Updated July 28, 2026. Quick answer: Treat it as taxable. We could not identify a broad retirement exclusion in Massachusetts’s cited authority that would cover a conversion, so plan on the converted amount being ordinary income at the state level.
Confidence note: we could not locate authority granting an exclusion. Treat as taxable and verify.
Why a conversion is a different question from a withdrawal
Almost every state summary answers “how does Massachusetts tax retirement income?” That is a question about distributions. A Roth conversion is not a distribution in the ordinary sense — it is a voluntary election to recognise income now in exchange for tax-free growth later. Whether a state’s retirement exclusion reaches that election is a separate question, and it is the one that decides your bill.
Where we cannot find authority for an exemption, we say so rather than assuming one exists. Verify with a Massachusetts preparer before converting a large amount.
What Massachusetts does with the converted amount
State income tax: flat 5% plus 4% surtax on taxable income over ~$1,107,750 (2026, indexed) — effectively 2 brackets (5%/9%)
How Massachusetts treats IRA and plan income: Massachusetts state/local and U.S. government contributory pensions exempt (as are pensions from states with reciprocal treatment). Private pensions, 401(k), and traditional IRA distributions taxable at 5% (IRA/annuity basis from previously MA-taxed contributions recovered tax-free). Large lump sums can trigger the 9% surtax band.
What to ask a preparer about Massachusetts
Is there any exclusion I am missing that would reach conversion income?
Converting around a move
Converting in the year you move into Massachusetts is the case that catches people. Residency at the moment of conversion is what generally determines which state gets to tax it, so a conversion executed a week before a move and one executed a week after can produce different bills.
Four separate taxes change when you move, not one: income tax on withdrawals, treatment of Social Security, estate tax, and inheritance tax. A state that looks good on conversions can be worse on the other three.
The state bill is the smaller half
Whatever Massachusetts does, the conversion is federal ordinary income first. The federal bracket you land in, and whether the conversion pushes you over an IRMAA threshold two years later, will usually move more money than the state line does. The state answer tells you whether to convert here; the federal answer tells you how much to convert at once.
Paying the tax from outside the account matters more than either. Using converted dollars to pay the bill shrinks the balance that was the entire point of converting.
Sources
Authority: M.G.L. c. 62 § 2(a)(2)(E); Mass.gov: Tax Treatment of Government Pensions in Massachusetts; M.G.L. c. 65C, sec. 2A (as amended by St. 2023, c. 50).
Compiled from state statutes, session laws and revenue-department publications and adversarially verified in July 2026. Dataset confidence for Massachusetts: high.
This page states what the cited authority says. It is not tax advice, and a conversion large enough to matter is worth putting in front of a preparer who can see your whole return.