What is a Roth conversion?

Moving money from a traditional IRA or 401(k), where every dollar is taxed when it comes out, into a Roth IRA, where qualified withdrawals are never taxed again. You pay ordinary income tax on the converted amount in the year you convert. There is no income limit and no cap on the amount, and once converted the money is never subject to required minimum distributions during your lifetime.

How much does a Roth conversion cost?

It depends on what is already on your return that year. For a married couple in 2026 with a $40,000 IRA draw and no other income, a $100,000 conversion costs about $12,360 in federal tax. The same conversion for the same couple once they collect $48,000 of Social Security costs about $17,607, and once required minimum distributions of $60,000 replace the draw it costs about $18,017. The calculator on this page runs your own numbers.

When is the best time to do a Roth conversion?

For most retirees, the years after the paycheck stops and before Social Security and required minimum distributions begin. For many households income is at its lowest then, so converted dollars fill the 10% and 12% brackets, and with no Social Security on the return yet there are no benefits for the conversion to drag into tax. Once benefits and RMDs arrive, the same conversion stacks on top of them and the real rate climbs.

Does a Roth conversion affect Medicare premiums?

Yes, two years later. Medicare sets your Part B and Part D premiums from the tax return you filed two years earlier. A 2026 conversion sets your 2028 premium. In 2026 the first surcharge line is $218,000 of modified adjusted gross income for a couple and $109,000 for a single filer, and crossing it by one dollar costs a couple about $1,949 more in Part B premiums for the year.

Does New York tax Roth conversions?

Yes. New York includes the converted amount in state income just as the IRS does. But if you are 59½ or older, New York's pension and annuity exclusion lets you shelter up to $20,000 per person of that conversion income, shared with any other IRA or private pension income that year. Social Security itself is never taxed by New York.

Roth conversions

The same $100,000 Roth conversion costs $12,360 or $18,017. The difference is when you do it.

A Roth conversion is taxed as income in the year you do it. What it costs depends on what else is on the return underneath it. This page shows the math, gives you a calculator that runs your own numbers, and answers the questions that decide whether, when and how much to convert. By Jim Swiech, CPA.

Updated September 5, 2026 · 2026 federal and New York figures

Quick answer

Convert in the years after your paycheck stops and before Social Security and required minimum distributions begin. That is when the low brackets are empty and a conversion costs the least.

Convert enough each year to fill your current bracket, not spill into the next one, and stay under the Medicare income line that sets your premium two years later. Then do it again next year.

What would a conversion cost you this year?

Enter what is already on your return. The calculator adds the conversion on top and shows the federal tax it causes, the real rate on the converted dollars, how much Social Security it drags into tax, and the Medicare surcharge it would trigger two years out. New York is a checkbox.

Your numbers

Roth conversion this year

The amount you'd move from a traditional IRA or 401(k) to a Roth.Other IRA / 401(k) withdrawals

What you'd take out anyway this year, including any RMD.Pension (annual)

Your Social Security (annual)

Enter 0 if you haven't claimed yet.Spouse's Social Security (annual)

Interest, dividends, other income

Your ageSpouse's ageLive in New York? Add the state layer

$10,604

Federal tax on the $100,000 conversion

10.6%

Real rate on the converted dollars

Printed bracket before converting: 10%

Extra Social Security pulled into tax

None. Benefits not affected.

Medicare IRMAA hit, two years from now

$78,000 of room before the next line

The converted dollars are taxed at 10.6%, not the 10% bracket you started in. Part of that is climbing into the next bracket; part is Social Security being dragged into taxable income.

Five conversion sizes, same facts

Convert	Federal tax	Real rate	IRMAA in 2 yrs
$25,000	$1,750	7.0%	$0
$50,000	$4,604	9.2%	$0
$100,000	$10,604	10.6%	$0
$150,000	$21,302	14.2%	$0
$200,000	$32,962	16.5%	$1,949

2026 federal law, including the $6,000 per-person senior deduction for ages 65+. Assumes ordinary income only, standard deduction, no dependents, and that IRMAA applies to each spouse 65 or older. Educational, not advice. Your return has more lines than this.

Three stages of retirement, one conversion, three bills

Take a married couple, both the same age, with a traditional IRA. Same $100,000 conversion at three points in their retirement. Everything below is 2026 federal law run through the same engine as the calculator above.

Married filing jointly, 2026. Stage 1: age 63, $40,000 IRA draw, no Social Security. Stage 2: age 68, same draw plus $48,000 of Social Security. Stage 3: age 76, $60,000 RMD plus the same Social Security.
Convert	Stage 1: before Social Security	Stage 2: Social Security flowing	Stage 3: RMDs stacked
$25,000	$2,660 (10.6%)	$4,950 (19.8%)	$3,096 (12.4%)
$50,000	$5,660 (11.3%)	$7,950 (15.9%)	$6,357 (12.7%)
$100,000	$12,360 (12.4%)	$17,607 (17.6%)	$18,017 (18.0%)
$150,000	$23,360 (15.6%)	$29,267 (19.5%)	$29,677 (19.8%)

Read across the $25,000 row. At 63 it costs $2,660, a real rate of 10.6%. At 68 the same $25,000 costs $4,950, a real rate of 19.8%, even though the couple started the year in the 10% bracket. The conversion pulled $17,800 of their Social Security into taxable income on its way through. That is the tax torpedo, and it is why the printed bracket is the wrong number to plan with.

Stage 3 is the one people miss. By 76 the IRS is already forcing $60,000 out of the IRA every year. The couple has no empty bracket left to convert into, and the same $100,000 costs $18,017. The window did not close with a bang. It closed because the room was used up before they got to it.

How much should you convert in a year?

Enough to fill the bracket you are in, and no more. In 2026 the 12% bracket for a married couple ends at $100,800 of taxable income and the 22% bracket ends at $211,400. For a single filer those lines are $50,400 and $105,700. Taxable income is what is left after the standard deduction, which in 2026 is $32,200 for a couple and $16,100 for a single filer, plus $1,650 per spouse aged 65 or older ($2,050 for a single filer), plus the new $6,000 per-person senior deduction that runs through 2028 and phases out above $150,000 of income for a couple.

The practical rule: figure out how much room is left below the top of your bracket after everything else on the return, convert that amount, and check that the result stays under the Medicare line that matters two years from now. Bigger is not better. A conversion that spills into the next bracket, or over an IRMAA line, is paying tomorrow's rate today.

The rules that trip people up

Medicare IRMAA and the two-year lookback. Medicare sets your Part B and Part D premiums from the tax return you filed two years earlier. A 2026 conversion decides your 2028 premium. The first 2026 line is $218,000 of modified adjusted gross income for a couple and $109,000 for a single filer. One dollar over it raises the standard $202.90 monthly Part B premium to $284.10, about $1,949 more for a couple over the year, before the Part D surcharge. The IRMAA page has every line.

The five-year rules. There are two. Each conversion starts its own five-year clock, and pulling converted principal out before that clock ends costs a 10% penalty, but only if you are under 59½. Once you are past 59½ that penalty no longer applies. The rule that still matters for retirees is the other one: earnings inside a Roth IRA are tax-free only once five tax years have passed since the first year you funded any Roth IRA. If you have never had a Roth, open and fund one now so the clock is running.

No undo. Since 2018 a conversion cannot be reversed. Size it right the first time.

Paying the tax from outside the IRA. If you withhold the tax from the converted amount, less lands in the Roth and, under 59½, the withheld portion is itself a taxable early distribution. Paying the tax from a bank or brokerage account keeps the whole conversion working.

New York. The state taxes the converted amount, but taxpayers 59½ and older can exclude up to $20,000 per person of it under the pension and annuity exclusion. The New York page runs the numbers.

When a Roth conversion is the wrong move

If your tax rate today is higher than the rate you or your heirs will pay when the money comes out, converting pays tax early for no gain. That describes people still working at peak earnings, people who plan to give the IRA to charity, and people whose retirement income will be modest enough that most withdrawals would fall in the 10% or 12% brackets anyway. It also describes any year a conversion would push you over an IRMAA line you would otherwise clear. The calculator will tell you.

The questions, one page each

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Quick answers

What is a Roth conversion?: Moving money from a traditional IRA or 401(k), where every dollar is taxed when it comes out, into a Roth IRA, where qualified withdrawals are never taxed again. You pay ordinary income tax on the converted amount in the year you convert. There is no income limit and no cap on the amount, and once converted the money is never subject to required minimum distributions during your lifetime.
How much does a Roth conversion cost?: It depends on what is already on your return that year. For a married couple in 2026 with a $40,000 IRA draw and no other income, a $100,000 conversion costs about $12,360 in federal tax. The same conversion for the same couple once they collect $48,000 of Social Security costs about $17,607, and once required minimum distributions of $60,000 replace the draw it costs about $18,017. The calculator on this page runs your own numbers.
When is the best time to do a Roth conversion?: For most retirees, the years after the paycheck stops and before Social Security and required minimum distributions begin. For many households income is at its lowest then, so converted dollars fill the 10% and 12% brackets, and with no Social Security on the return yet there are no benefits for the conversion to drag into tax. Once benefits and RMDs arrive, the same conversion stacks on top of them and the real rate climbs.
Does a Roth conversion affect Medicare premiums?: Yes, two years later. Medicare sets your Part B and Part D premiums from the tax return you filed two years earlier. A 2026 conversion sets your 2028 premium. In 2026 the first surcharge line is $218,000 of modified adjusted gross income for a couple and $109,000 for a single filer, and crossing it by one dollar costs a couple about $1,949 more in Part B premiums for the year.
Does New York tax Roth conversions?: Yes. New York includes the converted amount in state income just as the IRS does. But if you are 59½ or older, New York's pension and annuity exclusion lets you shelter up to $20,000 per person of that conversion income, shared with any other IRA or private pension income that year. Social Security itself is never taxed by New York.

Updated September 5, 2026. Reviewed by Jim Swiech, CPA.

Educational and general in nature. Not tax, legal or investment advice, and not a recommendation to convert. Figures are 2026 federal and New York amounts under the assumptions stated; your return has more lines than any example. Go Beyond Tax is a brand of Swiech Consulting LLC.