Roth Conversion Calculator: Find Your Optimal Conversion Amount

David, 58, had accumulated $750,000 in his Traditional IRA by the time he took early retirement. His financial advisor mentioned Roth conversions, and David liked the idea of tax-free withdrawals later. So he did what seemed logical — he converted $200,000 in a single year.

The tax bill: $52,000.

David paid 26% effective federal tax on that conversion, plus California state taxes. What he didn't realize until later was that his taxable income before the conversion was only $35,000. He had massive room in the 12% bracket — room he completely wasted by converting too much at once.

If David had converted just $59,000 that year (filling the 12% bracket), he'd have paid about $7,100 in federal taxes on the conversion. He could have done similar conversions for the next three years, moving $236,000 to Roth at an average rate of 12% instead of 26%.

The difference? Roughly $26,000 in unnecessary taxes.

This is why Roth conversion math matters. It's not about whether to convert — it's about how much, and when.

The fundamental question

A Roth conversion moves money from a Traditional IRA (or 401(k)) to a Roth IRA. You pay income taxes on the converted amount now, but all future growth and withdrawals are tax-free.

The basic decision comes down to one question: Will your tax rate on this money be higher now or later?

If your current rate is lower, convert now and lock in the savings. If your future rate will be lower, keep the money in Traditional and pay taxes later. If the rates are the same, converting still offers benefits — no RMDs on Roth accounts, and more flexibility in how you manage income.

The challenge is that "current rate" and "future rate" aren't single numbers. Your rate depends on how much you convert. Convert a small amount and you might stay in the 12% bracket. Convert a large amount and you spill into 22%, 24%, or higher.

How tax brackets work with conversions

Think of tax brackets as buckets that fill up with income. Your first dollars of income go into the 10% bucket. Once that's full, additional income spills into the 12% bucket. Then 22%, and so on.

For married couples filing jointly in 2024, the 10% bucket holds $23,200. The 12% bucket holds another $71,100 (up to $94,300 total). The 22% bucket adds $106,750 more (up to $201,050 total).

When you do a Roth conversion, you're choosing how much income to pour into your buckets that year. The goal is usually to fill lower-rate buckets without overflowing into higher ones.

Let's say your taxable income from Social Security, pensions, and investment income is $50,000. You're married filing jointly. That means you've filled the 10% bucket and part of the 12% bucket. You have $44,300 of room left in the 12% bracket before hitting 22%.

If you convert exactly $44,300, you pay just 12% federal tax on every converted dollar — about $5,316. If you convert $64,300 (20,000 more), that extra $20,000 gets taxed at 22% — $4,400 more in federal taxes on a relatively small additional conversion.

The jump from 12% to 22% is the biggest rate increase in the tax code. Missing it by $1 costs you nearly double the tax rate on every dollar above the threshold.

Finding your conversion sweet spot

The optimal conversion amount depends on your specific situation, but the calculation follows a clear process.

Start by projecting your taxable income for the year without any conversion. Include wages (if still working), Social Security (the taxable portion), pension income, investment income, and any required distributions. Subtract your standard or itemized deductions to get taxable income.

Next, identify which tax bracket that puts you in and how much room remains before the next bracket. This is your "bracket space" — the amount you can convert at your current marginal rate.

Then consider whether filling part of the next bracket makes sense. Sometimes paying 22% now is better than paying 24% or higher later. This depends on your Traditional IRA balance, years until RMDs begin, and your expectations about future tax rates.

Finally, check for hidden costs that might change the math. A large conversion can trigger IRMAA surcharges on Medicare premiums (if you're 63 or older), make more Social Security taxable, or eliminate ACA subsidies (if you're on marketplace insurance). These costs can effectively raise your conversion tax rate significantly.

When conversions make the most sense

Certain life situations create ideal conversion windows — periods when your taxable income is temporarily low, making conversions unusually cheap.

The years between retirement and Social Security are often golden for conversions. If you retire at 60 and delay Social Security until 67 or 70, you might have seven to ten years with minimal taxable income. That's a decade of 10% and 12% bracket space that would otherwise go unused.

A year of job loss or career transition can create a similar opportunity. If your income drops dramatically for any reason, consider whether conversions could fill the gap in your bracket space productively.

Moving from a high-tax state to a low-tax state opens a window for state tax savings on conversions. If you're retiring to Florida or Texas, do your conversions after establishing residency. You'll pay federal taxes but skip the state bite entirely.

The year of a spouse's death offers one final year of Married Filing Jointly brackets. Aggressive conversions that year can lock in wider brackets before the surviving spouse shifts to narrower Single filer brackets permanently.

When conversions don't make sense

Converting in high-income years rarely helps. If you're earning $300,000 and paying 35% marginal rates, converting Traditional IRA money at that rate only makes sense if you genuinely expect rates above 35% in retirement — unlikely for most people.

Converting when you'd lose valuable benefits can backfire. Early retirees on ACA marketplace insurance may find that conversion income eliminates their premium subsidies, adding $10,000 or more to the true cost of conversion. The math changes completely when healthcare subsidies are at stake.

Converting from an inherited Traditional IRA to Roth doesn't work — the tax code simply doesn't allow it. You can convert your own Traditional IRA, but inherited accounts must be withdrawn according to their own rules. Don't let anyone tell you otherwise.

Converting and paying taxes from the converted amount itself defeats much of the purpose. If you convert $50,000 and withhold $11,000 for taxes from the conversion, only $39,000 actually goes into your Roth. If you're under 59½, that $11,000 withholding also triggers a 10% early withdrawal penalty. Always pay conversion taxes from outside funds.

The five-year rule explained

Many people worry about the five-year rule with Roth conversions. Here's what actually matters.

Converted amounts can be withdrawn tax-free at any time — you already paid taxes on them. That's not the issue. The five-year rule only affects whether you pay a 10% early withdrawal penalty if you're under 59½.

If you're 59½ or older, the five-year rule is irrelevant to you. You can withdraw converted amounts immediately with no penalty.

If you're under 59½, each conversion starts its own five-year clock. You must wait five years before withdrawing that specific conversion without penalty. But here's the key: you withdraw conversions in the order they were made. Your oldest conversion comes out first.

This is why early retirees planning to use Roth conversions for income need to start early. If you retire at 55 and want to access converted funds at 60, you need to begin converting immediately so the first conversions have "seasoned" for five years by the time you need them.

Beyond federal taxes: the full picture

A conversion calculator needs to account for more than just federal brackets.

State taxes add 0% to 13% depending on where you live. California charges up to 13.3% on conversion income. Texas charges nothing. This dramatically changes the break-even calculation. A conversion that makes sense for a Texas resident might be a bad deal for someone in California.

Medicare IRMAA thresholds create cliffs in the cost structure. If your conversion pushes MAGI above $206,000 (married filing jointly), you'll pay about $2,000 more per year in Medicare premiums — for both spouses. That surcharge applies two years after the conversion year. Missing this in your calculations can turn a smart conversion into a costly mistake.

Social Security taxation has its own thresholds. Conversion income raises your "combined income," potentially pushing more Social Security benefits into the taxable zone. In the phase-in range, each dollar of conversion can make up to 85 cents of Social Security additionally taxable. Your effective conversion rate can be significantly higher than your marginal bracket suggests.

Running your own numbers

Until our calculator launches, you can work through the analysis manually.

Start with last year's tax return. Find your taxable income on the last line before tax calculation. This shows where you currently sit in the bracket structure.

Project any changes for the current year. Will your income be higher or lower? Are you retiring mid-year? Starting or stopping Social Security? Any of these shift the baseline.

Calculate your bracket space by subtracting projected taxable income from the top of your target bracket. For most people targeting the 12% bracket (married filing jointly), that's $94,300 minus your projected income.

Estimate the tax cost by multiplying your conversion amount by your marginal federal rate plus your state rate. A $40,000 conversion at 12% federal plus 5% state costs $6,800.

Check IRMAA thresholds if you're 63 or older. Add your conversion to your MAGI and see if you cross $206,000 (MFJ) or $103,000 (single). If you're close, consider staying just below.

Run the same calculation for next year. If next year looks similar, spreading conversions across years often beats one large conversion.

What our calculator will do

When our Roth Conversion Calculator launches, it will automate this entire analysis.

You'll enter your current Traditional IRA balance, expected income sources, filing status, and state of residence. The calculator will show your bracket space, optimal conversion amount for each bracket, tax cost at different conversion levels, break-even point (how long until Roth savings exceed conversion cost), and projected impact on IRMAA and Social Security taxation.

For those planning multi-year strategies, it will model different conversion scenarios over time, showing total lifetime taxes under each approach.

The goal isn't just to tell you whether to convert — it's to show you exactly how much to convert each year to minimize your lifetime tax burden.

Sign up to be notified when the calculator launches →

Need personalized Roth conversion analysis now? Connect with a retirement advisor who can model your specific situation and create an optimal multi-year conversion strategy.