Medicare open enrollment 2027: the numbers that changed

Medicare’s annual open enrollment period opens on October 15, 2026 and closes on December 7, 2026. Whatever you pick in that window becomes your coverage on January 1, 2027, and for most people it stays put for the whole year.

Most of the 2027 numbers are already public. CMS released its 2027 Medicare Advantage and Part D landscape on September 28, and the Part D benefit parameters were set in April. One big piece is still missing, the 2027 Part B premium, which depends on your tax return from two years earlier.

This post covers what’s known, what’s pending, and how the pieces fit into a retirement budget. It explains the rules and does not recommend a plan.

What you can change during open enrollment

Per Medicare.gov, between October 15 and December 7 you can:

• Join, drop or switch to another Medicare Advantage plan (with or without drug coverage)
• Switch from Original Medicare to Medicare Advantage, or back
• Join, drop or switch a stand-alone Medicare drug plan if you’re in Original Medicare

Changes take effect January 1, 2027, provided the plan receives your request by December 7.

There’s a second, narrower window: the Medicare Advantage Open Enrollment Period, January 1 – March 31. It’s only for people already in a Medicare Advantage plan, who can switch to a different Advantage plan or drop back to Original Medicare and add a separate drug plan. Those changes start the first of the month after the plan gets the request.

Part D: a higher cap and a higher deductible

The Inflation Reduction Act redesigned Part D starting in 2025: the old “donut hole” coverage gap is gone, and there’s a hard annual ceiling on what you pay out of pocket for covered drugs. That ceiling is indexed every year by the Part D “annual percentage increase,” which tracks growth in per-person drug spending, not general inflation. CMS’s CY 2027 Final Rule codifies that structure permanently.

Here are the standard-benefit parameters from Table V-2 of CMS’s CY 2027 Rate Announcement:

Two details to know:

• The deductible is a maximum. Plans can set a lower deductible (some set $0), and many do for at least some drug tiers.
• The cap limits your spending on covered drugs. Once you reach $2,400 in out-of-pocket costs, you pay nothing more for covered Part D drugs for the rest of 2027. Premiums don’t count toward the cap, and drugs not on your plan’s formulary aren’t covered at all.

The cap rose 14% ($300), far more than general price inflation. Part D’s parameters follow drug-spending growth, which has been running well ahead of CPI.

For a household modelling retirement healthcare costs, the cap is the number to use. It bounds the worst case for drug costs: premiums × 12, plus at most $2,400 per person for covered drugs.

Premiums: Advantage down, stand-alone drug plans flat or up

CMS’s September 28 release gives the projected averages for 2027:

Behind those averages:

• The Part D Premium Stabilization Demonstration ends after 2026. CMS said in July that plan sponsors now have enough experience with the redesigned benefit to price without it. The demonstration had held down some stand-alone plan premiums in 2025 and 2026, so individual plans that leaned on it may rise more than the average.
• The Part D base beneficiary premium for 2027 is $41.33, per CMS’s July 28 bid-amount release. Growth in that figure is capped at 6% a year from 2024 through 2029 by the Inflation Reduction Act. It’s a reference number used in calculating premiums and late-enrollment penalties, not what any particular plan charges.
• Plan choice is broad. CMS counts 5,532 Medicare Advantage plans for 2027 (5,553 in 2026), with 97% of beneficiaries having access to 10 or more, and 93% of non-low-income beneficiaries able to get an enhanced Part D plan for under $6 a month.

The averages tell you little about your plan. A stand-alone plan can raise its premium, drop a drug from its formulary, or move it to a different tier in a year when the national average barely moves. Every plan sends an Annual Notice of Change in the fall for this reason. The main open-enrollment task is checking your actual drug list against next year’s formularies.

What’s still pending: Part B

The 2027 Part B premium and deductible haven’t been published yet. CMS typically announces them in November. The 2026 figures were released November 14, 2025. For reference, the 2026 numbers are:

Because the Part B premium is deducted directly from most Social Security checks, the November announcement lands alongside the 2027 Social Security COLA. The COLA is the gross raise, and the change in the Part B premium is a big part of what decides the net. We covered how that COLA is calculated in how CPP, OAS and Social Security raises work.

IRMAA: why your 2025 tax return sets your 2027 premiums

Higher-income beneficiaries pay an income-related monthly adjustment amount (IRMAA) on top of the standard Part B and Part D premiums. The timing trips people up: Social Security uses the modified adjusted gross income (MAGI) from your tax return two years before the premium year (falling back to three years if the two-year-old return isn’t available). So:

• 2026 premiums are based on 2024 income
• 2027 premiums will generally be based on 2025 income
• Income you realize in 2026 shows up in 2028 premiums

The 2026 brackets, from CMS:

The 2027 brackets arrive with the Part B announcement in November. IRMAA works in cliffs, not a gradual phase-in: a single dollar over a threshold triggers the full surcharge for that tier, per person, for the year.

The two-year lag is why IRMAA matters for tax planning well before age 65. A Roth conversion, a large capital gain, or the first year of required minimum distributions all raise MAGI, and the premium effect appears two years later. A planner modelling a multi-year conversion ladder typically maps each year’s MAGI against the IRMAA tiers that will apply two years on.

If your income has dropped since the lookback year because of a qualifying “life-changing event” (retirement or reduced work hours, marriage, divorce, the death of a spouse, among others), Social Security lets you ask for a redetermination using Form SSA-44 and more recent income.

How this fits into a retirement plan

Medicare costs are predictable once you’re enrolled and hard to predict before. The rules above lead to a few modelling points:

• Bound the drug-cost risk. With a hard Part D cap, a reasonable worst case for covered drugs is the cap itself ($2,400 per person in 2027), plus premiums.
• Model premiums growing faster than CPI. Part B rose about 9.7% from 2025 to 2026 ($185.00 → $202.90), and the Part D cap rose 14% for 2027. Healthcare inflation assumptions that track general CPI tend to understate this line.
• Treat MAGI as a lever with a two-year delay. Withdrawal order (which account you draw from in which year) changes MAGI and therefore IRMAA two years later. Our withdrawal order guide walks through how account sequencing affects taxable income.
• Retiring before 65 is a different problem. Medicare eligibility generally starts at 65; the bridge years need their own coverage. See health insurance before Medicare.

To see how a healthcare line and premium growth assumption change your retirement timeline, use the US retirement calculator which runs a year-by-year projection, and the Social Security calculator, which shows how your claiming age interacts with the net check after Part B.

Key dates

This post explains how Medicare’s 2027 rules and published figures work. It isn’t advice on which plan to choose; plan details vary by county and by the drugs you take. Medicare.gov’s Plan Finder and your State Health Insurance Assistance Program (SHIP) offer free, plan-specific help.