In many retirement systems, age 73 marks the point at which tax-deferred accounts are required to begin withdrawals of long-accumulated assets, according to the Internal Revenue Service. The headline cost of that first required withdrawal is usually the tax bracket shown on the IRS distribution table.The bigger cost is how that withdrawal can ripple through the rest of your retirement income and tax picture.Fidelity’s wealth management team flagged this cascade in updated guidance on the required minimum distributions (RMD) strategy, warning that the fix must begin years before the first required distribution. How an RMD triggers a 3-line tax hitRequired minimum distributions are the annual withdrawals the IRS requires from traditional IRAs and most workplace retirement plans starting at age 73. The withdrawal itself is taxed as ordinary income, which is the line every retiree sees first on their annual federal tax return.Social Security benefits become taxable once a retiree’s provisional income crosses specific thresholds that Congress has never adjusted for inflation. The original tier set dates to 1983, with an 85% taxation tier added a decade later in 1993, leaving more retirees exposed each year.Related: Vanguard drops playbook on retirement incomeProvisional income above $34,000 for single filers or $44,000 for joint filers pushes up to 85% of Social Security benefits into the taxable column. The hit extends to Medicare, where the income-related monthly adjustment amount adds a surcharge to Part B and Part D premiums.The 2026 surcharge starts at $109,000 of modified adjusted gross income for single filers and $218,000 for married couples filing jointly.Higher-income retirees pay between $81.20 and $487.00 in additional monthly Part B premiums above the $202.90 base figure, the Centers for Medicare and Medicaid Services confirmed in its 2026 Medicare Parts A & B Premiums and Deductibles fact sheet.The tax torpedo that turns 1 withdrawal into compound damageAdvisors often call the stacking effect a tax torpedo, a marginal-rate spike triggered when each distributed dollar drags more Social Security into the tax base.Roger A. Young, Vice president and senior financial planner at T. Rowe Price, illustrated this in a Kiplinger analysis using a married couple whose extra $1,000 IRA withdrawal added $407 in federal tax rather than the expected $220. More Fidelity:Fidelity offers a lifeline to millions before Social Security shiftsFidelity flags major 401(k), IRA shift as Americans struggleFidelity cuts to the chase on 401(k) best practicesThe marginal rate on that withdrawal climbed to 40.7%, because the same dollar pulled $850 of Social Security benefits into the taxable column. Ray R. Harris, a Registered Social Security Analyst and founder of Social Security Claiming Experts, warned in Kiplinger’s Adviser Intel column that low tax rates in early retirement disguise a future collision with Social Security.
The “tax torpedo” can sharply increase retirement tax bills, as withdrawals trigger additional taxation of Social Security benefits.EmirMemedovski/Getty Images
Fidelity’s Roth conversion playbook for shrinking future RMDsFidelity’s guidance frames Roth conversions as the most direct route to lowering a future RMD, since they reduce the balance divided by the life expectancy factor.Roth conversions move pre-tax dollars from a traditional IRA into a Roth IRA, where qualified withdrawals are tax-free, and no distributions are ever required.The conversion creates ordinary income in the year it happens, so timing the move into low-income years determines whether the strategy ultimately pays off.Reinvesting RMDs not needed for living expensesFor retirees whose monthly spending is already covered by Social Security and pensions, the mandatory withdrawal becomes idle cash that still owes ordinary income tax.Fidelity’s guidance suggests routing the unneeded distribution to a taxable brokerage account and choosing investments designed to keep ongoing annual tax drag low.Jennifer Curtis, wealth planner at Fidelity Investments, told clients in the firm’s wealth management guidance that retirees who do not need their RMD for monthly expenses generally choose among three structured uses for the money. “There are 3 basic options for your RMDs: Spend it, gift it, or invest it,” Curtis said. “In some cases, my clients might use the money for extra spending, like a vacation or a new car. But more often, they choose a combination, so if someone has, say, a $60,000 RMD, they might take a vacation, gift some, and save or invest the rest.”Municipal bonds, broad stock index funds, and low-turnover exchange-traded funds tend to generate less annual tax leakage than dividend-heavy or actively managed bond portfolios.The transfer still creates a taxable event based on the fair market value of the assets on the day they are removed from the IRA.The planning window narrows once mandatory distributions beginOnce mandatory distributions begin, the same dollar can move three lines at once: ordinary income, Medicare premium, and the taxable share of Social Security benefits.A qualified longevity annuity contract is another option Fidelity flagged, allowing retirees to move up to $210,000 in IRA assets into a deferred income annuity.The contract removes that balance entirely from future required minimum distribution calculations, and rules require payments to start by age 85, not at age 85. The holder can elect earlier.Modeling income two or three years ahead gives retirees room to shift dollars from high-tax years to lower-tax ones, Fidelity’s wealth management noted.Related: Fidelity delivers sobering reality check on your money