Chapter 14: Medicare at 65 Does Not Mean Social Security at 65
The worksheets from Chapter 14 of Fifty-Five. Type your own numbers, or try an example from the book to see how each one works.
Your enrollment window
The seven months you can sign up for Medicare around your 65th birthday, and the three months that start your coverage on time.
The formula: Month you turn 65 − 3 months = Window opens. Month you turn 65 + 3 months = Window closes, at the end of that month.
The calculator needs JavaScript. The paper worksheet below does not: it is the same arithmetic, written out.
The paper worksheet
Birth year ______ + 65 = Year you turn 65 ______. Month you turn 65 ______ (move back one month if your birthday is on the 1st)
Window opens: the 1st of ______ (three months earlier)
Window closes: the last day of ______ (three months later)
Months to sign up so coverage starts on time: ______, ______ and ______ (the three before your birthday month)
Walk through it, step by step
- Add 65 to your birth year. That's the year you turn 65.
- Write your birth month. If your birthday is on the 1st, use the month before instead.
- Count back three months, one at a time. If you pass January, go back to December of the year before. That's the month your window opens, on the 1st.
- Count forward three months from your birth month. If you pass December, go to January of the next year. Your window closes on the last day of that month.
- Circle the three months before your birth month. Sign up then, and coverage starts on the first day of your birth month.
- Put a reminder on your calendar for the first of those three months.
Check your answer
- Count every month from the opening month to the closing month, including both. You should get 7.
- Your birth month (or the month before, for a 1st-of-the-month birthday) should be the fourth of the seven.
Figures this worksheet uses, and where they come from: The Initial Enrollment Period: seven months around the month you turn 65, moved one month earlier for a birthday on the 1st (Medicare.gov, When does Medicare coverage start?).
The Part B late penalty
What missing your enrollment window can cost, every month, for as long as you have Part B.
The formula: Full 12-month periods without Part B × 10% × Standard premium = Penalty each month
The calculator needs JavaScript. The paper worksheet below does not: it is the same arithmetic, written out.
The paper worksheet
Months without Part B ______ ÷ 12 = ______ (drop any decimal) = Full periods ______
Full periods ______ × 10% = Penalty rate ______%
Standard premium $__________ × Penalty rate = Penalty each month $__________
Walk through it, step by step
- Count the months from the end of your Initial Enrollment Period until your Part B starts, leaving out any months you had coverage from current work.
- Divide by 12. Drop anything after the decimal point. That's your number of full periods.
- Multiply by 10%. That's your penalty rate.
- Multiply the current standard Part B premium by the penalty rate. That's your monthly penalty. It's figured on each year's standard premium, so it rises when the premium does.
Check your answer
- Your penalty rate must be a multiple of 10%: 0%, 10%, 20% and so on. If it isn't, you didn't drop the decimal.
- The penalty is always a share of the standard premium, never of an IRMAA amount.
- Social Security and Medicare figure the official penalty. Use this to see why the window matters.
Figures this worksheet uses, and where they come from: The Part B late enrollment penalty: 10% of the standard premium for each full 12-month period without Part B (Medicare.gov, Avoid late enrollment penalties); The 2026 standard Part B premium, $202.90 a month (CMS, 2026 Medicare Parts A & B Premiums and Deductibles).