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A 65-year-old who just retired with $1.4 million in a traditional 401(k) and no plans to touch it until age 73 has a problem most pre-retirees miss. The eight years between retiring and the first required minimum distribution<\/a> are the cheapest tax years of the rest of their life. Once RMDs start, the IRS, Medicare, and Social Security all begin pulling at the same dollar.<\/p>\n The fix is unglamorous: a partial Roth conversion strategy<\/a> executed in the 60s, sized to fill up the lower tax brackets without spilling into IRMAA<\/a> territory. Done right, it can shave six figures off the lifetime tax bill for portfolios in the $1 million to $2.5 million range.<\/p>\n The RMD Math That Triggers Everything<\/p>\n The first required distribution at age 73 uses a divisor of roughly 26.5 from the IRS Uniform Lifetime Table. On a $1.4 million traditional 401(k), that is about $52,800 in forced ordinary income in year one, before a single Social Security or pension dollar hits the return.<\/p>\n Layer on Social Security. The provisional income formula makes up to 85% of benefits taxable once combined income clears roughly $44,000 for a married couple. A $52,800 RMD plus $50,000 in joint Social Security clears that line easily, and the newly taxable benefits stack on top of the RMD to push the household deeper into the 22% or 24% bracket.<\/p>\n Then comes IRMAA. Medicare Part B and Part D surcharges run on a two-year lookback, and a couple whose modified adjusted gross income clears the first tier (around $212,000 for joint filers in recent guidance) pays an added premium per spouse, per month. Cross a higher tier and the surcharge can run $300 to $400+ per person monthly. A reader who casually executes a $200,000 Roth conversion at 71 may not realize they just bought an IRMAA bill that lands at 73.<\/p>\n Why Your 60s Are the Window<\/p>\n The 2026 brackets give a retired couple breathing room a 73-year-old never sees again. The 22% bracket runs to $211,400 for married couples filing jointly, and the standard deduction is $32,200. A couple with no earned income and Social Security delayed to 70 can convert roughly $130,000 a year from traditional to Roth and stay entirely inside the 22% bracket.<\/p>\n Over six years, that is around $780,000 lifted out of the future RMD base. By age 73, the remaining traditional balance produces a much smaller forced distribution, the Roth balance grows tax-free with no RMD during the owner\u2019s lifetime, and the IRMAA dial stays down.<\/p>\n The macro backdrop favors acting now. The 10-year Treasury sits near 4.6% and the Fed funds upper bound is near 3.8%, both signaling that the current bracket structure under the One Big Beautiful Bill is the law for the foreseeable future. Paying 22% today on a known conversion amount beats paying an effective 32% to 40% later on stacked RMDs, taxable Social Security, and IRMAA premiums.<\/p>\n