When do I have to enroll in Medicare Part B?

When does delaying Medicare save you money, and when does it cost you for life? Part B enrollment is one of the few retirement decisions where a single missed deadline follows you permanently. Get the timing wrong and you buy a lifetime penalty plus a gap in coverage.

What Part B is and what it costs

Part B is the slice of Medicare that covers doctors, outpatient care, and most of what happens outside a hospital. For 2026, the standard premium is $202.90 a month, with a $283 annual deductible. Higher earners pay more through IRMAA, the income surcharge tied to your tax return from two years ago.

Your Initial Enrollment Period runs seven months: the three months before the month you turn 65, the month itself, and the three months after. Miss that window without a valid reason and you’re exposed.

The penalty is the part that bites

Here’s what most people don’t see coming. The late-enrollment penalty for Part B is 10% of the premium for every full 12 months you could have had it and didn’t, and you pay it for as long as you have Part B. Wait three years, that’s a 30% surcharge that never goes away. On a premium that rises most years, the penalty compounds right along with it.

This isn’t a one-time slap. It’s a tax on a decision you made at 65, collected every month into your nineties.

When delaying is the right call

There’s one clean exception. If you’re still working at 65 and covered by a current employer’s group health plan, through your job or your spouse’s, you can usually delay Part B without penalty and pick it up later through a Special Enrollment Period. The coverage has to be active employer coverage, not retiree coverage and not COBRA. Those don’t count, and people learn that the hard way.

So the real question at 65 isn’t “do I want Medicare.” It’s “do I have qualifying employer coverage right now.” If yes, you may have a reason to wait. If no, enroll on time. The penalty for guessing wrong is too steep to gamble on.

If you have an HSA

One wrinkle for the affluent saver. Once you enroll in any part of Medicare, you can no longer contribute to a health savings account. If you’re still working, still covered by a high-deductible plan, and want to keep funding your HSA, that’s a genuine reason to delay Part B, but only if your employer coverage qualifies. Coordinate the two on purpose. Stumbling into Medicare enrollment can quietly end your HSA contributions mid-year and trigger a tax penalty if you keep funding it.

The whole game with Part B is the calendar. The coverage is the easy part. The deadline is the one that bites, and it bites for life.