Best Age for Roth Conversions: The Gap Years 60-72

Margaret is 65, single, and just retired in Denver. Her wages stopped this year, she has $1.2 million in a traditional IRA, and she is not yet claiming Social Security or taking RMDs. Her only income for the next few years is about $18,000 from a small pension and some interest. That puts her taxable income near the bottom of the 12% bracket — and it is the single most valuable tax window of her life. She has 8 years until RMDs begin at 73, and if she does nothing, her first RMD on that IRA will be roughly $45,000, stacking on top of Social Security and pushing her into the 22%–24% range for the rest of her life. The decision in front of her is not whether to convert. It is which years to do it in.

The timeline that defines the answer

“Best age” only makes sense against a timeline, because the right age is defined by what is not happening yet. Every retiree moves through the same three phases, and the conversion sweet spot sits in the middle one:

1. Wages stop (early or standard retirement, ~60–67). Earned income disappears. Your taxable income often drops by 60–90% overnight. This is the start of the gap.
2. The low-income gap years (~60–72). No wages, possibly no Social Security yet, and no RMDs. Your brackets are emptiest here. This is where conversions are cheapest.
3. RMDs force income (73 or 75). Born 1951–1959, your first RMD is at 73; born 1960 or later, it is 75 (SECURE 2.0 Act §107). At 73 the Uniform Lifetime divisor is 26.5, so you must withdraw about 3.77% of the prior year-end balance whether you need the cash or not.

The conversion math is simply this: dollars you convert in phase 2 fill the cheap brackets that are sitting empty. Dollars you leave in the traditional IRA come out in phase 3 on top of Social Security and the RMD itself — in higher brackets, forever. The whole game is moving income from phase 3 back into phase 2.

The two sweet spots inside the gap

The gap is not uniformly equal. Two sub-windows are especially valuable, and they are driven by two different forces — Medicare premiums and required distributions.

Sweet spot one: ~60–62 (beat the IRMAA lookback)

Medicare’s income-related monthly adjustment amount (IRMAA) raises your Part B and Part D premiums when your modified adjusted gross income is high — but it uses a two-year lookback. Your premium at 65 is set by your MAGI at 63. That means a large conversion at 60, 61, or 62 happens before the lookback window that determines your first Medicare premium ever opens. You can convert aggressively in those years without inflating the MAGI that sets your age-65 Part B premium, which starts at a $185.00/mo base in 2026 and climbs through the IRMAA tiers above $103,000 (single) / $206,000 (MFJ) MAGI.

If you retire before 63, these are your “free” years — large conversions here cost income tax only, with zero Medicare-premium spillover.

Sweet spot two: ~66–72 (after the lookback, before RMDs)

From 63 onward, every conversion does feed the IRMAA lookback for a future premium year, so you trade a known tax saving against a possible premium bump. But from about 66 through 72 you are still RMD-free, your brackets are still emptier than they will ever be again, and you can size conversions to fill a bracket while staying under an IRMAA tier threshold. This is the workhorse window: convert up to a target ceiling each year, watch the IRMAA tier line, and keep shrinking the balance before the 26.5 divisor takes over.

Why delaying Social Security widens the window

Your full retirement age is 67 (born 1960 or later), and every year you delay claiming past it earns 8% in delayed retirement credits, up to age 70. That is a powerful pension boost on its own — but it has a second, underappreciated effect: while Social Security is not flowing, it is not in your MAGI, which leaves the cheap brackets wide open for conversions.

Picture two retirees, both 67. One claims Social Security at 67 and starts adding $36,000 of benefits (up to 85% taxable) to their return. The other delays to 70 and has $0 of Social Security for three more years. The second retiree has roughly $30,000 more bracket room each year to convert at a low rate — and a bigger check waiting at 70. Delaying Social Security from 67 to 70 effectively buys you three extra high-room bridge years. That is why the strongest plans pair delay Social Security with convert aggressively in the meantime.

Scenario walk-through: Margaret’s 8-year runway

Back to Margaret — 65, single, Denver, $1.2M traditional IRA, $18,000 pension, planning to claim Social Security at 70. Colorado taxes retirement income at a flat 4.4%, but it offers a generous retirement-income subtraction for those 65+, so we focus on the federal decision. She has 8 years to RMDs at 73.

If she converts nothing, her IRA grows at, say, 5% to roughly $1.77M by 73, and her first RMD is about $67,000 (1,770,000 ÷ 26.5) — landing on top of her Social Security and pension in the 22%–24% bracket, and likely tripping an IRMAA tier. Instead, she fills the 22% bracket each gap year. For 2026 the single 22% bracket runs $48,476–$103,350, so after her standard deduction ($15,750) and pension she can convert roughly $100,000 a year and stay at or below 22%.

By converting roughly $100,000 a year in the 22% bracket, Margaret pays a known, low rate now in exchange for cutting her first RMD from about $67,000 to about $26,000 — and every dollar of her remaining Roth balance grows and comes out tax-free, with no lifetime RMDs on a Roth IRA at all (IRC §408A(c)(5)). The tranche approach — convert a slice each year rather than one giant conversion — is what keeps each dollar in a cheap bracket instead of spiking her into the 32% bracket and a high IRMAA tier in a single year.

The decision rule

Strip away the scenarios and the rule is short:

• Start as soon as your income drops below your target bracket ceiling. For most retirees that is the year wages stop. Do not wait for “the perfect year” — the gap is finite and closes at 73 or 75.
• Prioritize years before Social Security and before RMDs. Those have the most empty bracket room. Pair conversions with delaying Social Security to 70 to maximize the room.
• Front-load ages 60–62 if you retire early, to beat the IRMAA two-year lookback that sets your age-65 Medicare premium.
• Stop converting in any year once your marginal rate would exceed your expected RMD-era rate. If converting the next dollar costs 32% but your RMD years will only ever reach 24%, that dollar should stay in the traditional IRA.

The ceiling is personal: it is the bracket you expect to be in once Social Security and RMDs are both running. Convert up to that rate, not past it.

What most people miss

Three traps quietly shrink the gap-year payoff:

• They wait until 65 to start, then panic-convert. The biggest, cheapest room is often at 60–62, before IRMAA’s lookback and before Medicare even begins. Retiring at 60 and ignoring conversions until 65 wastes the three highest-value years of the entire window.
• They forget the IRMAA cliffs are not phase-ins. IRMAA is a series of cliffs: one dollar of MAGI over a tier threshold (for 2026, $103,000 single / $206,000 MFJ at the first step) bumps the entire Part B premium up a tier — from $185 to $259/mo and beyond. A conversion that crosses a tier by $500 can cost over $1,500 in extra annual premiums. Size each conversion to land just under the line.
• They convert too little because the tax bill stings. The tax on a conversion feels like a loss, but it is a prepayment at today’s known low rate against tomorrow’s forced high rate. Under-converting leaves a large balance to compound into a six-figure RMD that drags Social Security taxation and IRMAA up with it for the rest of your life. The Roth 5-year clock also starts per conversion, so beginning early matters for access flexibility too.

One more: there is no recharacterization. TCJA eliminated the ability to undo a conversion, so once you convert in a tax year, it is final. That is an argument for the tranche approach — convert to a target, confirm the bracket math near year-end, and only then commit, since the deadline is December 31 of the tax year, not April 15.

The lever

The single lever that decides your outcome is where you set your annual conversion ceiling, and how early you start filling it. Set the ceiling at the top of the bracket you expect to occupy once RMDs and Social Security are both flowing — for many retirees that is the 22% or 24% line — then convert up to that ceiling every gap year from the moment wages stop, front-loading 60–62 to beat the IRMAA lookback and slotting the workhorse conversions into 66–72 before RMDs. Start late, convert timidly, and the 26.5 divisor at 73 sets your tax rate for you. Start early, convert to the ceiling, and you set it yourself.