The Retirement Tax Trap: RMDs, Roth Conversions, and the IRMAA Cliff

Most people spend their careers focused on accumulating money in tax-deferred accounts — 401(k)s, traditional IRAs, SEP-IRAs. The tax break is real and valuable. But the bill eventually comes due, and for many retirees, it arrives in a bigger way than expected.

Here is what to understand about the three tax forces that most affect retirement income.

Required Minimum Distributions: The Mandatory Withdrawal

The IRS does not allow you to keep money in a traditional IRA or 401(k) indefinitely. Starting at age 73 (under the SECURE 2.0 Act, effective 2023), you are required to take annual minimum withdrawals — called required minimum distributions (RMDs) — from your tax-deferred accounts.

The amount is calculated each year based on your account balance and a life expectancy factor from IRS tables. A simplified example: at age 73, the factor is roughly 26.5, meaning if you have $500,000 in traditional IRAs, your RMD is approximately $18,868 for that year.

Here is the problem: RMDs are fully taxable as ordinary income. If you have a large traditional IRA balance — $500,000, $1 million, or more — your mandatory withdrawals can push you into a higher tax bracket, make a larger portion of your Social Security taxable, and trigger Medicare IRMAA surcharges (more on that below).

The size of your future RMDs is determined largely by decisions you make before age 73. That window matters.

The Roth Conversion Opportunity

A Roth IRA operates differently from a traditional IRA: you contribute after-tax dollars, the money grows tax-free, and qualified withdrawals in retirement are completely tax-free. Roth accounts also have no required minimum distributions during your lifetime.

You can convert money from a traditional IRA to a Roth IRA at any time — you simply pay income tax on the amount converted in the year of conversion. This is where the strategy comes in.

For many retirees, the years between retirement and age 73 represent a low-income window. You may no longer have a salary. Social Security might not have started yet. RMDs haven't begun. Your taxable income can drop to the lowest level it has been in decades.

Converting traditional IRA money to Roth during this window means:

• §You pay tax at your current (lower) rate rather than a potentially higher rate later
• §Future growth on converted funds is tax-free
• §Your future RMDs are smaller (because the converted money is no longer in the traditional IRA)
• §Your heirs inherit a Roth, which they can draw from tax-free

The goal is not to convert everything at once. The goal is to convert up to the top of a target tax bracket each year — filling the bracket without crossing into the next one.

IRMAA: The Medicare Surcharge Most People Don't See Coming

Medicare Part B and Part D premiums are not flat fees for everyone. Higher-income beneficiaries pay more through Income-Related Monthly Adjustment Amounts (IRMAA).

IRMAA is based on your modified adjusted gross income (MAGI) from two years prior. In 2025, the standard Part B premium is $185.00/month. But if your 2023 MAGI exceeded $106,000 (single) or $212,000 (married filing jointly), you pay more — potentially hundreds of dollars more per month per person.

The thresholds are called "cliffs" because crossing one by even a dollar jumps you into the next surcharge tier. A large Roth conversion, a one-time property sale, or a high RMD year can unexpectedly push you over a threshold.

This is one reason why Roth conversion planning requires looking two years ahead — a conversion that looks smart in isolation may trigger IRMAA surcharges that partially offset the tax benefit.

The Core Takeaway

These three forces — RMDs, Roth conversions, and IRMAA — interact with each other in ways that are easy to underestimate. The decisions you make in the years between retirement and age 73 can have a compounding effect on your tax picture for the rest of your life.

The low-income years of early retirement are not just a pause before benefits kick in. For many people, they are the most important tax planning window they will ever have.