Medicare Surprises to Avoid

The expensive Medicare mistakes aren't in the fine print. They're the timing traps and the income surcharge that bills you for a tax decision you made two years earlier.

Why do careful, financially literate people still get blindsided by Medicare? Because the costly parts aren’t the premiums on the brochure. They’re the timing traps and the surcharge that bills you today for a tax return you filed two years ago.

I’ve watched high-net-worth households treat Medicare as a paperwork errand at 65. Sign up, pick a plan, done. Then the surprises arrive, and most of them were avoidable with a calendar and a little second-order thinking.

The late-enrollment penalty that never goes away

Miss your enrollment window and Medicare doesn’t just make you wait. It taxes you for the rest of your life. The Part B late penalty adds 10% to your premium for every 12 months you were eligible and didn’t sign up, and that surcharge sticks permanently. Part D works the same way with its own clock.

The trap catches people who are still working at 65 with employer coverage, or who assume COBRA counts. COBRA does not count as the kind of coverage that protects you from the penalty. Neither does a retiree health plan in most cases. If you’re past 65 and your coverage isn’t from a current employer with 20 or more workers, you’re probably on the clock without knowing it. I go deeper on the mechanics in the enrollment penalties guide.

IRMAA, the bill from two years ago

Here’s the one that stings the affluent most. Your Medicare premium isn’t flat. Above an income threshold, you pay the Income-Related Monthly Adjustment Amount, IRMAA, a surcharge stacked on top of your base Part B and Part D premiums.

For 2026 the standard Part B premium is $202.90 a month. Cross the first threshold and you’re paying $284.10. At the top tier it’s $689.90 a month, per person. For a couple, the top tier runs over $16,000 a year just for Part B, before Part D surcharges.

The cruel part is the lookback. 2026 IRMAA is based on your 2024 income. A one-time spike two years back, a big Roth conversion, a business sale, a fat capital gain, sets your premium today, long after you could do anything about it. I cover the full bracket structure in the IRMAA brackets guide and how to plan around the lookback in IRMAA and MAGI planning.

The coverage gaps nobody mentions at the desk

Original Medicare doesn’t cap your out-of-pocket spending. There’s no annual maximum, which means one serious illness can run without a ceiling. That’s the entire reason Medigap and Medicare Advantage exist, and choosing between them is its own decision I unpack in Medigap vs. Medicare Advantage.

Three more it won’t cover: routine dental, vision, and hearing. For a retiree who needs implants or hearing aids, that’s a real five-figure bill landing on a plan that says nothing about it. And Medicare almost never travels. Care outside the United States is largely on you, which matters if you split the year abroad.

The window that closes quietly

The surprise that costs the most over time is the one-time Medigap window. When you first enroll in Part B at 65, you get a stretch of months where insurers must sell you any Medigap policy at the standard price, no health questions. Miss it, and in most states they can underwrite you later, price you up, or decline you outright after a diagnosis.

So the person who picks Medicare Advantage at 65 to save money, then tries to switch to Medigap at 75 after a health scare, can find the door has quietly shut. That’s a second-order cost the premium comparison never shows you.

How to not get surprised

The fix is a calendar, not a panic. A few moves before each decision:

Mark your enrollment window the month you turn 65, or the month current employer coverage ends. Don’t assume COBRA or retiree plans protect you.
Model your IRMAA two years out. Before a Roth conversion or a big gain, check which bracket the income pushes you into for the premium year down the road.
Treat the first Medigap window as one-time. Decide with the long game in mind, because the easy switch you’re counting on later may not exist.
Run an annual review. Plans, formularies, and IRMAA brackets move every year. The annual Medicare review checklist keeps it to an hour.

Medicare rewards the person who reads the calendar, not the person who reads the brochure. Almost every surprise here was a date someone missed or an income number they never connected to a premium. Connect them early, and the surprises stop being surprises.