The Second Tax Window: What You Do at 63 and 64 Sets Your Medicare Premium at 65

Medicare uses a 2-year lookback, so income earned at ages 63 and 64 directly sets Part B premiums when you turn 65.

IRMAA brackets act as hard cliffs. Being just one dollar over the $109,000 threshold jumps a single filer's monthly premium from $203 to $284.

A couple where both spouses hit the top IRMAA bracket pays nearly $11,700 more per year than those at the standard premium.

Medicare premiums at 65 are set by what showed up on the tax return filed two years earlier, when a retiree was 63. That two-year lookback turns ages 63 and 64 into a quiet second tax window, one where a single Roth conversion, a home sale, or a well-timed bonus can quietly reprice the next two years of health coverage.

The standard Medicare Part B premium for 2026 is $202.90 per month, with an annual Part B deductible of $283. That is the sticker price that roughly 92% of enrollees pay. The other slice, the roughly 8% of Part B beneficiaries whose modified adjusted gross income clears the first threshold, pays the Income-Related Monthly Adjustment Amount, or IRMAA, on top.

The Social Security Administration uses the most recent tax return on file to set the current year's premium. In practice, that means 2024 income determines 2026 premiums, and 2026 income will drive 2028 premiums. Someone turning 65 in 2028 is being measured right now, at 63. Someone turning 65 in 2029 is being measured next year, at 64. The window is short, and the trigger events are the ones that tend to cluster right before retirement.

For a single filer in 2026, Part B premiums scale by MAGI bracket:

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MAGI at or below $109,000: $202.90 per month.

Above $205,000 to under $500,000: $649.20.

Joint filers hit the same surcharges at roughly double the income thresholds, starting above $218,000. The brackets function as hard cliffs. One dollar over a threshold moves the whole premium to the next tier for the full year.