Roth Conversion Optimizer

What is a Roth conversion?

A Roth conversion is the process of moving money from a pre-tax IRA or 401(k) into a Roth IRA. You pay income tax on the converted amount now, but the money then grows tax-free and is not subject to Required Minimum Distributions (RMDs) during your lifetime. Roth accounts also pass to heirs income-tax-free, making them a powerful estate planning tool.

How much should I convert to Roth each year?

The most common strategy is the fill-to-bracket approach: convert exactly enough each year to bring your taxable income to the top of a target bracket — for example, the 12% or 22% bracket. This maximizes the amount converted at lower rates without accidentally crossing into a higher one. This calculator computes that amount automatically for every year of your conversion window using 2026 federal brackets.

Why is the period between retirement and RMDs the optimal conversion window?

Once you retire and before Social Security and Required Minimum Distributions kick in, your taxable income often drops to its lowest point in decades. This gap — the years after you retire and before RMDs begin at age 73 (75 if born in 1960 or later) — creates a window where your marginal tax rate is low, sometimes 12% or even 0%, making it the ideal time to convert pre-tax dollars to Roth at a low rate.

Once RMDs begin at age 73 (or 75 if born 1960 or later), you must take distributions whether you need them or not. These are taxed as ordinary income, often pushing you into higher brackets. Converting before RMDs reduces the pre-tax balance that RMDs are calculated on, shrinking future forced withdrawals permanently.

How do Roth conversions reduce RMDs?

Required Minimum Distributions are calculated each year by dividing your pre-tax IRA and 401(k) balances by an IRS life-expectancy factor (the Uniform Lifetime Table). Every dollar you convert to Roth before age 73 is a dollar removed from that calculation. This calculator projects your full RMD schedule — year by year from age 73 onward — both with and without your conversion plan, so you can see exactly how much each year's forced withdrawal shrinks.

What is IRMAA and how do Roth conversions affect Medicare premiums?

IRMAA (Income-Related Monthly Adjustment Amount) is a surcharge added to Medicare Part B and Part D premiums when your Modified Adjusted Gross Income (MAGI) exceeds certain thresholds. In 2026, the first surcharge kicks in at $109,000 for single filers and $218,000 for married filing jointly. IRMAA is assessed two years after the income year — so a large Roth conversion in 2026 could raise your Medicare premiums in 2028.

Each IRMAA tier adds hundreds of dollars per month in premiums. This calculator shows your MAGI with and without the conversion, which tier you land in, and the exact annual premium cost — so you can decide whether the conversion savings outweigh the Medicare cost.

What is the IRMAA Safe conversion strategy?

The IRMAA Safe mode in this calculator caps your annual conversion at the amount that keeps your MAGI strictly below the first IRMAA threshold. This is a conservative strategy that prioritizes protecting Medicare premiums over maximizing tax-bracket conversion headroom. It is particularly useful for retirees already close to an IRMAA tier boundary.

What is the "fill to bracket" strategy?

Rather than converting a fixed dollar amount each year, the fill-to-bracket strategy converts exactly enough to bring your taxable income to the top of a chosen tax bracket — say the 12% or 22% bracket. This maximizes the amount converted at lower rates without accidentally crossing into a higher bracket and triggering a larger tax bill or IRMAA surcharge.

Are there limits on Roth conversions?

No — unlike Roth contributions, Roth conversions have no annual dollar limit. You can convert any amount from a traditional IRA or 401(k) to Roth in any year. However, each dollar converted is added to your ordinary income for that year, so large conversions can trigger higher brackets, the Medicare IRMAA surcharge, or push more Social Security into taxable territory.

Do Roth conversions affect Social Security taxation?

Yes. Roth conversions increase your "provisional income" (MAGI + 50% of SS benefits), which determines how much of your Social Security benefit is taxable. A large conversion can tip you over the thresholds where 50% or 85% of your benefit becomes taxable. This optimizer does not model SS taxation — factor this in when choosing a target bracket.

Can a Roth conversion trigger the Net Investment Income Tax (NIIT)?

Indirectly, yes. The 3.8% NIIT applies to net investment income (interest, dividends, capital gains) once MAGI exceeds $200,000 (single) or $250,000 (MFJ) — thresholds that are not inflation-adjusted. The converted amount itself is ordinary income, not investment income, so it is never directly subject to NIIT. But a large conversion raises MAGI, which can pull existing investment income above the threshold and expose it to the surcharge for that year. This optimizer does not model NIIT — check your MAGI against these thresholds separately, especially if you hold a taxable brokerage account.