June 13, 2026 | Jonathan Bird
When Roth Conversions Hurt More Than They Help
Roth conversions are one of the most talked-about tools in retirement planning — and for good reason. In the right situation, they can save hundreds of thousands of dollars in lifetime taxes. But in 2026, four specific scenarios can quietly turn a smart move into an expensive mistake. If any of these apply to you, the standard Roth conversion playbook may be the wrong one.
1. The Medicare IRMAA Cliff
IRMAA stands for Income-Related Monthly Adjustment Amount — the mechanism by which Medicare calculates your premiums based on income. Cross just $1 over the next income threshold and your premiums rise for the entire year.
In 2026, Medicare Part B premiums can be as low as $23 per month per person — or as high as $690 per month. For a married couple, that's a potential difference of over $11,000 per year from a single dollar of income.
Here's the nuance worth knowing: Medicare uses a two-year lookback. Your 2027 premiums will be based on your 2025 income. That creates real planning opportunities — but also real landmines. If a Roth conversion pushes you over the next IRMAA threshold, the extra premiums you'll pay may erase the tax savings you were counting on. Sometimes the right move isn't avoiding conversions entirely — it's sizing them carefully to stay just below the next cliff.
2. Your RMDs Already Align With Your Spending
One of the most common fears I hear from clients approaching 73 is the prospect of required minimum distributions. The IRS forces those withdrawals and taxes them as ordinary income — so the intuition is to convert as much as possible beforehand to reduce the eventual RMD burden.
That instinct is understandable, but it can backfire. The key question is whether your projected RMDs, after taxes, will roughly match what you actually want to spend. If the answer is yes, doing Roth conversions on top of that means paying tax twice on the same dollars — once now to convert, and effectively at a higher bracket than necessary. In that scenario, conversions add no value and may actively cost you money. They may simply be worth skipping.
3. One-Time Income Events
Downsizing a home in retirement is common, financially sensible, and often frees up significant equity for spending. It's also a Roth conversion trap that catches a surprising number of people.
When you sell a home, the gain shows up on your tax return. The primary residence exclusion helps — $250,000 for single filers, $500,000 for married filing jointly — which makes the sale look relatively tax-friendly. The temptation then is to layer Roth conversions on top, since it appears you have room. But if the home sale gain and the conversion stack together, they can push you into a bracket that makes the conversion far more expensive than you anticipated. The exclusion doesn't make the income disappear entirely — it just removes one piece of it, and what remains can interact badly with a conversion.
4. The Tax Torpedo
This is the one that flies most under the radar — and it's the most counterintuitive.
The IRS uses a concept called provisional income to determine how much of your Social Security benefit is taxable. Provisional income equals all your taxable income, plus tax-exempt interest, plus half your Social Security benefit.
Here's how the thresholds work for married filing jointly:
- Under $32,000: 0% of Social Security is taxable
- $32,000–$44,000: 50% of Social Security is taxable
- Above $44,000: 85% of Social Security is taxable
Now here's where Roth conversions become a torpedo. Say you're in the 12% bracket and you convert $1 of IRA money. You'd expect to pay 12 cents in tax. But if that $1 pushes you above the $44,000 provisional income threshold, it drags 85 cents worth of Social Security from tax-free to taxable. Your effective tax rate on that conversion can jump from 12% to 22% — instantly, invisibly, and without any warning until April of the following year.
Two reasons this flies under the radar: most online calculators don't model it, and you won't see the damage until the tax bill arrives after the conversion is already done and irreversible.
When Conversions Still Make Sense
None of this means Roth conversions are off the table. For many retirees — especially those who retire early and have a meaningful gap between when earned income stops and when Social Security and RMDs begin — conversions can still be one of the most powerful tools available.
The point is that the math is no longer automatic. Each of these four traps — the IRMAA cliff, RMD alignment, one-time income events, and the tax torpedo — requires explicit modeling before pulling the trigger. A conversion that looks like a 12% rate can quietly become a 22% rate, and in some situations, no conversion at all is the better answer.
If you're unsure which camp you're in, the numbers are worth running before you act — not after.
