The most important thing to understand about Roth conversions is this: done at the wrong time or in the wrong amount, they can trigger a cascade of hidden costs — higher taxes on your Social Security benefits, expensive Medicare surcharges, and a bigger required minimum distribution bill down the road. Done right, however, a Roth conversion in your early retirement years can be one of the most powerful tax moves you’ll ever make. The math is not complicated, but most retirees miss three critical pieces of the puzzle — and this article walks through all of them.

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

A Roth conversion means moving money from a traditional IRA (or 401(k)) into a Roth IRA. You pay income tax on the amount you convert today, but from that point on the money grows tax-free and you never owe taxes on qualified withdrawals. There are also no required minimum distributions (RMDs) from a Roth IRA during your lifetime, which gives you far more control over your income in retirement.

The sweet spot for most retirees is the gap between when they stop working and when they start taking Social Security or RMDs — often ages 60 to 72. During those years, your taxable income may be unusually low, meaning you can convert at a lower tax rate than you’d face later.

How do Roth conversions interact with Social Security taxes?

Here is the piece most people miss first: converting money from a traditional IRA counts as income, and that income can make more of your Social Security benefit taxable.

Up to 85% of your Social Security benefit is taxable if your “combined income” (adjusted gross income + nontaxable interest + half of your Social Security benefit) exceeds $34,000 for single filers or $44,000 for married couples filing jointly. A Roth conversion that pushes you over those thresholds can trigger federal tax on benefits you may have assumed were tax-free.

This does not mean you should avoid conversions — it means you need to model the total picture. Convert just enough to stay below the threshold, or accept the extra tax hit only when the long-term savings clearly outweigh it.

As a general rule, delaying Social Security while you do Roth conversions is a smart pairing. Every year you wait past your full retirement age (up to age 70), your benefit grows by about 8%. That guaranteed, inflation-adjusted growth is hard to beat — and keeping Social Security income off your tax return during your conversion years gives you more room to convert at lower rates.

What are the RMD rules for 2025 and 2026, and why do they affect your conversion strategy?

Required minimum distributions are the IRS’s way of making sure you eventually pay tax on your traditional IRA money. Under current law (the SECURE 2.0 Act), RMDs begin at age 73. The amount you must withdraw each year is calculated by dividing your account balance by a life-expectancy factor published by the IRS.

Here is why this matters for conversions: every dollar sitting in a traditional IRA today is a future RMD waiting to happen. Large RMDs can push you into a higher tax bracket, increase your Medicare premiums, and make more of your Social Security taxable — all at once.

By converting portions of your traditional IRA in the years before RMDs kick in, you shrink the account balance that will eventually be subject to those mandatory withdrawals. Think of it as “draining the tank” while you can control the pace and the tax rate.

For 2026, the RMD rules remain at the age-73 starting point. There is no longer a penalty for missing an RMD in many cases if corrected quickly, but the missed distribution still gets added to your taxable income — so staying on top of deadlines matters.

How do Roth conversions trigger Medicare IRMAA surcharges?

IRMAA stands for Income-Related Monthly Adjustment Amount — it is the extra premium higher-income Medicare enrollees pay on top of the standard Medicare Part B and Part D premiums. For 2025, the standard Medicare Part B premium is $185.00 per month. But if your income two years prior exceeded certain thresholds, you pay significantly more — the surcharges can add hundreds of dollars per month per person.

The critical detail: Medicare looks at your income from two years ago. So your 2026 Medicare premiums are based on your 2024 tax return, and your 2027 premiums will reflect your 2025 income. A large Roth conversion in 2025 could push you into an IRMAA bracket in 2027.

The income thresholds for 2026 IRMAA surcharges (based on 2024 income) start at $106,000 for single filers and $212,000 for married couples filing jointly. There are five surcharge tiers above those levels.

This does not mean you should never convert if it triggers IRMAA — sometimes the long-term tax savings still win. But you must include the surcharge cost in your conversion math, not just the income tax rate.

How do I find the ideal conversion amount each year?

The goal is to fill up a tax bracket without crossing into the next one — or without triggering a Social Security tax cliff or an IRMAA tier jump. Here is a practical approach:

  1. Estimate your taxable income for the year from all sources (pension, part-time work, investment income, Social Security if you’re already collecting).
  2. Find the gap between that number and the top of your current tax bracket (or the nearest IRMAA threshold).
  3. Convert up to that gap — not a dollar more unless the math clearly favors it.
  4. Repeat annually and adjust as your situation changes.

A fee-only financial planner or a CPA who specialises in retirement tax planning can run these projections for you. Many retirees find that even modest conversions of $10,000 to $30,000 per year, done consistently for several years, dramatically reduce their lifetime tax burden and their heirs’ tax exposure.

Is a Roth conversion right for everyone?

Not necessarily. If you expect to be in a lower tax bracket in retirement than you are now, keeping money in a traditional IRA and taking distributions later may cost less overall. Conversions also make less sense if you would need to sell investments to pay the tax bill — ideally you pay conversion taxes from money outside the IRA.

But for the majority of retirees sitting on large traditional IRA balances — especially those with a pension, a spouse who will inherit the account, or a desire to leave tax-free money to children — the Roth conversion math almost always rewards those who run the numbers carefully.

The window between retirement and age 73 is genuinely one of the most valuable tax-planning opportunities available to you. The retirees who use it well often save tens of thousands of dollars over their lifetime. The ones who miss it usually wish they had started sooner.

Frequently Asked Questions

When should I claim Social Security to maximise my benefit?

Claiming Social Security at age 70 gives you the largest possible monthly benefit — about 24% to 32% more than claiming at your full retirement age (66 or 67, depending on your birth year). Delaying also pairs well with Roth conversions, since keeping Social Security off your tax return during conversion years gives you more room to convert at lower tax rates.

How much of Social Security is taxable?

Between 0% and 85% of your Social Security benefit may be subject to federal income tax, depending on your combined income (your adjusted gross income plus nontaxable interest plus half of your Social Security benefit). Single filers with combined income above $34,000 and married filers above $44,000 typically see 85% of their benefit taxed. Roth conversions count as income and can push you into or deeper into the taxable range.

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 for both 2025 and 2026. The annual amount is calculated by dividing your prior year-end account balance by an IRS life-expectancy factor. Roth IRAs are not subject to RMDs during the original owner’s lifetime, which is one of the key advantages of converting.

How do I avoid Medicare IRMAA surcharges?

IRMAA surcharges kick in when your income from two years prior exceeds $106,000 (single) or $212,000 (married filing jointly) based on 2026 thresholds. You can avoid or minimise them by managing the size of your Roth conversions, timing large income events carefully, and appealing to Medicare if your income has dropped significantly due to a life-changing event such as retirement or the death of a spouse.

What is the Medicare Part B premium for 2025?

The standard Medicare Part B premium for 2025 is $185.00 per month per person. Higher-income enrollees pay more through IRMAA surcharges, which can add anywhere from roughly $74 to over $443 per month on top of the standard premium, depending on income. These surcharges apply to both Part B (medical coverage) and Part D (prescription drug) premiums.