A Massachusetts RSU tax calculator estimates the federal + 5% Massachusetts flat tax owed on each vest (plus a 4% Fair Share surtax on household income over $1M). Default 22% federal supplemental withholding usually under-collects — the calculator below shows the dollar shortfall for your bracket.
Calculate RSU Withholding
Estimate your RSU tax withholding and net proceeds after vesting.
Try Calculator →Open the Massachusetts RSU tax calculator with these inputs prefilled →
How Massachusetts taxes your RSU vest
Massachusetts treats RSU income exactly like ordinary W-2 wages: when shares vest, the fair-market value on the vest date is added to your Form W-2 Box 1 in the year of vest, taxed at the flat 5% Massachusetts Part B individual income tax rate, and reported alongside federal withholding (IRS Publication 525). Massachusetts is a flat-tax state — not progressive — so your Massachusetts liability scales linearly with RSU income up to the Fair Share surtax threshold, which is $1,083,150 for 2025 (inflation-indexed annually, not a flat $1M). Above that, the surtax adds another 4%, pushing the top combined Massachusetts rate to 9%.
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%.
- Massachusetts supplemental withholding rate: 5% flat. Massachusetts does not publish a separate "supplemental" rate the way California or New York do — employers withhold at the same 5% rate that applies to all Massachusetts wage income, so the default state withholding and your actual state liability are usually identical below the $1M surtax threshold.
If your marginal federal bracket is higher than the 22% supplemental rate, your employer is under-withholding on the federal side — and you owe the difference at filing time. The Massachusetts piece typically washes below $1M, but the federal gap shows up on every MA vest.
Worked examples (Massachusetts, 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, single filer
Inputs: $130K salary, single filer, 100 RSUs vesting at $90 FMV ($9,000 RSU income).
Result:
- Federal withholding: $1,980
- Massachusetts withholding: $450
- Estimated total tax on the vest: $3,298.50
- Shortfall vs default withholding: $180
The 22% federal default closely matches the 24% federal marginal rate at this income level, so the federal gap is small — $180. Massachusetts is a flat tax below $1M, so default state withholding (5% × $9,000 = $450) equals the actual Massachusetts liability on the vest. No state shortfall.
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Example 2 — Mid-level IC, married filing jointly
Inputs: $210K salary, married filing jointly, 400 RSUs vesting at $130 FMV ($52,000 RSU income).
Result:
- Federal withholding: $11,440
- Massachusetts withholding: $2,600
- Estimated total tax on the vest: $15,378
- Shortfall vs default withholding: $476
Total household income is $262,000, which puts this couple in the 24% federal bracket. The 22% supplemental rate is close but still short by 2 percentage points on the RSU income. Massachusetts contributes a clean $2,600 (5% × $52,000), with no state-side gap — household income is well below the $1M Fair Share threshold.
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Example 3 — Senior IC, married filing jointly
Inputs: $360K salary, married filing jointly, 1,500 RSUs vesting at $210 FMV ($315,000 RSU income).
Result:
- Federal withholding: $69,300
- Massachusetts withholding: $15,750
- Estimated total tax on the vest: $122,938
- Shortfall vs default withholding: $30,485.50
This is where Massachusetts RSU earners get hurt. Total household income lands at $675,000, deep into the 35% federal bracket but still below the $1M surtax threshold. The employer withholds at 22%, so on $315,000 of RSU income the federal gap alone is $30,485.50. Massachusetts state tax is a clean $15,750 (flat 5%), and there's also an estimated $2,133.99 underpayment penalty if no quarterly estimate is made. Total owed at filing: about $32,619.49.
Run this scenario in the calculator →
Why employer withholding usually isn't enough in Massachusetts
The gap is almost entirely federal, not state — at least until you cross the Fair Share surtax line. Massachusetts's flat 5% rate means employer supplemental withholding lines up with actual state liability for every vest size, every filing status, and every income level below $1M. The federal supplemental rate, by contrast, is a fixed 22% — and the moment your total income crosses into the 24%, 32%, 35%, or 37% brackets, your employer is under-withholding on RSU income. Once household income tops $1M, Massachusetts adds a 4% surtax that default 5% state withholding does not pick up, opening a second gap on the state side.
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.
- Sell-to-cover at vest — if your broker offers it, this can absorb the federal gap automatically; the state gap (5%, or 9% above $1M) usually still needs separate action.
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 dwarf your Massachusetts state liability — and if you cross the $1M Fair Share threshold, the state surtax compounds the problem.
How the Massachusetts RSU tax calculator handles your vest
The Massachusetts calculator uses Massachusetts's actual 2025 flat 5% Part B rate from the Massachusetts Department of Revenue, not a generic state placeholder. Because Massachusetts has no progressive brackets below $1M, the state portion of the engine is a straight multiplication on vest-day RSU income — but the federal side still walks the full 2025 IRS bracket table for your filing status, which is where the real shortfall comes from. The 4% Fair Share surtax layers on automatically once household income crosses $1M.
Open the calculator with your inputs →
FAQ
Does Massachusetts charge a higher rate on RSU income than on regular salary? No. Massachusetts uses a single flat 5% Part B rate on all earned income, including RSU vesting income. The 4% Fair Share surtax only kicks in on household income above $1M — and even then, it applies to all income above the threshold, not just RSU income.
Why is my Massachusetts RSU shortfall usually zero? Because Massachusetts withholding (5% flat) equals Massachusetts liability (5% flat) on the RSU income below the $1M threshold. The shortfall you see on Massachusetts RSU vests is almost entirely federal — driven by the 22% supplemental rate being lower than your real marginal federal bracket.
Do I owe Massachusetts tax on RSUs that vest while I live out of state? Generally only on the portion attributable to Massachusetts workdays during the vesting period — sourcing rules apply. Verify your specific situation with the Massachusetts Department of Revenue and a CPA.
When does the 4% Fair Share surtax apply to my RSUs? The surtax applies to total taxable income above the 2025 threshold of $1,083,150 (indexed annually for inflation — it was $1,053,750 in 2024) — including RSU vest income on top of salary and any other Massachusetts-source income. If a large vest pushes your household income across that line, plan for the surtax with a quarterly estimated payment, because default 5% state supplemental withholding will not cover it.
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%).
- Massachusetts Revenue Department — state flat-tax rate, Fair Share surtax, and equity-comp guidance.
- EquityTax Massachusetts 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.