.23% California supplemental rate are both below the marginal rates of most mid-to-senior tech employees. If your combined federal + California bracket is 40% or higher, the default 32.23% withholding leaves a real gap.
Does California tax RSUs differently than federal?
The income event is the same — vesting triggers ordinary wage income at FMV under both rules. The difference is the rate: federal supplemental is flat 22% (or 37% above $1M of supplemental wages in a year), while California supplemental is 10.23%, and California's top bracket reaches 13.3%.
Should I make an estimated payment after a big RSU vest in California?
If your shortfall on a single vest is sizable, you're likely facing an underpayment penalty under IRS Form 2210 unless you cover it via a quarterly estimated payment (FTB Form 540-ES for California, IRS Form 1040-ES for federal). Run your scenario in the calculator above to see the exact number.
Sources
- IRS Publication 525, Taxable and Nontaxable Income — RSU treatment, fair-market-value rules.
- IRS Publication 15, Employer's Tax Guide — federal supplemental withholding rate (22% / 37%).
- California Franchise Tax Board — state supplemental withholding rate and equity-comp guidance.
- EquityTax California RSU Calculator (internal engine, last verified 2026-05-09).
Tax Disclaimer: This content is for educational purposes only. Always consult with a licensed tax professional or certified public accountant before making financial decisions related to equity compensation, tax planning, or investment strategies.
Estimate only — not financial or tax advice. Consult a qualified CPA before making decisions about exercising stock options, selling equity, or other financial moves.