---
title: "Massachusetts RSU Tax Calculator (2026): Withholding, Shortfall, and Vesting Examples"
slug: ma-rsu-vesting-tax
publishedAt: 2026-06-16T17:00:07.000Z
updatedAt: 2026-06-17T16:41:54.788Z
author: "Mike Navarro"
authorSlug: mike-navarro
category: "State Tax"
tags: ["Massachusetts", "RSU", "Withholding", "Vesting", "State Tax"]
excerpt: "Massachusetts RSU tax calculator: federal 22% supplemental vs MA flat 5% (plus the 4% Fair Share surtax above $1M), three worked vests, and the dollar shortfall."
canonical: https://myequitytax.com/blog/ma-rsu-vesting-tax
---


<TaxYearBadge year={2025} />
<ReviewedBadge year={2025} />

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.

<CalculatorCTA calculatorType="rsu" />

[**Open the Massachusetts RSU tax calculator with these inputs prefilled →**](/calculator/rsu?state=MA&shares=100&fmv=90&salary=130000)

## 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](https://www.irs.gov/publications/p525)). 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](https://www.irs.gov/publications/p15)). 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.

[Run this scenario in the calculator →](/calculator/rsu?state=MA&shares=100&fmv=90&salary=130000)

### 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.

[Run this scenario in the calculator →](/calculator/rsu?state=MA&shares=400&fmv=130&salary=210000)

### 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 →](/calculator/rsu?state=MA&shares=1500&fmv=210&salary=360000)

## 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:

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.
3. **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.

<Callout type="warning">
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.
</Callout>

## 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 →](/calculator/rsu?state=MA)

## 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](https://www.mass.gov/topics/personal-income-tax) 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](https://www.mass.gov/topics/personal-income-tax) — state flat-tax rate, Fair Share surtax, and equity-comp guidance.
- EquityTax Massachusetts RSU Calculator (internal engine, last verified 2026-05-09).

<TaxDisclaimer />

*Estimate only — not financial or tax advice. Consult a qualified CPA before making decisions about exercising stock options, selling equity, or other financial moves.*