IRA to Roth Conversion: Rules, Taxes, and Strategies

A Roth conversion moves money from a Traditional IRA (or other pre-tax account) into a Roth IRA. You pay income tax now, but all future growth and qualified withdrawals become tax-free. It is one of the most powerful tax planning moves available — when the timing is right.

Key Takeaways

• You pay ordinary income tax on the converted amount in the year of conversion.
• There is no income limit — anyone can convert at any amount.
• Conversions cannot be undone (no recharacterization since 2018).
• Best when your current tax rate is lower than your expected future rate.
• Watch the pro-rata rule if you have both pre-tax and after-tax IRA balances.

How a Roth Conversion Works

1. You have money in a Traditional IRA, SEP IRA, SIMPLE IRA (after 2 years), or a 401(k) you have rolled over to an IRA.
2. You tell your brokerage to convert some or all of that balance to a Roth IRA.
3. The converted amount is added to your taxable income for the year.
4. You pay tax at your marginal rate.
5. Going forward, the Roth IRA grows tax-free and qualified withdrawals are tax-free.

There is no limit on how much you can convert in a year. However, converting too much at once can push you into a higher tax bracket, trigger the Net Investment Income Tax (NIIT), or cause the Social Security tax torpedo for retirees.

When a Roth Conversion Makes Sense

A conversion is most beneficial when your tax rate today is lower than your expected tax rate in retirement. Common scenarios:

• Low-income years: Sabbatical, job transition, early retirement before Social Security and RMDs begin. This is the foundation of the Roth conversion ladder.
• Market downturns: Converting when account values are depressed means you pay tax on a smaller amount. When the market recovers, the growth is tax-free.
• TCJA sunset risk: If current tax rates (10%–37%) revert to pre-TCJA rates after 2025, converting now locks in today’s lower rates.
• Reducing future RMDs: Converting pre-tax balances to Roth eliminates Required Minimum Distributions on that money, giving you more control over retirement income.
• Estate planning: Roth IRAs pass to heirs with tax-free withdrawals (though the 10-year distribution rule still applies under SECURE Act).
• Tax diversification: Having both Roth and Traditional balances gives you flexibility to manage your effective tax rate in retirement by choosing which account to draw from each year.

When a Conversion May Not Make Sense

• You are in a high tax bracket now and expect a lower one in retirement. Paying 35% now to avoid 22% later destroys value.
• You need to use IRA funds to pay the conversion tax. The tax should be paid from outside funds (taxable accounts) to preserve the full Roth balance.
• You are close to Medicare IRMAA thresholds. A large conversion can push your MAGI above the threshold, increasing Medicare premiums for the next two years.

The Pro-Rata Rule

If you have both pre-tax and after-tax (non-deductible) money in your Traditional IRAs, you cannot cherry-pick which dollars to convert. The IRS applies the pro-rata rule: conversions are treated as coming proportionally from pre-tax and after-tax balances.

Example: You have $90,000 in a Traditional IRA (pre-tax) and $10,000 from non-deductible contributions. Total = $100,000. If you convert $10,000, the IRS treats 90% ($9,000) as taxable and 10% ($1,000) as tax-free — not the $10,000 of after-tax money you might prefer.

Workaround: Roll pre-tax IRA funds into your employer’s 401(k) (if it accepts rollovers). This removes the pre-tax balance from the pro-rata calculation, letting you convert the after-tax portion cleanly. This is a key step in the backdoor Roth strategy. If you have nondeductible IRA contributions, tracking your basis on Form 8606 is essential.

Partial Conversions: Bracket Filling

You do not have to convert everything at once. “Bracket filling” means converting just enough to fill up your current tax bracket without spilling into the next one.

Example (2026, Married Filing Jointly):

• Your other taxable income is $150,000.
• The 24% bracket ends at $394,600.
• You could convert up to $244,600 and stay in the 24% bracket.
• In practice, most people convert a more modest amount to manage the cash flow for the tax payment.

Tax Reporting

Roth conversions are reported on:

• Form 1099-R from your IRA custodian (distribution from the Traditional IRA).
• Form 8606 if you have any non-deductible (after-tax) IRA basis.
• The converted amount appears as income on your Form 1040, Line 4b.

How sharper.tax Helps

sharper.tax analyzes your tax return to calculate your current marginal rate, identify bracket space available for conversions, and model the long-term impact of Roth conversions on your tax picture. We flag pro-rata rule issues and show you the breakeven point where a conversion starts paying off. For the full math behind choosing Roth vs. Traditional, see our side-by-side comparison. Roth conversions work best as part of a multi-year tax plan — and for those with employer plans, compare the Roth 401(k) option as well. Sophisticated tax planning used to require a high-end CPA — we make it available for free.

Sources

• IRS Topic 408: Roth IRAs
• IRS Publication 590-A: Contributions to IRAs
• IRS Publication 590-B: Distributions from IRAs
• IRS Form 8606 Instructions

The information above is educational and not tax advice.