Roth Conversion Bracket Fill-Up Calculator 2026
Calculate the exact dollar amount to convert from a Traditional IRA to a Roth IRA in 2026 to "fill up" your chosen federal tax bracket without spilling into the next one. See marginal vs effective tax on the conversion and the after-tax dollars added to your Roth. Free, private, runs entirely in your browser.
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Other considerations: The 5-year rule for converted Roth dollars still applies (you can't withdraw a conversion penalty-free for 5 years). Watch IRMAA — Medicare Part B/D surcharges if your MAGI crosses the $200k+ tier (single) or $400k+ tier (MFJ). State income tax adds on top.
Source: IRS — Rollovers of Retirement Plan and IRA Distributions + IRC § 408A + IRS Revenue Procedure 2024-40 (annual inflation adjustments). Last updated: May 3, 2026.
What Is a Roth Conversion Bracket Fill-Up?
A Roth conversion bracket fill-up is the strategy of converting just enough money from a Traditional IRA or 401(k) into a Roth IRA to push your taxable income exactly to the top of a chosen federal tax bracket — without spilling into the next, higher bracket. Every dollar you convert is taxed as ordinary income at your marginal rate that year, so converting beyond the bracket ceiling means each additional dollar gets taxed at the next higher rate. Filling up the 12% bracket at $96,950 of taxable income (MFJ 2026) is the most common target because the next jump is to 22% — a significant marginal step. Source: IRS — Rollovers of Retirement Plan and IRA Distributions.
This calculator applies the 2026 federal income tax brackets (post-OBBB, inflation-indexed estimate from IRS Revenue Procedure 2024-40 carried forward) to your filing status, computes how much room remains in your chosen bracket given your current taxable income, and tells you the exact conversion amount that fills it without going over. It also shows the federal tax owed on that conversion, the effective tax rate, and the after-tax dollars that arrive in your Roth — money that grows tax-free for life under IRC § 408A.
2026 Federal Tax Brackets (MFJ & Single)
For 2026, the projected federal ordinary income tax brackets (using the 2025 amounts indexed for inflation under the One Big Beautiful Bill Act, P.L. 119-21, which made the post-2017 Tax Cuts and Jobs Act rates permanent) are:
- Married Filing Jointly: 10% to $23,850 · 12% to $96,950 · 22% to $206,700 · 24% to $394,600 · 32% to $501,050 · 35% to $751,600 · 37% above.
- Single / MFS: 10% to $11,925 · 12% to $48,475 · 22% to $103,350 · 24% to $197,300 · 32% to $250,525 · 35% to $626,350 · 37% above.
- Head of Household: Bracket ceilings sit between Single and MFJ — used by this calculator.
The most common fill-up targets are the 12% bracket (small marginal step from low-income years) and the 24% bracket (the cliff before the 32% bracket — a large step, so filling exactly is most valuable here). The IRS Revenue Procedure 2025-XX will set the final 2026 figures officially in late 2025; this calculator updates whenever the official numbers are published.
Why Bracket Fill-Up Beats Lump-Sum Conversion
Converting an entire $500,000 Traditional IRA in one tax year forces most of that conversion into the 32% or 35% federal bracket plus state tax — often 40%+ in California or New York. Bracket fill-up, executed annually over many years (often during a "Roth window" between retirement and Required Minimum Distributions at age 73), keeps every converted dollar at 12% or 24% rates. Over a 10-15 year window, this strategy can save $50,000–$200,000 in lifetime federal tax versus a lump-sum approach.
Time the conversion before December 31 of each year, since IRC § 408A treats Roth conversions as completed in the calendar year the funds leave the Traditional IRA. Pair with a market drawdown if possible — converting depressed asset values means more shares cross the bracket ceiling per tax dollar, and the recovery happens inside the tax-free Roth wrapper.
Key Risks and Limits to Watch
Three risks deserve specific attention. First, the 5-year rule: each conversion has its own 5-year clock for penalty-free withdrawal of the converted principal — pre-59½ retirees executing back-to-back conversions need to track each year separately. Second, IRMAA: if a conversion pushes MAGI over $206,000 single or $412,000 MFJ (2026 estimates), Medicare Part B and Part D premiums jump 1.4–3.4× for the next two calendar years, sometimes erasing the tax savings. Third, NIIT: although the conversion itself is not net investment income, it raises MAGI and can push other investment income into the 3.8% NIIT zone above $200,000 single / $250,000 MFJ.
Also consider state income tax (this calculator handles federal only — add 5–13% in states like CA, NY, OR, MN), Social Security taxability tipping points if you're already collecting, and ACA premium tax credits if you're under 65 and on a marketplace plan. Last updated: May 3, 2026.