Roth Conversion Calculator 2026: Marginal Rate by Income

The seven rules that read the same dollar

A calculator that shows only the bracket answers a smaller question than the one you are asking. Each rule below uses a different income definition, a different year or a different shape, and the 2026 numbers come straight from the documents named in the last column.

Source: Rev. Proc. 2025-32 sections 4.01, 4.03 and 4.14; 26 U.S.C. 86, 151(d)(5)(C), 1411 and 36B; SSA POMS HI 01101.010 and HI 01101.020; CMS 2026 Medicare Parts A and B fact sheet; Rev. Proc. 2025-25 section 3.01; 2025 HHS poverty guidelines (Federal Register). The Social Security base amounts and the NIIT thresholds are fixed in the statute and are not indexed.

Two details decide most of the arithmetic below. First, the Social Security formula works on provisional income, which is income plus half of the benefits: once it passes the adjusted base amount, up to 85% of the benefits are taxable, so each dollar of other income can add 85 cents of taxable benefits until the 85% ceiling is reached, and a dollar converted can add $1.85 to adjusted gross income (our reading of IRC 86(a)). Second, the senior deduction is reduced for each person, so a couple who are both 65 lose 12 cents of deduction per dollar of income in the band and the rate on ordinary income there is the bracket rate times 1.12; the same arithmetic is worked in our senior deduction guide.

The four profiles

We built the map for four households that differ in the rules they meet. All use the standard deduction, no state tax and a conversion that is taxable in full; incomes are round numbers of ours, not statistics. The conversion is added on top of the income shown.

Source: our assumptions. The federal tax before conversion is our arithmetic on Rev. Proc. 2025-32 and IRC 86.

How to read the maps below. The first column is how much has been converted so far in 2026, the second is the income (modified adjusted gross income, MAGI) at that point, the third is the all-in cost of each dollar converted in that range, and the last lists what is switched on. A range that includes a one-time jump (IRMAA or the ACA credit) shows the rate of that single $10,000 step, jump included. The CSV has every $10,000 step and the exact dollar where each line is crossed.

Map 1: the couple on Social Security

Both spouses are 66, with $60,000 of benefits and $30,000 of IRA, pension and interest income. Before any conversion their MAGI is $49,600 (taxable benefits are $19,600, the senior deduction is $12,000, taxable income is $2,100 and the federal tax is $210). Converting adds a dollar to AGI and part of a dollar of taxable benefits.

Source: our arithmetic on Rev. Proc. 2025-32, IRC 86, IRC 151(d)(5)(C), IRC 1411 and SSA POMS HI 01101.020 (2026 tables used as a stand-in for the 2028 premium year).

What the map shows. From the first dollar to a $36,942 conversion the benefits inclusion is still growing, so the 10% and then 12% brackets cost 18.5% and 22.2%. After the 85% ceiling the cost drops to 12.0% until the bracket moves to 22% at a $67,301 conversion. From $69,001 the senior deduction shrinks, and the rate on ordinary income is 24.64%. IRMAA tier 1 begins above $218,000 of MAGI, which is a $137,001 conversion; the $5,000 of interest makes the NIIT apply to the first $5,000 above $250,000.

Source: our arithmetic. The IRMAA amounts are for two people on Medicare and use the 2026 tables as a stand-in for 2028.

Map 2: the landlord couple with dividends

Both spouses are 66, with $48,000 of benefits, $40,000 of net rental income and $20,000 of qualified dividends and long-term gains. Before any conversion MAGI is $100,000 (taxable benefits $40,000, senior deduction $12,000, taxable income $52,500, federal tax $3,404). Their $60,000 of rental and investment income is net investment income for the NIIT. Rent and fund income in a return is why this profile has more layers: for how rent reaches the Social Security test, see our guide to taxable rental income and Social Security.

Source: our arithmetic on Rev. Proc. 2025-32, IRC 86, IRC 151(d)(5)(C), IRC 1411 and SSA POMS HI 01101.020.

The extra layer is the capital-gain rate. A conversion raises ordinary taxable income, and that pushes the $20,000 of gains up the stack: from a $45,601 conversion the gains begin to leave the 0% zone (taxable income of $98,900 joint), so each ordinary dollar also moves a dollar of gains into the 15% rate and the federal rate is 27.0%, then 30.24% once the senior deduction starts to shrink. The most expensive step in this profile is the $170,000 to $180,000 conversion, where tier 2 of IRMAA (a further $3,472.80) arrives together with the NIIT.

Source: our arithmetic. The NIIT in this profile applies to at most $60,000 of net investment income, so it adds at most $2,280 in total.

For the NIIT in detail, including what counts as net investment income for a landlord, see our net investment income tax guide.

Map 3: the 62-year-old early retiree on an ACA plan

Single, 62, no Social Security yet, $25,000 of net rental income. The household income for the ACA credit is 160% of the 2025 poverty guideline ($15,650). We assume a $13,200 benchmark premium (an assumption of ours, the same one used on our ACA subsidy cliff page), so the credit before any conversion is $12,035 and the federal tax is $890. There is no senior deduction and no Social Security. Medicare starts at 65 (our reading), so a 2026 return reaches no IRMAA premium for this profile.

Source: our arithmetic on Rev. Proc. 2025-32, IRC 36B and Rev. Proc. 2025-25 (2026 applicable percentages: 4.19% to 6.60% at 150% to 200% of poverty, rising to 9.96% from 300% to 400%).

Below the cliff the credit does not stay still: the expected contribution is a percentage of income that rises as income rises, so each dollar converted costs about 10 to 16 cents of credit on top of the 10% or 12% bracket, which is why the first three rows are 24% to 29% and not 12%. At a $37,600 conversion MAGI is $62,600, exactly 400% of $15,650, and the extra federal tax so far is $4,442 plus $5,070.04 of credit given up on the way. The next dollar costs the remaining $6,965.04 of credit: the step that crosses it costs 89.2% of the $10,000.

Source: our arithmetic. The credit is the benchmark premium minus the applicable percentage times income, and it is zero above 400% of the poverty guideline (IRC 36B(b)(2) and (c)(1)(A)). With Pub. L. 119-21 section 71305, taxable years beginning after December 31, 2025 have no cap on repaying advance credits, so a lost credit is a real cost.

Map 4: the widow or widower filing as single

Single, 70, $36,000 of benefits, $20,000 of IRA income, $15,000 of net rental income and $10,000 of qualified dividends and gains. This is the profile of someone whose spouse died and who now files with the single brackets; our widow's tax penalty guide compares the single and joint tables. Before any conversion MAGI is $74,150 (taxable benefits $29,150, senior deduction $6,000, taxable income $50,000, federal tax about $4,635).

Source: our arithmetic on Rev. Proc. 2025-32, IRC 86, IRC 151(d)(5)(C), IRC 1411 and SSA POMS HI 01101.020.

The first dollars are the most expensive ones. At the starting point a dollar converted adds $1.85 to AGI through the benefits inclusion, so the 12% bracket costs 22.2%, and the $10,000 of gains sits across the 0% limit of $49,450, so each dollar of ordinary taxable income moves another 15% of it into tax: 49.95% federal on the first $460 converted. Between a $460 and a $1,706 conversion the senior deduction also shrinks (52.95%); after the 85% ceiling the rate falls to 28.62% and then 23.32% in the 22% bracket. Three IRMAA tiers come in the first $100,000 of conversion because the single lines are half the joint ones.

Source: our arithmetic. The IRMAA amounts are for one person on Medicare and use the 2026 tables as a stand-in for 2028.

What each cliff costs per dollar you convert past it

A cliff is paid once in the premium year (IRMAA) or on the return (ACA), so the extra cost per converted dollar depends on how much more you convert once you are past the line. The tables spread the one-time amount over a conversion of the size shown (our arithmetic); add the points to the federal rate of the range.

Source: our arithmetic on SSA POMS HI 01101.020 and the CMS 2026 fact sheet (monthly Part B and Part D amounts times 12 times the number of people on Medicare).

Source: same as above, one person.

The tier 5 amounts ($1,161.60 for two people, $580.80 for one) start at $750,000 and $500,000, far above the incomes in this map. The ACA cliff does not spread this way, because above $62,600 there is nothing left to lose: past the line the cost is zero, and below it the whole $6,965.04 is at stake for one dollar. How the IRMAA tiers read a property sale instead of a conversion is on our IRMAA brackets page.

Room under each line, and what it costs

If you decide to stop at a line, this is the conversion that lands exactly on it, the extra federal tax on that conversion, and what one more dollar would add.

Source: our arithmetic on the profiles above. The extra federal tax includes the NIIT where it applies; it does not include the IRMAA or ACA amounts, which are in the last column.

What this map leaves out

• State income tax. Most states tax a conversion, some do not; none is in the numbers.
• 2027. We found no revenue procedure with 2027 brackets, standard deductions or capital-gain thresholds as of October 22, 2026, so all of this is 2026 law. A conversion made by December 31, 2026 belongs to the 2026 return (our Roth conversion guide has the rule and what happens if the value drops afterward).
• IRMAA for 2028. A 2026 conversion is read for premium year 2028, and SSA has not published the 2028 table. We use the 2026 lines (SSA POMS HI 01101.020).
• The ACA benchmark. $13,200 is our assumption; the credit is the benchmark premium minus the required contribution, so a lower benchmark means a smaller cliff and a higher one a larger cliff. Medicaid, state subsidies and plan choice are ignored.
• Itemizing, the qualified business income deduction, credits and the alternative minimum tax. Not modeled. Nor is any basis in the IRA from nondeductible contributions (see our guide on the pro-rata rule for a backdoor Roth).
• Where the tax is paid from. The map assumes the tax is paid from outside the IRA. Tax withheld from the IRA is itself a distribution (see the guide linked above).
• What happens to the money afterward. The five-year clocks and the effect on the heirs are in our Roth IRA 5-year rules guide.

Check your own number by hand

1. Write your 2026 income without the conversion: Social Security, pensions, IRA withdrawals, net rent, interest, dividends, gains.
2. Add the conversion and compute provisional income (income plus half of the benefits). Compare it with $25,000 and $34,000 (single) or $32,000 and $44,000 (joint) and apply the IRC 86 formula. The result is your AGI.
3. Subtract the standard deduction ($16,100 single, $32,200 joint, plus $1,650 per spouse aged 65 or older, or $2,050 if unmarried) and the senior deduction ($6,000 per qualified person minus 6% of MAGI above $75,000 or $150,000, not below zero).
4. Tax the ordinary part with the 2026 brackets, then the gains at 0%, 15% and 20% on top.
5. Add the NIIT: 3.8% of the smaller of your net investment income and your MAGI above $200,000 or $250,000.
6. Check your MAGI against the IRMAA lines (the return from two years later is the one SSA reads) and, if you buy an ACA plan, against 400% of poverty.
7. Repeat with the conversion $10,000 larger and subtract. The difference divided by $10,000 is your cost, and the CSV shows the pattern to expect.

What a reader can do with this

• Find your profile. The layers that apply to you are those whose income range contains your MAGI. If you have Social Security, begin with the benefits inclusion; if you are under 65 and buy a plan, begin with the 400% line.
• Price the line before you cross it. The table above gives, for each profile, the conversion that lands exactly on a line and the cost of one more dollar. A conversion that stops a dollar short of a line and one that goes $50,000 past it are different decisions, and the amortization tables show how the one-time amounts spread.
• Mind the calendar. A conversion made by December 31, 2026 is a 2026 conversion; the IRMAA effect arrives in 2028 and the ACA effect on the 2026 return. If a cliff is the issue, the events SSA accepts for a premium reduction are listed on our SSA-44 page.
• Re-run it when the numbers change. The 2027 brackets, the 2028 IRMAA table and the ACA benchmark for your county are the three inputs this page cannot know yet.
• Take your actual return to a CPA or an adviser before December 31, 2026. The round-number profiles are for understanding the shape; the decision depends on your own forms.

This is analysis of public documents, not investment, legal or tax advice.

FAQ

Sources, read and saved on October 22, 2026: Rev. Proc. 2025-32 (2026 inflation adjustments: sections 4.01, 4.03 and 4.14); 26 U.S.C. 86, 151, 1411 and 36B (Cornell LII, as amended through Pub. L. 119-21); Rev. Proc. 2025-25 (2026 applicable percentage table); 2025 HHS poverty guidelines (Federal Register FR Doc. 2025-01377); SSA POMS HI 01101.010 and HI 01101.020 (December 2, 2025); CMS 2026 Medicare Parts A and B premiums and deductibles fact sheet; Schedule 1-A (Form 1040) 2025. All tax figures for the profiles are our arithmetic.