Medicare premiums are not the same for everyone. The Social Security Administration generally uses your tax return from two years earlier to determine Medicare Part B and Part D premiums. For many people enrolling at age 65, income earned around age 63 is what determines their initial premiums. That two-year lookback turns any large IRA withdrawal, Roth conversion, or capital gain in that single year into a premium decision in addition to a tax decision.
The default Part B premium in 2026 is $202.90 per month for beneficiaries below the first income-related monthly adjustment amount (IRMAA) threshold. Above that threshold, the surcharge is added. According to the Centers for Medicare and Medicaid Services, the income-related monthly adjustment amounts affect roughly 8% of people with Medicare Part B, but the share of near-retirees who briefly cross a bracket during a conversion year is meaningfully higher.
How the IRMAA Brackets Work in 2026
The 2026 Part B brackets, based on modified adjusted gross income (MAGI) from the tax return filed two years earlier, look like this for individual filers and joint filers with full Part B coverage:
- MAGI at or below $109,000 individual / $218,000 joint: $202.90
- Above $109,000 up to $137,000 individual / Above $218,000 up to $274,000 joint: $284.10
- Above $137,000 up to $171,000 individual / Above $274,000 up to $342,000 joint: $405.80
- Above $171,000 up to $205,000 individual / Above $342,000 up to $410,000 joint: $527.50
- Above $205,000 up to $500,000 individual / Above $410,000 up to $750,000 joint: $649.20
- Above $500,000 individual / Above $750,000 joint: $689.90
Part D adds a separate surcharge. Above the first threshold, the Part D IRMAA starts at $14.50 and rises to $91.00 at the top bracket. The surcharge applies regardless of which plan a beneficiary chose and is deducted from Social Security payments or billed separately.
A distribution taken during the tax year in which a person turns 63 shows up on the return filed the following spring. Two years after that return is filed, Medicare reads the MAGI line and assigns a bracket. A one-time IRA withdrawal or Roth conversion at that point can affect both current taxes and future Medicare premiums.
Why Age 63 Is the Pinch Point
The underlying mechanics here are straightforward. A distribution taken during the tax year in which a person turns 63 shows up on the return filed the following spring. Two years after that return is filed, Medicare reads the MAGI line and assigns a bracket. A single $60,000 Roth conversion by an individual filer with a baseline MAGI of $95,000 pushes total MAGI to $155,000, crossing two IRMAA thresholds and increasing the monthly Part B premium from $202.90 to $405.80. A distribution at 62 lands two returns before Medicare enrollment and typically clears the lookback window. A distribution at 63 is the one Medicare will read. A distribution at 64 catches the second year of premiums after enrollment.
The base tax cost of that same withdrawal is already within the marginal tax brackets. For 2026, the 24% rate applies to incomes over $105,700 for single filers ($211,400 for married couples filing jointly), and the standard deduction is $16,100 for single filers and $32,200 for married couples filing jointly. IRMAA sits on top of that as a fixed monthly dollar amount tied to a bracket rather than a percentage, so being $1 into a bracket costs the same as being $20,000 into it.
The Cost Backdrop for Households Near Retirement
Household budgets already carry more healthcare costs as they approach Medicare eligibility. Average annual expenditures per consumer unit reached $78,535 in 2024, up from $72,973 in 2022, per the Bureau of Labor Statistics Consumer Expenditure Survey. The personal savings rate has fallen from 5.2% in the first quarter of 2025 to 3.9% in the first quarter of 2026, according to the Bureau of Economic Analysis. Households heading into the two-year lookback window have less cushion to absorb an unexpected jump in premiums.
Inflation compounds the timing problem. The Consumer Price Index reached 335.123 in May 2026, up from 321.465 a year earlier, and the 2026 Social Security cost-of-living adjustment was set at 2.8%. The COLA raises benefits, but IRMAA thresholds adjust separately and can be crossed by a one-time IRA event unrelated to ordinary income.
For readers modeling the tradeoff between a conversion and its downstream premium effect, a Roth conversion calculator can frame the annual dollar impact side by side.
For a deeper walk-through of IRMAA, the Part D surcharge, and other Medicare cost surprises that surface around the two-year lookback, see Medicare’s Hidden Bills guide.
What the Data Actually Says
The two-year lookback penalizes the calendar year the withdrawal lands in rather than IRA withdrawals as a broader category. A distribution at 62 lands two returns before Medicare enrollment and typically clears the lookback window. A distribution at 63 is the one Medicare will read. A distribution at 64 catches the second year of premiums after enrollment. For households planning a large conversion or a one-time IRA withdrawal between ages 63 and 65, the size of the withdrawal and the bracket it falls into matter more than timing preference alone.
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