---
title: "California RSU Tax Calculator (2026): Withholding, Shortfall, and Vesting Examples"
slug: ca-rsu-vesting-tax
publishedAt: 2026-06-16T17:00:02.000Z
updatedAt: 2026-06-17T16:41:54.729Z
author: "Mike Navarro"
authorSlug: mike-navarro
category: "State Tax"
tags: ["California", "RSU", "Withholding", "Vesting", "State Tax"]
excerpt: "California taxes RSU income at a top marginal rate of 13.3% and withholds at just 10.23% — see the gap for your bracket and run your numbers in 60 seconds."
canonical: https://myequitytax.com/blog/ca-rsu-vesting-tax
---
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.
[**Open the California RSU tax calculator with these inputs prefilled →**](/calculator/rsu?state=CA&shares=100&fmv=80&salary=120000)
## 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](https://www.ftb.ca.gov/file/personal/income-types/stock-options.html)).
The two numbers that matter on every vest:
- **Federal supplemental withholding rate:** 22% on RSU income up to $1M ([IRS Publication 15](https://www.irs.gov/publications/p15)). 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 →](/calculator/rsu?state=CA&shares=100&fmv=80&salary=120000)
### 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 →](/calculator/rsu?state=CA&shares=400&fmv=120&salary=225000)
### 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 →](/calculator/rsu?state=CA&shares=1500&fmv=200&salary=350000)
## 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:
1. **Adjust your W-4** so your paycheck withholding picks up the difference across the year ([IRS W-4 instructions](https://www.irs.gov/forms-pubs/about-form-w-4)).
2. **Make a quarterly estimated payment** if the shortfall is concentrated around a single vest date — California uses [FTB Form 540-ES](https://www.ftb.ca.gov/forms/2024/2024-540-es.pdf) on the same dates as the federal 1040-ES.
3. **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 →](/calculator/rsu?state=CA)
## 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](https://www.irs.gov/forms-pubs/about-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](https://www.ftb.ca.gov/file/personal/income-types/stock-options.html) — state supplemental withholding rate and equity-comp guidance.
- EquityTax California RSU Calculator (internal engine, last verified 2026-05-09).
*Estimate only — not financial or tax advice. Consult a qualified CPA before making decisions about exercising stock options, selling equity, or other financial moves.*