What Is a Roth Conversion?
A Roth conversion moves money from a traditional (pre-tax) retirement account — such as a Traditional IRA, 401(k), or 403(b) — into a Roth IRA. The converted amount is added to your taxable income for the year, but once the funds are in the Roth account they grow tax-free and qualified withdrawals are completely tax-free.
Why consider converting?
Roth conversions let you pay taxes now at a known rate instead of later at an unknown rate. If your current tax bracket is lower than what you expect in retirement, conversions can save significant money over time.
How the Tax Math Works
When you convert, the amount is treated as ordinary income stacked on top of your other income for the year. This means the converted dollars are taxed at your marginal rate.
| Scenario | Taxable Income Before Conversion | Conversion Amount | Marginal Rate on Conversion |
|---|---|---|---|
| Low-bracket year | $45,000 | $40,000 | 12% – 22% |
| Mid-career | $120,000 | $40,000 | 24% – 32% |
| High-income year | $250,000 | $40,000 | 35% |
The key insight is that the marginal rate on the converted dollars determines whether the conversion is beneficial. Converting in a year when your income is temporarily low (job transition, early retirement, sabbatical) can be especially advantageous.
The Retirement "Tax Window"
For many retirees, there is a window between retiring and age 72–75 (when Required Minimum Distributions begin) where taxable income drops significantly. This creates an ideal opportunity for systematic Roth conversions.
Before RMDs Begin
During this period you may have very little taxable income — perhaps just Social Security benefits or small pension payments. This allows you to convert at the lowest possible rates.
After RMDs Begin
Once RMDs start, they fill up your lower tax brackets automatically. Any Roth conversion then gets stacked on top of the RMD, pushing you into higher brackets and making conversion less efficient. Charitably inclined retirees can recapture some of that bracket space with Qualified Charitable Distributions, which satisfy the RMD without adding to AGI — preserving room for additional conversions in the same year.
IRMAA impact
Large conversions can push your Modified Adjusted Gross Income above IRMAA thresholds, increasing your Medicare Part B and Part D premiums two years later. Factor this cost into your conversion analysis.
Multi-Year Conversion Strategies
Rather than converting a large lump sum in one year (and paying high marginal rates), most advisors recommend spreading conversions across multiple years to stay within favorable tax brackets.
Bracket-Filling Strategy
This approach converts just enough each year to "fill up" a target tax bracket without spilling into the next one. For example, if the 22% bracket ends at $89,075 for a single filer and your other income is $35,000, you could convert approximately $54,000 while staying entirely in the 22% bracket.
Fixed-Amount Strategy
Convert a set dollar amount each year regardless of bracket boundaries. This is simpler to implement but may not be as tax-efficient.
Breakeven Analysis
A Roth conversion is beneficial if the tax savings from future tax-free withdrawals exceeds the upfront tax cost. Key variables include:
- Current marginal tax rate vs. expected future rate
- Investment time horizon (longer is better for Roth)
- Whether you can pay the tax bill from non-retirement funds
- State income tax considerations
- Impact on other income-sensitive provisions (IRMAA, ACA subsidies, Social Security taxation)
Pay taxes from outside the Roth
If you pay the conversion tax from the Roth account itself, you effectively reduce the amount that grows tax-free. Whenever possible, pay the tax from a taxable brokerage account or savings to maximize the long-term benefit.
Common Mistakes to Avoid
- Converting too much in one year — pushing into a high bracket or triggering IRMAA
- Ignoring state taxes — some states tax Roth conversions, others do not
- Forgetting the two-year IRMAA lookback — a large conversion in 2026 affects 2028 premiums
- Not coordinating with Social Security — conversion income can make up to 85% of Social Security benefits taxable
- Waiting too long — once RMDs begin, the window narrows significantly
Getting Started
A proper Roth conversion analysis requires projecting your income, tax brackets, and RMDs across multiple years. Work with a financial advisor who can model different scenarios and find the optimal conversion amount for your specific situation.
This article is for educational purposes only and does not constitute tax advice. Consult a qualified tax professional before making Roth conversion decisions.