The HSA six-month look-back: stop contributing before Medicare reaches back
Sign up for Medicare Part A after 65 and your enrollment is backdated up to six months. The IRS applies its zero-contribution rule to those months too. The fix is one phone call, made in time.
Do you have a health savings account, and are you 65 or older? Then read this before you sign up for Medicare Part A, and before you file for Social Security. If you have already done either one, read it today. The rule is simple, but the trap is six months wide, and the fix only works if you make it in time.
Pat's November surprise
Pat is 66, still working through 2027, and contributed the full amount to a health savings account for the year. In November, planning ahead for retirement at the end of December, Pat signed up for Medicare. Part A was backdated six months, to May 1. The IRS now says Pat's contribution limit for the year was four twelfths of the usual amount: $3,333 instead of $10,000. The extra $6,667 is subject to a 6 percent tax every year until it is removed.
Three rules that collide
Rule one. A health savings account has one condition. You must be covered by a high-deductible health plan and by nothing else that counts as other coverage. Medicare counts as other coverage. IRS Publication 969 puts it in one sentence: beginning with the first month you are enrolled in Medicare, your contribution limit is zero.
Rule two. When you enroll in Part A after 65, the enrollment is backdated up to six months, though never to before the month you turned 65. That is usually helpful. Here it is the trap, because the IRS applies the zero limit to the retroactive months too.
Rule three. Applying for Social Security at 65 or later enrolls you in Part A automatically. You cannot take Social Security and decline Part A. So the day you file for Social Security after 65, you have Medicare, and it started six months ago. Same trap, different door.
Only your own Medicare matters. Your spouse's Medicare does not affect your account, even on a family plan. If you are working past 65 and want to keep contributing, the way to do it is to delay both Part A and Social Security until you are ready to stop. Ask Social Security or your state's free SHIP counselors to confirm your own situation before you rely on that.
The arithmetic
The IRS prorates your yearly limit by the months you were eligible. Pat has family coverage and is over 55, so the 2027 limit is $9,000 plus the $1,000 catch-up allowed from age 55, for $10,000. Pat signed up in November, and Part A reached back to May 1. The eligible months are January through April, four of twelve.
| Full-year limit (family, 55 or older) | $10,000 |
|---|---|
| Eligible months | 4 of 12 |
| Prorated limit (4 ÷ 12 × $10,000) | $3,333 |
| Contributed | $10,000 |
| Excess | $6,667 |
| Tax on the excess, every year it stays | 6 percent, about $400 |
Excess contributions are taxed at 6 percent a year for every year they stay in the account. The fix is the excess contribution removal described at the top. It must be done by the tax filing deadline for that year, extensions included. It takes the excess and its earnings back out; the earnings that come out with it count as income that year. Done in time, the 6 percent never applies.
Your stop date, by situation
You are enrolling in Medicare at 65, on time. Your last safe contribution month is the month before your Medicare starts. Someone covered November 1 contributes through October, prorated to ten twelfths of the limit for the year.
You are working past 65 and will apply for Medicare or Social Security later. Count back six months from the month you will apply for either one, whichever is first. Stop contributing the month before that. If you plan to apply in November, Part A reaches back to May, so April is your last safe month and your limit for that year is four twelfths of the full amount. If you plan to retire in March and sign up in March, Part A reaches back to the previous September. August is your last safe month, your limit for that year is eight twelfths, and next year's limit is zero from January.
You are already receiving Social Security at 65. You are enrolled in Part A the month you turn 65. Stop the month before.
What does not change
The account itself is unaffected. You can keep it, invest it, and spend it tax-free on medical costs for the rest of your life, including Part B, Part D, and Medicare Advantage premiums, though not Medigap premiums. Only the contributions stop. And if your spouse is under 65 and covered by the same family plan, your spouse can open an account in their own name and contribute the family limit, so the household loses nothing.
Sources. IRS Publication 969, Health Savings Accounts; medicare.gov, "How to sign up for Part A and Part B"; IRS Revenue Procedure 2026-24 for the 2027 limits of $4,500 self-only and $9,000 family, plus $1,000 at 55 or older.
Educational, not advice. Clear Table Press is not affiliated with the Social Security Administration or Medicare. Figures carry their year; confirm current amounts at ssa.gov and medicare.gov.