Roth Conversion Calculator Guide: When to Convert & How Much (2026)

What Is a Roth Conversion?

A Roth conversion is the process of moving money from a traditional IRA, SEP IRA, SIMPLE IRA, or pre-tax 401(k) into a Roth IRA. The converted amount is taxed as ordinary income in the year of conversion — but from that point forward, the money grows completely tax-free, and qualified withdrawals in retirement owe zero federal income tax.

The core tradeoff: you pay taxes now, at a known rate, to avoid taxes later at an unknown rate. Whether that trade makes financial sense depends on your current bracket, your expected retirement bracket, how many years of compounding lie ahead, and your estate planning goals.

According to IRS Statistics of Income data, approximately 22 million Americans hold traditional IRAs, with a combined value exceeding $13 trillion. Fidelity Investments reports that roughly 3.2 million households completed a Roth conversion in 2023, with the median conversion amount around $18,000. Many of those were partial conversions — a deliberate strategy to manage tax liability while still shifting wealth into tax-free accounts.

When Roth Conversion Makes Sense (5 Scenarios)

1. You’re in a Lower Bracket Than You Expect at Retirement

This is the fundamental case. If you’re currently in the 22% bracket but expect to land in 32% or higher in retirement — due to Social Security, pensions, or large required minimum distributions — converting now locks in the lower rate. Vanguard research shows that retirees with over $1 million in traditional IRA assets frequently face marginal rates of 32–37% once RMDs stack on top of Social Security income.

2. You’re in a Low-Income Year

A gap year, sabbatical, job transition, maternity leave, or business loss can temporarily drop your taxable income well below your normal bracket. These windows are prime conversion opportunities. Converting $30,000–$50,000 in a year where your income is otherwise low can be done entirely within the 12% or 22% bracket.

3. Before Required Minimum Distributions Begin at Age 73

The SECURE 2.0 Act pushed the RMD start age to 73 (and 75 for those born in 1960 or later). The years between retirement and age 73 — often called the “Roth conversion window” — can be low-income years before Social Security and RMDs begin. Strategic conversions during this window can dramatically reduce future RMDs and the tax bills that come with them.

4. Your IRA Has Declined in Value

Converting during a market downturn means you pay tax on a smaller balance. If your $100,000 IRA drops to $75,000, you convert and pay tax on $75,000. When markets recover, those gains occur in the Roth account, completely tax-free.

5. Estate Planning and Leaving a Tax-Free Legacy

Roth IRAs have no RMDs during the owner’s lifetime, and inherited Roth IRAs allow beneficiaries to withdraw tax-free over a 10-year window. If leaving tax-efficient wealth to heirs is a priority, converting to Roth is one of the most powerful tools available. The IRS estimates the average inherited IRA is worth about $125,000— and every dollar in a traditional IRA carries a deferred tax liability.

The Tax Cost of Converting: What You Actually Pay

Converted amounts are taxed as ordinary income at your marginal rate. There’s no special capital gains treatment, no exclusion, and no averaging. The tax hits in the year of conversion.

The key insight: you don’t pay your top marginal rate on every dollar. You only pay that rate on the portion that falls into that bracket. Converting $50,000 when you’re already in the 22% bracket doesn’t mean you owe 22% on all $50,000 — it means you owe 22% only on the portion of $50,000 that falls within the 22% bracket, and potentially higher rates if the conversion pushes you into the next bracket.

The standard advice: convert up to the top of your current bracket, but not into the next. This “bracket filling” strategy maximizes the amount converted at the lowest possible rate.

Break-Even Analysis: How Long Until Roth Pays Off?

The break-even point is when the tax-free compounding in the Roth account offsets the tax paid upfront. Here’s a simplified comparison assuming 7% annual growth and taxes paid from outside funds:

Critically: this analysis assumes you pay the conversion tax from outside funds (non-IRA cash). If you withhold taxes from the converted amount itself, you lose the compounding benefit on those withheld dollars and the math shifts against conversion. Always pay conversion taxes from a taxable account if possible.

Roth Conversion Strategies: Full vs Partial vs Ladder

Full Conversion

Converting your entire traditional IRA balance in one year. This rarely makes sense for large balances because it typically pushes you into the highest tax brackets. It can be appropriate for small IRAs (under $25,000), inherited IRAs, or situations where you have large offsetting deductions (business losses, charitable bunching).

Partial Conversion (Bracket Filling)

The most common and typically optimal approach. You calculate how much room remains in your current bracket and convert exactly that amount. For example: if your ordinary income is $60,000 and the 22% bracket tops out at $103,350 for a single filer, you have $43,350 of room. Converting up to that amount keeps every converted dollar in the 22% bracket.

Roth Conversion Ladder

A multi-year strategy where you convert a set amount each year — often used by early retirees pursuing FIRE (Financial Independence / Retire Early). The ladder is built over 5+ years, and each “rung” becomes accessible after its 5-year holding period. This requires careful planning around the 5-year rule (see FAQ below) but can result in a substantial portion of retirement assets becoming tax-free over time.

According to Fidelity’s 2025 Retirement Saving Trends report, households that performed Roth conversions over multiple years had 23% higher Roth IRA balances at retirement than those who converted in a single year, largely due to better bracket management.

The Pro Rata Rule and Backdoor Roth

The Pro Rata Rule

If you have both pre-tax and after-tax (non-deductible) money in your traditional IRAs, the IRS doesn’t let you choose which dollars to convert. Every conversion is treated as a proportional mix of pre-tax and after-tax funds.

Example: You have $90,000 in pre-tax IRA funds and $10,000 in non-deductible (after-tax) contributions — a total of $100,000. If you convert $10,000, the IRS treats it as 90% pre-tax ($9,000 taxable) and 10% after-tax ($1,000 tax-free). You can’t simply convert only the after-tax portion to avoid taxes.

This rule is tracked via IRS Form 8606, which you must file any year you make non-deductible IRA contributions or convert IRA funds.

The Backdoor Roth

High earners above the Roth IRA income limits can’t contribute directly to a Roth IRA. The backdoor Roth works around this:

1. Make a non-deductible (after-tax) contribution to a traditional IRA — up to $7,000 in 2026 ($8,000 if age 50+)
2. Convert that traditional IRA to a Roth IRA shortly after
3. Because the contribution was after-tax, little or no additional tax is owed on conversion

The strategy works cleanly only if you have no other pre-tax IRA balances. If you do, the pro rata rule applies and a portion of your conversion will be taxable. One solution: roll all pre-tax IRA funds into your employer’s 401(k) to clear the IRA slate before executing the backdoor Roth.

The 2026 Roth IRA income phase-out begins at $150,000 (single) and $236,000 (married filing jointly), with full ineligibility at $165,000 and $246,000, respectively.

IRMAA: The Medicare Premium Trap

One of the most overlooked costs of large Roth conversions is the Medicare Income-Related Monthly Adjustment Amount (IRMAA). Your Medicare Part B and Part D premiums are determined by your Modified Adjusted Gross Income from two years prior. A large conversion can trigger premium surcharges that last for a full year.

For a married couple, these surcharges apply per person. A conversion that pushes MAGI just $1 over a threshold can cost an extra $1,776 or more per year in Medicare premiums. When planning conversions in retirement, always model the IRMAA cliff before deciding how much to convert.

Frequently Asked Questions

What is a Roth conversion?

A Roth conversion moves money from a traditional IRA (or other pre-tax retirement account) into a Roth IRA. The converted amount is added to your taxable income for the year and taxed at ordinary income tax rates. In exchange, the money grows tax-free and qualified withdrawals in retirement are completely tax-free. There are no income limits on who can do a Roth conversion — anyone with a traditional IRA can convert, regardless of how much they earn.

When does a Roth conversion make sense?

Roth conversion makes the most sense when your current tax rate is lower than your expected future rate. Prime scenarios include: years with unusually low income (job change, early retirement, business loss), before required minimum distributions begin at age 73, when your traditional IRA has declined in value, or when you have many years of tax-free compounding ahead of you. It generally does notmake sense if you’re currently in a higher bracket than you expect in retirement, or if you’d need to use the IRA funds themselves to pay the tax bill.

What is the 5-year rule for Roth conversions?

Each Roth conversion has its own 5-year holding period. To withdraw converted funds tax-free and penalty-free, the conversion must have occurred at least 5 years ago andyou must be age 59½ or older. The 5-year clock starts January 1 of the tax year you made the conversion — so a conversion done in December 2026 is treated as if it occurred January 1, 2026, and its 5-year period ends January 1, 2031. This is separate from the 5-year rule for Roth IRA contributions, which runs from the date you first opened any Roth IRA.

What is a backdoor Roth IRA?

A backdoor Roth is a two-step strategy for high earners who exceed the Roth IRA income limits ($165,000 single / $246,000 married in 2026). Step one: make a non-deductible contribution to a traditional IRA. Step two: convert it to a Roth IRA immediately (or shortly after). Because the contribution was already after-tax, you owe little or no tax on conversion — unless you have other pre-tax IRA money, in which case the pro rata rule applies and a portion becomes taxable. Congress has debated eliminating the backdoor Roth multiple times; it remains legal as of 2026.

How does a Roth conversion affect Medicare premiums (IRMAA)?

Roth conversions increase your Modified Adjusted Gross Income (MAGI), which determines your Medicare Part B and Part D premiums. If your MAGI exceeds $106,000 (single) or $212,000 (married) in 2026, you pay IRMAA surcharges that can add $74 to $443 per month per person to your Medicare costs. These surcharges are based on income from 2 years prior, so a large conversion in 2026 affects your 2028 Medicare premiums. For retirees on Medicare, staying just below IRMAA thresholds is often worth limiting a conversion by a few thousand dollars.