Quick ReadWithdrawing from a traditional 401(k) first during retirement's pre-RMD years, rather than last, saves a $2.4 million couple roughly $187,000 in lifetime taxes. Leaving a $1.6 million 401(k) untouched until age 73 lets it grow to $2.9 million, pushing effective marginal rates near 40% once RMDs and Social Security stack. In one worked case (with $500,000 taxable, $1.6 million traditional, and $300,000 Roth) it saves roughly $187,000 in lifetime federal taxes and Medicare surcharges. The first RMD, using the IRS Uniform Lifetime Table divisor of 26.5, lands near $109,000 of forced ordinary income on top of Social Security. That trips the first IRMAA tier and pushes 85% of Social Security into taxable territory.