Roth Conversion Tax Calculator: Should You Convert Your IRA?

How a Roth Conversion Works: The Tax Mechanics

A Roth conversion is the act of moving money from a traditional IRA, SEP IRA, SIMPLE IRA, or 401(k) into a Roth IRA. The IRS treats the converted amount as ordinary income in the tax year of the conversion, reported on Form 1040 via Form 8606. You pay tax at your marginal rate, and in return the money enters the Roth permanently — growing tax-free and leaving the account tax-free when you take qualified distributions.

Unlike direct Roth contributions, there is no income ceiling on conversions. A surgeon earning $800,000 a year can still convert $100,000 from a traditional IRA to a Roth in the same year, paying tax at the 37% rate if that is where the income lands. The question is not whether you can convert — it is whether the math makes sense given your current and projected future tax rates.

The conversion is irreversible. Prior to 2018, taxpayers could "recharacterize" — undo a conversion if markets dropped after the conversion date. The Tax Cuts and Jobs Act permanently eliminated that option. Converting and watching the assets fall in value is a real risk, which is why timing conversions to market downturns can be advantageous: you pay tax on a lower value, and the recovery happens inside the tax-free Roth environment.

The 2026 Bracket-Filling Strategy: Step by Step

The core Roth conversion strategy for most taxpayers is bracket-filling: calculate how much room you have until the top of your current tax bracket, then convert exactly that amount. Here are the 2026 ordinary income tax brackets you are filling:

Example calculation: Maria files jointly. Her combined Social Security, pension, and investment income produces $140,000 in taxable income after the $32,200 standard deduction. She is in the 22% bracket. The top of the 22% bracket for MFJ filers is $206,700. That means she has $206,700 − $140,000 = $66,700 of room before hitting the 24% bracket. Converting $66,700 costs her $66,700 × 22% = $14,674 in federal income tax — paid from outside funds if possible to maximize the Roth balance. She moves $66,700 permanently into the tax-free Roth environment.

Crucially, she does not convert $100,000 and spill $33,300 into the 24% bracket unless she has a specific reason to accept the higher rate. The strategy is surgical: fill the bracket, stop at the ceiling. Use our Income Tax Calculator to find your current taxable income before running the conversion math.

When Does a Roth Conversion Make Financial Sense?

The decision reduces to a single question: will you pay a higher tax rate on this money now, or later? If your current rate is lower than your expected future rate, conversion wins. The tricky part is that "future rate" is not just your future marginal bracket — it includes Social Security taxation, RMD-forced income, and the death of a spouse.

According to a 2024 Vanguard analysis of retiree tax trajectories, approximately 60% of retirees with IRA balances above $500,000 would have benefited from Roth conversions during the years immediately before RMDs began — the so-called "golden window" between retirement and age 73. During those years, earned income drops but RMDs have not yet begun, creating a temporary low-income trough ideal for conversions.

Scenarios Where Conversion Is Clearly Favorable

• You are in the 12% bracket now and expect to be in the 22% or higher bracket in retirement due to large RMDs from a growing IRA.
• Your IRA is substantial. Per IRS actuarial tables, a $1 million IRA at age 73 requires an RMD of roughly $36,900 in year one — stacked on top of Social Security and any pension, this easily pushes couples into the 22-24% bracket.
• You have a surviving spouse concern. A married couple may be in the 22% bracket together, but when one spouse dies, the survivor files single at much higher rates. Conversions while both spouses are alive at lower joint rates are a well-established planning strategy.
• You inherited a traditional IRA. Non-spouse beneficiaries must empty the account within 10 years under the SECURE Act. Converting to a Roth during low-income years within that window reduces the tax hit.
• You want to reduce future RMDs. Roth IRAs have no required minimum distributions during the original owner's lifetime. Converting reduces the size of your traditional IRA and therefore reduces future mandatory taxable distributions.

Scenarios Where Conversion Is Questionable

• You are currently in the 37% bracket and expect a lower rate in retirement — deferral wins.
• You would need to liquidate the converted funds to pay the tax bill, shrinking the Roth balance significantly.
• You are in a high-tax state now but plan to retire in a no-income-tax state — conversion today means paying state tax on income you would otherwise avoid entirely.
• You are close to a Medicare IRMAA threshold and a conversion would trigger a $600–$900/month premium surcharge for two years.

IRMAA: The Hidden Conversion Trap for Medicare Recipients

IRMAA — the Income-Related Monthly Adjustment Amount — is an additional Medicare Part B and Part D premium imposed on high-income beneficiaries. The surcharge is based on your Modified Adjusted Gross Income from two years prior. A large Roth conversion in 2026 affects your Medicare premiums in 2028.

For 2026, IRMAA surcharges kick in when MAGI exceeds $106,000 for single filers and $212,000 for married filing jointly (based on 2024 IRMAA thresholds; 2026 thresholds will be slightly higher due to inflation adjustments). The first IRMAA tier adds approximately $594 per year per person in Part B premiums. Crossing an IRMAA cliff with a large conversion can cost a married couple $2,400–$4,800 per year for two years — a real cost that must factor into the conversion math.

The solution is to convert up to — but not across — the IRMAA threshold. If you are single with $90,000 in MAGI and the IRMAA cliff is at $106,000, you can convert up to $16,000 without triggering the surcharge, assuming no other income spikes. Always confirm the current-year IRMAA thresholds before finalizing any conversion decision.

The 5-Year Rule: What You Must Know Before Converting

Roth IRAs are governed by two separate 5-year clocks, and confusing them is one of the most common planning mistakes. The first clock applies to the account itself: you must have had any Roth IRA open for at least 5 years before qualified withdrawals of earnings are tax-free. The second clock applies to each conversion separately.

Under the ordering rules of IRS Publication 590-B, converted amounts are withdrawn before Roth earnings. Each conversion dollar is subject to a 10% early withdrawal penalty if you access it within 5 years of the conversion — unless you are age 59½ or older at the time of withdrawal. This means a 56-year-old who converts $50,000 in 2026 cannot access those specific dollars penalty-free until 2031.

For retirees over 59½, this rule is irrelevant — the 10% penalty no longer applies. But for pre-retirement conversions, particularly those using the "Roth conversion ladder" strategy to fund early retirement withdrawals, the 5-year rule must be tracked separately for every conversion year. Pair your conversion strategy with our complete Roth IRA tax guide to understand both clocks in detail.

2026 Changes: Mandatory Roth Catch-Up Contributions

Beginning January 1, 2026, SECURE 2.0 Act Section 603 takes effect: employees who are age 50 or older and earned more than $145,000 in Social Security wages from the same employer in the prior calendar year must make any 401(k) catch-up contributions as Roth catch-up contributions — not pre-tax. This threshold is indexed for inflation.

In practical terms, if you earned $150,000 in 2025 and want to make the $7,500 age-50+ catch-up contribution to your 401(k) in 2026, it must go into your designated Roth account within the plan. You lose the immediate pre-tax deduction on that $7,500, but it grows and distributes tax-free. The mandatory Roth catch-up effectively forces higher-earning employees into a conversion-like decision each year.

Full Conversion Example: Maria's Optimal 2026 Strategy

Let us finish Maria's full calculation. Here is her 2026 income picture:

Maria has $166,800 of room in her 22% bracket. But she needs to check IRMAA. Her MAGI (before conversion) is approximately $72,100. Adding a $100,000 conversion brings her MAGI to $172,100 — still safely below the $212,000 MFJ IRMAA threshold. She could actually convert up to $139,900 before hitting the 24% bracket ceiling AND stay comfortably below IRMAA.

Decision: Maria converts $100,000 this year and plans to convert additional amounts over the next 4-5 years before RMDs begin at age 73. Her projected 12-year RMD from the $680,000 IRA (assuming 6% annual growth) would be approximately $65,000 per year — stacked on Social Security and the pension, this would put her firmly in the 32% bracket. Each dollar converted now at 22% instead saves 10 cents in future marginal tax. Over $100,000, that is $10,000 in lifetime tax savings on that tranche alone.

Paying the Tax: Inside vs Outside the IRA

One of the most consequential decisions in a Roth conversion is where the tax money comes from. If you convert $60,000 and pay the resulting $13,200 tax bill (at 22%) by withholding from the conversion itself, only $46,800 enters the Roth. If you pay the $13,200 from a taxable brokerage account or savings, the full $60,000 goes into the Roth.

The math strongly favors paying from outside funds. The $13,200 paid from savings is effectively a post-tax contribution to the Roth — it funds the tax shield on $60,000 of future tax-free growth. Paying from the IRA itself reduces the converted balance and defeats much of the long-term benefit. Never withhold federal tax from the conversion if you have outside funds available to cover the bill.

If you convert in the latter part of the year and the conversion is large, consider making a fourth-quarter estimated tax payment to the IRS to avoid underpayment penalties. Use our estimated tax payment guide to calculate the safe harbor amount.

How Roth Conversions Reduce Required Minimum Distributions

Required minimum distributions (RMDs) begin at age 73 (age 75 for those born in 1960 or later, under SECURE 2.0). The RMD amount is calculated by dividing your prior December 31 IRA balance by an IRS life expectancy factor. A $1,500,000 IRA at age 73 requires an RMD of approximately $56,000 using the Uniform Lifetime Table factor of 26.5. By age 78, the same balance (assuming 6% growth) generates an RMD exceeding $80,000.

Converting $100,000 per year for 5 years before age 73 reduces the IRA by $500,000 — cutting the first-year RMD by roughly $18,900. That reduction is permanent and compounds: every future RMD is smaller because the denominator (the IRA balance) is smaller. For married couples, reducing RMDs also reduces the Social Security taxation cliff, potentially keeping a larger share of benefits tax-free.

Roth IRAs are exempt from RMDs during the original owner's lifetime. That exemption means your heirs inherit a larger, unconstrained account — a significant estate planning benefit. See our RMD Calculator guide to model the RMD impact of different conversion amounts on your specific balance.

Roth Conversion vs Backdoor Roth: What Is the Difference?

These are often confused but they serve different purposes. A Roth conversion moves existing pre-tax IRA money into a Roth — it applies to any taxpayer at any income level. A backdoor Roth is a workaround for high earners who cannot contribute directly to a Roth IRA due to the income phase-out ($153,000–$168,000 for single filers; $242,000–$252,000 for married in 2026). The backdoor strategy involves making a nondeductible traditional IRA contribution and then immediately converting it.

The pro-rata rule complicates backdoor conversions if you have other traditional IRA balances. If you have $90,000 in a pre-tax IRA and make a $7,000 nondeductible contribution, the IRS taxes your conversion proportionally: only 7.2% ($7,000 ÷ $97,000) of the conversion is tax-free. Our Backdoor Roth IRA guide explains the pro-rata rule with worked calculations.

Frequently Asked Questions

Related Guides