Roth Conversion Calculator
A married couple, both 67, has $50,000 of IRA withdrawals and $40,000 of Social Security. Converting $50,000 to a Roth in 2026 costs them $6,708 of federal tax. That is 13.4% of the amount converted. Enter your own year. The calculator shows the cost, the room left in each bracket, and whether the conversion crosses a Medicare or marketplace cliff.
Rules and tables checked against the IRS sources on September 2, 2026. Corrections log.
What the same $50,000 conversion costs at three income levels
| Ordinary income before converting | Federal tax without | With the conversion | Cost of converting | Rate on the converted dollars |
|---|---|---|---|---|
| $30,000 | $0 | $7,484 | $7,484 | 15.0% |
| $50,000 | $3,176 | $9,884 | $6,708 | 13.4% |
| $90,000 | $8,684 | $17,571 | $8,887 | 17.8% |
Married filing jointly, both 67, $40,000 of Social Security, no capital gains, 2026 tables, standard deduction with the age additions and the senior deduction. Federal only.
The cost is not the bracket rate. At $30,000 of other income the conversion pulls more Social Security into taxable income and eats the senior deduction. The rate on the converted dollars ends above 12%, although the couple never leaves the 12% bracket. That is the arithmetic the bracket table hides, and it is why the calculator computes the whole return twice rather than multiplying by a rate.
The bracket is a ceiling you choose
On the $50,000 example, a conversion of $64,300 keeps ordinary taxable income inside the 12% bracket. $168,735 fills the 22% bracket and $355,050 fills the 24%. Which ceiling is right depends on one comparison. The rate you pay now, against the rate you expect when the money would otherwise come out: at 73 or 75 as a required distribution, or in your heirs' hands. Convert while now is lower than later. Stop at the bracket top where that stops being true.
Two cliffs the bracket table does not show
This is the part that costs people real money, and it should be read before the bracket is chosen. Both cliffs are all-or-nothing, and both are set by income in the year of the conversion.
Medicare premiums, two years later. Part B premiums for 2028 are set from 2026 modified adjusted gross income. Cross $218,000 on a joint return ($109,000 single) by one dollar and each spouse pays an extra $974 a year for Part B. A Part D surcharge comes on top. The next line, $274,000 joint, raises it to $2,435 a year each. The calculator prints the tier and the room left to the next one. It matters from age 63, because income at 63 sets the premium at 65.
The marketplace subsidy line, under 65. For 2026 coverage the premium tax credit ends at 400% of the poverty line: $84,600 for a household of two, $62,600 for one person. One dollar over and the whole credit is gone, not reduced. Marketplace income counts the entire Social Security benefit and tax-exempt interest, so it runs higher than AGI. Cost-sharing reductions on Silver plans stop earlier, at 250% of the line, $52,875 for two. Tick the marketplace box above and the calculator shows where your conversion lands against both lines.
Two smaller slopes sit inside the tax itself, and both are already in the figure above. Each dollar of conversion can make up to 85 cents of Social Security taxable. Above $150,000 joint ($75,000 single), the $6,000 senior deduction shrinks by six cents per dollar.
When a conversion is the wrong move
- You are under 59½ and would pay the tax out of the IRA. The withheld tax is a distribution, and the 10% additional tax applies to it. Pay the tax from a taxable account or do not convert.
- You need the converted money within five years and are under 59½. Each conversion carries its own five-year clock. Take the converted principal out before the clock ends and before 59½, and the 10% additional tax applies to it, although the income tax was already paid.
- Your heirs will be in a lower bracket than you are now. They pay the tax then, at their rate. Converting now pre-pays it at yours.
- This is a high-income year. A severance, a bonus, a property sale. The conversion stacks on top of all of it. Next year is usually cheaper.
- It crosses a cliff by a small amount. Convert up to the line this year and the rest next year. The cliffs are annual.
Before you convert, write down four numbers
Ordinary income received so far this year. The Social Security and gains you expect by 31 December. The bracket top you are converting to. And the Medicare threshold two years out, if you are 63 or older. Enter them above, convert to the figure the calculator gives, and keep the page. A conversion cannot be undone; recharacterization ended in 2018.
Two other questions decide more than the conversion does. What will the required minimum distribution be on the balance you do not convert? If you are under 59½ and need income rather than a tax move, is a 72(t) series the better tool?
Frequently asked questions
How much tax will I pay on a Roth conversion?
The conversion is added to your ordinary income for the year and taxed through the brackets, after deductions. A married couple, both 67, with $50,000 of IRA withdrawals and $40,000 of Social Security pays $6,708 to convert $50,000. A single 60-year-old with $40,000 of other income pays $8,350. Enter your own figures above.
What is the biggest Roth conversion mistake?
Crossing an all-or-nothing line by a few dollars: the Medicare IRMAA threshold two years before Medicare, or the marketplace subsidy line at 400% of the poverty level. The second is paying the tax from the IRA before 59½, which makes the withheld tax a penalized distribution.
What is the break-even point for a Roth conversion?
There is no single one. A conversion pays off when the rate you pay now is lower than the rate the money would face later, as a required distribution or in an heir's hands. If the two rates are equal, a Roth still wins on flexibility, because it has no required distributions. If your rate now is higher, it loses.
When should you not do a Roth conversion?
In a high-income year, when it crosses a Medicare or marketplace cliff, when you would pay the tax from the IRA before 59½, or when your heirs will be in a lower bracket than you.
Does a Roth conversion affect Medicare premiums?
Yes. Medicare sets Part B and Part D premiums from your modified adjusted gross income two years earlier, and a conversion is part of that income. The 2026 surcharge starts above $109,000 for a single filer and $218,000 for a joint return.
Does a Roth conversion count as income for ACA subsidies?
Yes, in the year of the conversion. For 2026 coverage the premium tax credit ends at 400% of the poverty line, which is $84,600 for a household of two. A conversion that takes you over it costs the whole credit.
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SavingsLast calculators are educational estimates. They assume a constant average return and steady inflation; real markets are volatile and sequence-of-returns risk can shorten how long money lasts. Nothing here is financial, investment, tax, or legal advice. Consult a qualified professional before making decisions.
Printed from https://savingslast.com/roth-conversion-calculator/ on . The figures reflect the inputs shown and the rules as published on that date.