The three Medicare deadlines that cost people money

Medicare is full of dates. Most of them do not matter much. Three of them do.

Miss one of these three and the cost is not a scolding letter. It is a penalty that can follow you for the rest of your life. The rules are public and the math is simple. But nobody sits you down and explains them.

The three windows

• The birthday window. A seven month window built around the month you turn 65. This is the front door to Medicare.
• The working window. A special window for people who keep a job and its health plan past 65. You can enroll any time while that coverage lasts, and a short clock starts when it ends.
• The yearly window. October 15 to December 7, every year. This is when you can change your plan for the year ahead.

Here is why the stakes are real. Medicare Part B pays for doctor visits, and for care that does not need an overnight hospital stay. Its standard premium, the monthly bill, is $202.90 in 2026. Sign up two full years late, with no other coverage that counts, and Medicare adds 20 percent. That is about $40.58 more every month.

It is not a one time fee. You pay it every month, for as long as you have Part B. For most people, that means for life. And the penalty grows whenever the premium grows.

One note before the math. This guide is education, not personal advice. Rules have exceptions. Your State Health Insurance Assistance Program, called SHIP, gives free one on one help with your own situation.

The next three lessons walk through each window, one at a time. Each window hides a trap that catches smart, careful people. One trap in lesson two has cost some retirees years of penalties. Here is how all three work, and how to walk past them.