The best time to do a Roth conversion is usually the window between when you retire and when your Required Minimum Distributions (RMDs) begin—roughly ages 60 to 73. During those years, your taxable income is often at its lowest, your tax bracket is temporarily smaller, and every dollar you move from a traditional IRA into a Roth IRA gets taxed at a bargain rate you may never see again. Miss that window, and you could end up paying more in taxes on your savings than you ever needed to—while also triggering higher Medicare premiums and making more of your Social Security benefit taxable.

What exactly is a Roth conversion, and why does it matter?

A Roth conversion simply means moving money from a traditional IRA (or 401(k)) into a Roth IRA. You pay income tax on the amount you convert in the year you do it—but after that, the money grows tax-free and you never have to take it out on the government’s schedule. Traditional IRAs, by contrast, require you to start taking out money at age 73 under RMD rules (Required Minimum Distribution rules), whether you need the cash or not. Those forced withdrawals count as taxable income, which can push you into a higher bracket, increase the portion of your Social Security that gets taxed, and even raise your Medicare premiums through a surcharge called IRMAA.

Why is the ‘gap years’ window so valuable for conversions?

Most retirees leave full-time work somewhere between 60 and 65. Social Security benefits are often delayed until 67 or 70 to maximise the monthly amount. RMDs don’t start until age 73. That creates a gap—sometimes a decade long—where your reportable income drops significantly. If you have $800,000 sitting in a traditional IRA and you do nothing during those years, you’re leaving a major tax-planning opportunity on the table.

Here’s a simplified example. Say you’re 65, you’re not yet drawing Social Security, and your only income is $20,000 a year from part-time work. The standard deduction for a single filer in 2026 is around $15,700, which means your taxable income is only about $4,300. The 12% federal tax bracket for single filers runs up to roughly $48,000 of taxable income. That means you could convert nearly $44,000 from your traditional IRA into a Roth and still stay entirely within the 12% bracket—paying just 12 cents of federal tax on every dollar converted. Do that for five or six years, and you’ve moved a substantial chunk of savings into a tax-free account before RMDs ever force your hand.

How do RMD rules in 2025 and 2026 affect your conversion strategy?

Under current law (updated by the SECURE 2.0 Act), RMDs begin at age 73. Starting in 2033, the age bumps up to 75. The IRS calculates your RMD each year by dividing your account balance by a life-expectancy factor. For a 75-year-old with a $1 million traditional IRA, that could mean a forced withdrawal of roughly $43,000—added straight onto your taxable income whether you wanted it or not.

If you’ve already done Roth conversions during your gap years, that $1 million balance is smaller, and so is your RMD. Smaller RMDs mean lower taxable income, which means a lower chance of your Social Security being taxed at the maximum rate and a lower chance of triggering Medicare IRMAA surcharges.

How much of Social Security is taxable—and can a Roth conversion make it worse?

Up to 85% of your Social Security benefit can be subject to federal income tax, depending on your “combined income” (your adjusted gross income plus any tax-exempt interest plus half your Social Security benefit). The threshold where taxation starts is just $25,000 for single filers and $32,000 for married couples—figures that haven’t been adjusted for inflation in decades, meaning more retirees cross them every year.

Large RMDs push your combined income up, which can flip more of your Social Security into taxable territory. A well-timed Roth conversion strategy—converting during low-income years before RMDs begin—keeps that combined income lower in your 70s and 80s, potentially saving thousands in taxes on benefits you already paid into for decades.

How do Roth conversions help you avoid Medicare IRMAA surcharges?

IRMAA stands for Income-Related Monthly Adjustment Amount. It’s an extra charge added to your Medicare Part B and Part D premiums if your income from two years ago exceeded certain thresholds. In 2025, the standard Medicare Part B premium is $185 per month. But if your income two years prior was above $106,000 (single) or $212,000 (married filing jointly), that premium jumps—sometimes by hundreds of dollars per person per month.

Because IRMAA looks back two years, a large RMD at 74 can trigger higher Medicare premiums at 76. Roth conversions done in your early 60s reduce future RMDs and help keep your income in retirement below those IRMAA cliff edges. It’s one of the most overlooked connections in retirement planning.

When should you claim Social Security to maximise your benefit?

The longer you wait to claim Social Security—up to age 70—the larger your monthly benefit. For every year you delay past your full retirement age (66 or 67 for most people), your benefit grows by about 8%. That’s a guaranteed, inflation-adjusted return that’s hard to beat anywhere.

Delaying Social Security also pairs beautifully with the Roth conversion strategy. While you’re living on savings and converting IRA money during your gap years, you’re simultaneously letting your Social Security benefit grow. When you do turn it on at 70, you have a larger, partially-tax-sheltered income stream—and a smaller traditional IRA that will generate lower RMDs. The whole picture works together.

What’s the one number most retirees forget to check before converting?

Before you convert a single dollar, calculate your projected income for the full year—including any part-time work, pension payments, dividends, and capital gains distributions from mutual funds. Many retirees plan a conversion carefully and then forget that their fund pays out a large capital gains distribution in December, nudging them into the next bracket. Run the numbers in October or November, when you have a clearer picture of your full-year income, so you can convert precisely the right amount without an unpleasant tax surprise.

Roth conversion planning isn’t just about avoiding taxes today—it’s about engineering a lower tax bill for the next 20 or 30 years. The math is quiet, patient, and almost always in your favor if you start before the RMD clock runs out.

Frequently Asked Questions

When should I claim Social Security to maximise my benefit?

Waiting until age 70 to claim Social Security gives you the largest possible monthly benefit—about 8% more for every year you delay past your full retirement age (66 or 67). If you’re in good health and can cover expenses from savings or part-time work in the meantime, delaying is almost always the higher-value choice over your lifetime.

How much of my Social Security benefit is taxable?

Up to 85% of your Social Security benefit can be taxed at the federal level, depending on your combined income (adjusted gross income plus tax-exempt interest plus half your Social Security). Single filers with combined income above $25,000 and married couples above $32,000 start to see some of their benefit taxed. Keeping other retirement income low—through Roth conversions, for example—can reduce how much of your benefit gets taxed.

What are the RMD rules for 2025 and 2026?

Under the SECURE 2.0 Act, Required Minimum Distributions from traditional IRAs and most workplace retirement accounts begin at age 73 in both 2025 and 2026. The RMD amount is calculated by dividing your prior year-end account balance by an IRS life-expectancy factor. Failing to take your RMD results in a 25% penalty on the amount you should have withdrawn (reduced to 10% if corrected promptly).

How do I avoid Medicare IRMAA surcharges?

IRMAA surcharges are added to your Medicare Part B and Part D premiums when your income from two years earlier exceeds certain thresholds—$106,000 for single filers and $212,000 for married couples in 2025. You can reduce your risk by managing taxable income in retirement through Roth conversions, careful timing of capital gains, and keeping RMDs as small as possible by converting IRA funds during lower-income years before age 73.

What is the Medicare Part B premium for 2025?

The standard Medicare Part B premium in 2025 is $185 per month per person. However, if your income two years prior was above the IRMAA thresholds, your premium can rise significantly—up to $628.90 per month at the highest income bracket. Most retirees pay the standard rate, but planning your retirement income carefully can ensure you stay below the surcharge thresholds.