The 10-Year Window Most Retirees Miss. Here Is How Roth Conversions Work in 2026 — and Exactly When to Pull the Trigger.

WASHINGTON, May 30, 2026 —

The most common mistake in retirement tax planning is not paying too much in taxes on a single transaction. It is failing to see that the years between retirement and the start of Required Minimum Distributions represent a closing window during which the government lets you rewrite your entire retirement tax story at the lowest available rates.

A 62-year-old who retires with $1.2 million in a traditional IRA and no earned income suddenly has a problem that looks like the opposite of a problem. Their taxable income drops to near zero. Their tax bracket space is wide open. And every year they do nothing, that $1.2 million grows inside a tax-deferred account that will eventually force mandatory distributions at whatever tax rates apply when they turn 73 — distributions that will stack on top of Social Security income, investment dividends, and any other retirement income, potentially pushing them into brackets far higher than the ones available today.

The Roth conversion is the tool that resolves this problem. It is also the tool that, if misused, creates new ones.

How the 2026 Tax Brackets Create Specific Conversion Targets

The IRS adjusts tax brackets annually for inflation. The 2026 brackets, now permanently locked in under the One Big Beautiful Bill Act’s extension of TCJA rates, create specific dollar amounts that pre-retirees and retirees can target for annual conversions.

For single filers in 2026, the 12% bracket extends from $11,925 to $48,475. The 22% bracket runs from $48,475 to $103,350. The 24% bracket runs from $103,350 to $197,300. For married couples filing jointly, those thresholds approximately double: the 12% bracket tops at $96,950, the 22% bracket at $206,700, and the 24% bracket at $394,600.

The fill-the-bracket strategy uses these numbers as conversion ceilings. A retired couple with $60,000 in combined Social Security and investment income — taxable Social Security included — has $146,700 of available space in the 22% bracket before they cross into 24% territory. If they convert $146,700 of traditional IRA money this year, that entire conversion is taxed at no higher than 22%. If they wait until RMDs force distributions of $80,000 or $100,000 per year starting at 73, those mandatory distributions stack on top of Social Security and other income, potentially pushing significant portions into the 32% bracket.

The mathematics of converting at 22% now versus withdrawing at 32% later is not close. On a $100,000 conversion, paying 22% now costs $22,000 in tax. Withdrawing the same amount and its compounded growth later at 32% costs dramatically more — and the growth on the original $100,000 in a Roth account compounds tax-free for the entire intervening period.

The IRMAA Cliff — the Hidden Tax That Most Conversion Guides Miss

Here is where Roth conversions require precision that generic financial planning articles almost never provide. Medicare’s Income-Related Monthly Adjustment Amount — IRMAA — is a surcharge applied to Medicare Part B and Part D premiums for higher-income beneficiaries. The surcharge is determined using a two-year lookback: your 2026 income will determine your 2028 Medicare premiums.

For 2026, the IRMAA threshold for Part B premium surcharges begins at modified adjusted gross income above $106,000 for single filers and $212,000 for married couples filing jointly. A retiree who triggers the first IRMAA tier pays $70.90 more per month per person in Part B premiums in 2028 — an additional $1,702 annually per person, or $3,403 for a married couple on Medicare. Crossing the second IRMAA tier at $133,000 single/$266,000 married adds $178.60 per person per month.

A Roth conversion that pushes total income $5,000 above the IRMAA threshold could cost $3,400 in additional Medicare premiums over two years — premiums the retiree will pay even if the money converted is now growing tax-free in a Roth. The conversion math must account for this exposure. A $100,000 conversion that crosses the IRMAA line costs more than its stated marginal tax rate implies. The net effective rate on that final dollar of conversion may be 22% plus the IRMAA premium impact, which on small excess amounts can push the effective rate substantially higher.

The practical implication: conversion amounts should be sized to the nearest IRMAA threshold, not simply to the nearest tax bracket ceiling.

The Pro-Rata Rule — the Trap That Catches Most People Attempting Backdoor Conversions

For high earners who are also attempting backdoor Roth IRA contributions — making nondeductible IRA contributions and then converting them — the pro-rata rule is the mechanism that can turn a tax-efficient move into a taxable surprise.

The IRS does not allow a taxpayer with pre-tax IRA balances to convert only the after-tax portion of their IRA while leaving the pre-tax portion untouched. Instead, every conversion is treated as a proportional mix of after-tax and pre-tax dollars based on the ratio of after-tax basis to total IRA value across all traditional, SEP, and SIMPLE IRAs held by that individual.

A taxpayer who makes a $7,500 nondeductible IRA contribution in 2026 intending to convert it and who also holds $142,500 in a traditional IRA from prior pre-tax contributions has a total IRA value of $150,000, of which $7,500 — or 5% — is after-tax. A conversion of $7,500 will be 95% taxable under the pro-rata rule. The $7,125 taxable portion is not the clean, tax-free backdoor conversion the taxpayer intended.

The solution for affected taxpayers is to roll existing pre-tax IRA balances into a current employer’s 401(k) before executing the backdoor conversion, removing the pre-tax pool from the pro-rata calculation. Many 401(k) plans accept incoming rollovers. Confirming this option with the plan administrator before executing a backdoor strategy is the step most people skip and the step that determines whether the strategy works as intended.

The RMD Compression Problem — and Why the Window Closes Faster Than People Expect

Required Minimum Distributions begin at age 73 for most Americans under current law — age 75 for those born 1960 or later under SECURE 2.0. The amount of each annual RMD is calculated by dividing the prior year-end account balance by an IRS life expectancy factor. On a $1.2 million IRA at age 73, the first RMD is approximately $45,000. By age 80, if the account has grown, the annual RMD may exceed $80,000.

Those mandatory distributions are not optional. They do not care whether the retiree needs the money. They arrive each year and add to taxable income whether the retiree wants additional income or not. Stacked on Social Security — up to 85% of which becomes taxable above certain income thresholds — and other retirement income sources, the RMD can push a retiree’s effective tax rate significantly higher than the rate available during the pre-RMD window.

The conversion strategy that most efficiently compresses this problem involves converting enough each year during the pre-RMD window to reduce the traditional IRA balance to a level where future RMDs produce a manageable annual tax impact. A $1.2 million IRA reduced to $400,000 through a decade of strategic conversions produces RMDs of approximately $15,000 per year at age 73 — a number that, added to Social Security and other income, may still fit comfortably within the 22% bracket. The $800,000 that was converted and is now growing tax-free in the Roth account generates no RMDs ever.

Pro Tips a Generic Article Would Miss

1. The single highest-value conversion year for most retirees is often Year One of retirement — before Social Security begins and before any other income source resumes. A newly retired 62-year-old who delays Social Security until 67 has five years of near-zero ordinary income. In those years, the 22% bracket is almost entirely available for conversions. A $100,000 conversion in Year One of retirement — taxed at an effective rate that may be closer to 15% than 22% because the first dollars of income fill the 12% bracket and the standard deduction — represents one of the most tax-efficient transactions available in the American tax code. Most retirees spend Year One of retirement enjoying their freedom. The advisors who serve them well spend Year One executing the conversion plan that Year One’s low income makes possible.

2. The two-year IRMAA lookback means that conversion decisions made in 2026 create Medicare premium consequences in 2028 — and most retirees do not discover this until the premium notice arrives. The Social Security Administration sends a determination letter informing Medicare beneficiaries of their IRMAA surcharge determination for the coming year, based on income from two years prior. A retiree who executed a large Roth conversion in 2026 and forgot about the IRMAA threshold will receive a 2028 Medicare premium notice that is $1,700 to $7,000 higher than they expected, with no recourse available after the fact. The conversion was made. The tax was paid. The IRMAA surcharge is now an additional cost that compounds the effective rate on the conversion in retrospect. Sizing conversions to IRMAA thresholds — not just tax brackets — is the discipline that prevents this outcome.

3. Roth conversions reduce the taxable estate — a benefit that becomes most significant for heirs subject to the 10-year distribution rule under SECURE 2.0. Under the SECURE 2.0 Act, most non-spouse beneficiaries who inherit a traditional IRA must withdraw all funds within 10 years of the original owner’s death. If those withdrawals fall during the beneficiary’s peak earning years, they are taxed at the beneficiary’s highest marginal rate — potentially 32% or 37% on large inherited balances. A Roth IRA inherited by a non-spouse beneficiary under the same 10-year rule produces tax-free withdrawals for the entire 10-year period. The strategic implication is that a pre-retiree who converts pre-tax IRA money to Roth is not just reducing their own future tax burden. They are permanently eliminating the tax burden their heirs would otherwise face on the same dollars — at the heirs’ highest income rates, not the pre-retiree’s lower retirement rates.

FAQ

Q: What is a Roth IRA conversion and how does it work? A: A Roth conversion is the process of moving money from a traditional IRA, 401(k), or other pre-tax retirement account into a Roth IRA. The converted amount is added to your taxable income for the year of conversion and taxed at your ordinary income rate. Once inside the Roth, the money grows tax-free and qualified withdrawals in retirement are completely tax-free. There is no income limit on Roth conversions — anyone can convert any amount at any time, regardless of how much they earn.

Q: When is the best time to do a Roth conversion in 2026? A: The highest-value window for most Americans is between retirement and the start of Required Minimum Distributions — typically ages 60 to 73 or 75. During this period, ordinary income is often at its lowest, bracket space is most available, and conversions can be executed at the lowest effective rates before RMDs force mandatory distributions at higher rates. Conversions must be completed by December 31 of each tax year to count for that year.

Q: How much should I convert in a Roth conversion? A: The amount depends on your current year’s income, your tax bracket ceiling, and the IRMAA thresholds that affect future Medicare premiums. The fill-the-bracket approach converts enough each year to reach the top of your current bracket without crossing into a higher one. For a married couple with $60,000 in combined retirement income, the remaining space in the 22% bracket is approximately $146,700 — that is the maximum conversion that keeps every dollar taxed at 22% or lower in 2026.

Q: Does a Roth conversion affect Medicare premiums? A: Yes, with a two-year delay. Your 2026 income — including any Roth conversion amounts — determines your 2028 Medicare Part B and Part D premiums through the IRMAA system. If a 2026 conversion pushes your modified adjusted gross income above $106,000 for a single filer or $212,000 for married couples, your 2028 Medicare premiums will increase by $70.90 per person per month above the base rate. Larger income amounts trigger higher surcharge tiers. Conversions should be sized to stay below the nearest IRMAA threshold.

Q: Can I undo a Roth conversion if I change my mind? A: No. The Tax Cuts and Jobs Act of 2017, made permanent under the One Big Beautiful Bill Act, eliminated the ability to recharacterize — undo — Roth conversions. Once a conversion is executed and the tax year closes, it is permanent. This makes precise pre-conversion planning more important than it was under prior law, when a poorly timed conversion could be reversed before the tax filing deadline.

The five-year window between 62 and 67, for a retiree who delays Social Security to maximize their lifetime benefit, is the single most tax-efficient stretch of years most Americans will ever experience. Tax brackets are wide open. Social Security has not started. RMDs have not begun. The rate available on a Roth conversion during this window — potentially 12% or 22% on every dollar — is almost certainly lower than the rate their heirs would pay on the same money, or the rate they themselves would pay once RMDs arrive. The window is real, it is time-limited, and it closes at 73 whether the planning was done or not. Every December 31 that passes without a conversion is a year of that window that cannot be recovered.