Convert it in slices. Here is how many.

The facts, in one place.

Six quotable sentences on converting over several years, 2026 tables.

1. A Roth conversion is taxed as ordinary income in the year it is done, so the cheapest way to convert a large balance is in slices, each sized to the room left in a chosen bracket. For 2026 the 22 percent bracket on a joint return runs from $100,800 to $211,400 of taxable income; the 24 percent bracket to $403,550.
2. The window is the years between retirement and required distributions, when other income is lowest; once distributions begin at 73 or 75 they fill the brackets themselves, and once Medicare begins the tiers add a second line.
3. Example: a couple with $600,000 pre-tax and $60,000 of other income, filling the 22 percent bracket each year at a 5 percent return, converts everything in 4 years and pays $111,080 of tax, 17.4% of the amount converted.
4. Left alone at the same return, the same balance would be $977,337 after ten years, all of it pre-tax and all of it eventually taxed, at whatever rates then apply, to whoever withdraws it.
5. Today's brackets are held constant, which is the plan's honest limit: the current rates are law only through the years the Act sets, and every year's slice is re-sized with that year's return in hand.
6. The standard deduction ($32,200 joint, $16,100 single) is part of the room: income up to it is taxed at nothing, so the first slice of a conversion in a low-income year can be free.

Filling each bracket.

Fill a lower bracket and it takes longer at a lower rate; fill a higher one and it is done sooner at a higher rate.

How the ladder works.

A conversion is ordinary income in the year it is made, and the brackets are steps, so the cheapest conversion of a large balance is a series of slices, each filling the current bracket to its top and stopping. The room each year is the bracket's top less taxable other income; the slice is the smaller of the room and what is left; the tax is the ordinary tax on the slice at the rates it lands in. The balance that is not yet converted keeps growing, which is why a ladder at a positive return takes longer than the arithmetic of the first year suggests.

The window is the years between retirement and required distributions, when other income is at its lowest and every bracket has the most room. The planner holds today's brackets and deduction constant for every year, which is its honest limit: the current rates are set by law only through the years the Act covers, and a real plan is re-sized every year with that year's return. It also shows the Medicare tier each conversion year's income sets, because a slice that fits the bracket can still cross a tier.

Methodology.

1. Inputs. The pre-tax balance, other income each year, filing status, the bracket to fill, the years available, and the growth on the balance between conversions.
2. The room. The chosen bracket's top (from the revenue procedure's tables) less taxable other income, which is other income less the standard deduction for the status; never below zero.
3. The slice and its tax. The smaller of the room and the remaining balance; the ordinary tax on taxable other income plus the slice, less the tax on taxable other income alone, so a slice that spans two brackets is taxed at both rates.
4. The years. Each year's remainder grows at the stated rate and the next year repeats, until the balance is gone or the years run out; the untouched balance at the same growth is shown for comparison.
5. Medicare. The tier each conversion year's adjusted gross income sets on this year's CMS table, two years out.
6. Validation. A single filer's room and first-year tax pinned by hand across the 12 and 22 percent brackets, a ladder that finishes in exactly four years at no growth, and a three-year ladder at 5 percent that must leave a remainder. A transcription error fails the build.
7. Not modeled. Future bracket changes and indexing, state tax, capital gains and dividends in the stack, the taxable share of Social Security, the senior deduction's phase-out, the five-year rules on the Roth side, and whether converting is right at all. Educational, not advice.

Sources.

1. 1. Internal Revenue Service, Rev. Proc. 2025-32 — 2026 inflation adjustments (tax rate tables § 4.01, capital gains § 4.03, AMT exemptions § 4.10). Every 2026 bracket boundary and base amount for individuals and for estates and trusts; the 0% and 15% capital-gain thresholds; the AMT exemption amounts. Retrieved September 4, 2026; verified September 4, 2026.
2. 2. Centers for Medicare & Medicaid Services, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet, November 14, 2025). The Part B standard premium and deductible, the Part A inpatient deductible, and every row of the Part B and Part D income-related adjustment tables. Retrieved September 4, 2026; verified September 4, 2026.
3. 3. United States Code (Cornell LII), 42 U.S.C. § 1395r(i) — Income-related increase in Part B premium (and, by cross-reference, Part D). That the income used is modified adjusted gross income from the return two years before the premium year, and the mechanism of the tiers. Retrieved September 4, 2026; verified September 4, 2026.
4. 4. Internal Revenue Service, Rev. Proc. 2025-32 — 2026 inflation adjustments (§ 4.14 standard deduction; § 4.42 gift exclusion). The standard deduction amounts, the additional amounts for age or blindness, the $19,000 gift exclusion, and the $194,000 non-citizen-spouse exclusion. Retrieved September 4, 2026; verified September 4, 2026.

Revision history.

This tool reads the federal and annual records; their histories are below.

September 5, 2026

Added the senior deduction's phase-out rate (6 percent of MAGI over the threshold), which the widow's penalty and QCD tools apply.

September 4, 2026

First release of the annual numbers record and page for 2026, and of the IRMAA tool built on its Medicare section: plan and IRA limits from Notice 2025-67, HSA figures from Rev. Proc. 2025-19, Social Security figures from the Federal Register notice, Medicare premiums and both income-related tables from the CMS fact sheet, the standard deduction and gift exclusion from Rev. Proc. 2025-32, and the senior deduction from the IRS's OBBBA guidance.

September 4, 2026

First release of the federal income-tax record for 2026 and the trust income-tax tool: the estates-and-trusts table, the single and joint tables for comparison, capital-gain thresholds, AMT exemptions, the § 1411 trust threshold rule, and the § 642(b) exemptions, all from Rev. Proc. 2025-32 and the Code.

Canonical address: https://consideratecapital.com/tools/roth-conversion-ladder