Roth Conversion Strategy: A Pre-Retiree's Guide to the Conversion Window

What a Roth conversion actually does

A Roth conversion moves pre-tax dollars from a Traditional IRA, Rollover IRA, SEP-IRA, or SIMPLE IRA into a Roth IRA. The amount converted is added to your ordinary income for that tax year. From that point forward, the converted dollars grow tax-free, are not subject to Required Minimum Distributions during the original owner's lifetime, and pass to heirs income-tax-free.

The decision is rarely about whether Roth is "better." It is about when paying the tax produces the highest after-tax retirement income across the household's full timeline — including the surviving spouse and, in some plans, the next generation.

Who benefits most (and who shouldn't)

Strong candidates

• Pre-retirees age 60–72 with large Traditional IRA / 401(k) balances and a low-income gap year between work and Social Security.
• Households expecting RMDs to push them into a higher bracket than today.
• Married couples planning for the survivor's eventual filing as Single — where the same income jumps roughly two brackets.
• Heirs-focused legacies subject to the SECURE Act's 10-year payout rule for non-spouse beneficiaries.

Weak candidates

• Households likely to spend all pre-tax dollars themselves at a lower future bracket.
• Donors who plan to satisfy RMDs through Qualified Charitable Distributions (QCDs) — the IRA is already exiting tax-free.
• Anyone who must pay the conversion tax with IRA dollars (see below).

The pre-RMD conversion window

Under current law, RMDs begin at age 73 (rising to 75 for those born in 1960 or later, per SECURE 2.0). The years between retirement and the first RMD are usually the lowest-income window of an investor's adult life. That window — often ages 62–72 — is where most of the leverage in Roth conversion planning lives.

Filling brackets without overshooting

The mechanical version of the question is: how much can you convert before the next dollar crosses into a meaningfully higher marginal cost? The marginal cost is not just the federal bracket — it is the bracket plus state income tax plus IRMAA plus NIIT plus the loss of any income-tested credits or ACA subsidies in that year.

A common implementation is to convert each year up to the top of the 24% bracket while income is still pre-Social Security and pre-RMD, then re-evaluate annually as legislation and balances change.

IRMAA, NIIT, and second-order taxes

Three lurking costs frequently ambush Roth conversions:

• IRMAA — Medicare Part B and Part D surcharges based on Modified Adjusted Gross Income from two years prior. A conversion at age 63 first shows up on Medicare premiums at 65.
• NIIT — the 3.8% Net Investment Income Tax applies above $250,000 MAGI (MFJ). Conversions raise MAGI and can pull more investment income into NIIT.
• Social Security taxation — once provisional income clears the upper thresholds, up to 85% of benefits are taxable, creating effective marginal rates that look nothing like the bracket on the chart.

Where to pay the conversion tax from

Pay the federal and state tax on a conversion from a taxable brokerage account, not from the IRA itself. Withholding from the IRA shrinks the converted amount and, if the owner is under 59½, triggers the 10% early-withdrawal penalty on the withheld portion.

1. Confirm sufficient outside cash before initiating the conversion.
2. Elect 0% federal/state withholding on the conversion itself.
3. Pay quarterly estimates (Form 1040-ES) — or use a Q4 IRA distribution with full withholding under the safe-harbor rules if outside cash is short.

The two five-year rules

• Roth IRA five-year rule (earnings): earnings come out tax-free only after five tax years from the first Roth contribution and after age 59½.
• Conversion five-year rule (10% penalty): each conversion has its own five-year clock for the 10% early-withdrawal penalty on the converted principal if the owner is under 59½.

Common mistakes

• Converting in a high-W-2 year instead of waiting for the gap.
• Converting just past an IRMAA tier — paying a surcharge that erases years of conversion savings.
• Forgetting the pro-rata rule when non-deductible IRA basis exists.
• Modeling the conversion only against the owner's own bracket, ignoring the surviving-spouse and 10-year-heir scenarios.

Decision checklist

1. Project taxable income each year through age 75 with and without conversions.
2. Identify the marginal rate ceiling — federal + state + IRMAA + NIIT.
3. Confirm outside cash to pay the tax.
4. Coordinate with Social Security claiming and any QCD plans.
5. Execute mid-year, then re-true at year-end based on actual income.