Your 65th Birthday Is Coming. Here Is What Changes, and Which Dates Can Cost You.

What changes at 65, with the deadline and who to call

Ten things shift around your 65th birthday. Some run on their own; others start a clock only you watch. Dollar figures are for 2026.

The rows are rules, not recommendations. Which plan fits you and when to claim depend on your health, your doctors and your budget.

Do this first: the birthday box

Every Medicare date counts from one month, so write that month down first.

1. Write the month you turn 65. Born on the 1st? Use the month before. Medicare treats you as reaching 65 a month early.
2. Count back three months. Your sign-up window opens there.
3. Count forward three months. The window shuts there, seven months total. Medicare calls it your Initial Enrollment Period.
4. If you have an HSA, write the month you plan to apply. Count back six months: Part A can start there, but never before your birthday month. The month before that is your last safe month to contribute for.

Say you turn 65 in July and were born on the 14th. Your window runs April through October. Born on July 1 instead? It runs March through September.

A year before: which kind of 65 are you?

The first split is whether Social Security payments already reach your bank. Did they begin 4 or more months before your 65th birthday? Then Medicare enrolls you in Parts A and B automatically. If not, the sign-up is yours to do.

Want to delay Part B once the card shows up? Refuse it in writing. Social Security must receive that refusal before the card’s start date.

The second split is where your insurance comes from. At an employer with 20 or more workers, the job plan pays first. Under 20, Medicare pays first. COBRA and retiree plans don’t count as coverage from a current job, so they do not let you put off Part B safely.

Medicare does not end a Marketplace plan; you must cancel it. And the premium tax credit stops once you can get premium-free Part A, whether or not you sign up. The month depends on your case: usually the month you turn 65 if enrolled automatically, the first full month of coverage if you sign up yourself, and the month after your 7-month window if you never sign up. Credits paid for months you also had Part A may have to be repaid at tax time.

Ten months before: the record that makes Part A free

Part A is free if you or a spouse earned 40 work credits. In 2026, one credit takes $1,890 of earnings, and you can earn up to four a year.

About 99 percent of people with Medicare pay no Part A premium (CMS, 2026).

Without enough credits, Part A costs $311 a month in 2026 with 30 to 39 credits, or $565 with fewer than 30. In your my Social Security account, look for a zero in any year you know you worked.

Fixing a mistake has a time limit: 3 years, 3 months and 15 days after the end of the year you earned the money. After that, only listed exceptions apply, such as an employer that never reported your wages.

Seven months before you apply: the HSA has to stop

IRS Publication 969 puts it in one line: once Medicare enrollment begins, your HSA contribution limit drops to zero, starting that first month. Part A alone is enough to trigger it.

The catch is backdating. If you apply at 65 or later and qualify for free Part A, it can start up to 6 months before the day you apply. Contributions for those months become excess, and the IRS generally charges a 6 percent excise tax on them.

Applying for Social Security at 65 or later also brings Part A. So does your employer’s payroll deposit, if nobody tells the benefits office to stop it. The 2026 HSA limits: $4,400 with self-only coverage, $8,750 with family coverage, and a $1,000 catch-up from age 55.

Three months before to three months after: the window itself

Sign up before your birthday month and Part B starts the month you turn 65. Sign up in your birthday month or the three months after, and it starts the next month. Coverage always begins on the first.

Before 2023, a late sign-up could mean a two- or three-month wait. You can sign up with Social Security by appointment or online at SSA.gov/medicare/sign-up.

The standard Part B premium in 2026 is $202.90 a month (CMS, 2026 Medicare Parts A & B Premiums and Deductibles).

Miss the window without a job-based reason, and the next chance is January 1 to March 31. The Part B penalty adds 10 percent for each full 12-month period you went without it. Two full periods would add $40.58 a month at the 2026 premium, and it lasts as long as you keep Part B.

Drug coverage runs on the same window. After it closes, 63 days in a row without Part D or creditable coverage starts a separate penalty. In 2026 that is 1 percent of $38.99 for each uncovered month, so twenty months adds $7.80 a month.

The month Part B starts: six months that never come back

With Original Medicare, your Medigap open enrollment begins in the first month you are both 65 or older and covered by Part B. It lasts 6 months, happens once and does not repeat.

During those 6 months, insurers have to sell you any Medigap policy they sell in your state. They cannot raise the price over your health. Afterward, most people can be asked health questions and quoted a higher price, or refused.

If you became eligible on or after January 1, 2020, you cannot buy Plan C or Plan F. And if a current job let you delay Part B, your Medigap window waits for it too.

Choosing Medicare Advantage instead? In 2026 no plan’s in-network yearly cap can be above $9,250.

65 is Medicare’s age, not Social Security’s

For anyone born after January 1, 1938, full retirement age is later than 65. Turning 65 in 2026 or 2027 means a 1961 or 1962 birth year, so yours is 67.

Starting at 65 with a full retirement age of 67 is 24 months early. Under Social Security’s formula, 5/9 of 1 percent a month, that is about 13.3 percent less, for life. Waiting past 67 adds 8 percent a year, and the credits stop at 70.

Claiming before full retirement age while you still work brings the earnings test. In 2026, Social Security holds back $1 for every $2 earned above $24,480. The money held back is not lost; your benefit rises at full retirement age to make up for it.

Two money lines that change around 65

For tax years 2025 through 2028, people 65 and older can take a new deduction of up to $6,000 each. It phases out above $75,000 of modified adjusted gross income, or $150,000 on a joint return. It does not change how Social Security benefits are taxed.

The other is Medicare’s income surcharge, IRMAA, priced from your tax return two years back. In 2026 it starts above $109,000 on an individual return or $218,000 joint. If your income fell because you or your spouse stopped working or cut hours, Form SSA-44 asks Social Security to use the newer year.

Fair doubts