Is Medicare a High Deductible Health Plan: HSA Limits and Backdating

Medicare is not a high deductible health plan. Original Medicare fails the IRS tests for an HDHP on several counts, and enrolling in any part of Medicare — Part A, B, C, or D — ends your ability to contribute to a Health Savings Account starting the first month your Medicare entitlement takes effect.¹ The distinction matters because contributions made after that date become excess contributions subject to a 6 percent excise tax.²

Why Medicare Fails the HDHP Test

A qualifying HDHP has to hit specific IRS numbers and follow a specific structure: a minimum annual deductible, a capped annual out-of-pocket maximum, and no coverage of non-preventive care before the deductible is met.³ Original Medicare meets none of these.

Part A Uses Benefit Periods, Not an Annual Deductible

Medicare Part A does not carry an annual deductible. It uses benefit periods. A benefit period begins the day you are admitted as an inpatient and ends only after you have gone 60 straight days without inpatient care. You owe the Part A deductible — $1,736 in 2026 — every time a new benefit period begins, with no annual cap on how many you can have.⁴ Someone hospitalized twice or three times in a year pays it twice or three times. An HDHP by definition has one annual deductible.

The Part B Deductible Is Too Low

The 2026 Part B deductible is $283.⁴ The IRS minimum deductible for self-only HDHP coverage in 2026 is $1,700.³ After you clear that low Part B threshold, Medicare pays 80 percent of most outpatient costs, which is exactly the kind of first-dollar coverage an HDHP cannot provide for non-preventive care.

There Is No Out-of-Pocket Maximum

Original Medicare places no ceiling on what you can spend out of pocket in a year. Your only protection against unlimited cost-sharing comes from buying a Medigap policy or joining a Medicare Advantage plan.⁵ Every HDHP, by law, has to cap out-of-pocket costs — $8,500 for self-only coverage in 2026.³ That missing cap alone would disqualify Medicare.

What This Means for Your HSA

Federal law lets you contribute to an HSA only if you are covered by an HDHP and have no other disqualifying coverage. Medicare is disqualifying coverage. From the first month your Medicare entitlement begins, your HSA contribution limit is zero, and anything you put in after that is excess.¹

Your Limit in the Year You Enroll Is Pro-Rated

In the calendar year you go on Medicare, your annual HSA contribution limit is divided by 12 and multiplied by the number of months you were HSA-eligible. Eligibility is measured on the first day of each month. If Part A starts July 1, you were eligible for January through June, or six months, and can contribute half the annual limit.⁶ At 2026 self-only figures, that works out to $2,200. The $1,000 catch-up available at age 55 or older pro-rates the same way.

The Six-Month Part A Backdating Trap

If you apply for Social Security after 65, your Medicare Part A coverage is automatically backdated up to six months, though never earlier than the month you turned 65.⁷ Any HSA contributions you made during those retroactive months become excess after the fact. Someone who files for Social Security in December 2026 and gets Part A backdated to July 2026 has six months of contributions to unwind.

Medicare MSA Plans Look Like HDHPs but Do Not Restore HSA Eligibility

Medicare Medical Savings Account (MSA) plans are Part C plans that pair a high-deductible insurance component with a plan-funded savings account.⁸ The structure resembles a private HDHP-plus-HSA arrangement, but the MSA account is not an HSA. You cannot make your own tax-deductible contributions to it, and because MSA enrollment is still Medicare enrollment, it still ends your eligibility to contribute to any HSA you own.¹

Spending Your HSA After Medicare Starts

Medicare enrollment stops new contributions. It does not touch the money already sitting in your HSA. You can keep withdrawing those funds tax-free for qualified medical expenses indefinitely.⁶

Once you are 65 and on Medicare, qualified expenses expand to include most Medicare premiums. You can pay the following tax-free from your HSA:

Part B premiums
Part D prescription drug premiums
Medicare Advantage (Part C) premiums
Part A premiums, in the uncommon case that you owe them for lack of work credits

Medigap premiums are the exception. Supplement policy premiums cannot be paid tax-free from an HSA.⁶

After 65, non-medical withdrawals no longer carry the 20 percent penalty. You still owe ordinary income tax on the amount you pull out, similar to a traditional IRA distribution, but the extra penalty is gone.¹

Keeping HSA Contributions Going Past 65

If you want to keep contributing after 65, you have to delay Medicare, and to delay Medicare you generally have to delay Social Security. Anyone already drawing Social Security retirement benefits at 65 is automatically enrolled in Part A and immediately loses HSA eligibility. You cannot separate the two once benefits begin, short of repaying all Social Security received and withdrawing your application within 12 months.

Employer size matters as well. If your employer has 20 or more employees, the employer plan stays primary past 65 and you can remain on that HDHP without enrolling in Medicare. If the employer has fewer than 20 employees, Medicare becomes primary at 65 and the employer plan drops to secondary, which makes delaying enrollment impractical. For many people still working at 65, the cleanest approach is to postpone both Social Security and Medicare until actual retirement, then enroll in both together and stop HSA contributions on the effective date.

Fixing HSA Contributions You Should Not Have Made

If you contributed during months you were on Medicare — often because of the Part A backdating — you can avoid the 6 percent excise tax by withdrawing the excess amount plus any earnings on it before your tax return’s due date, including extensions.⁶ For 2026 contributions, that means April 15, 2027, or October 15, 2027 with an extension. The withdrawn contribution itself is not taxed as a distribution, but the earnings on it must be reported as income for the year the contributions were made.

Miss that deadline and the 6 percent tax applies for each year the excess sits in the account. Excess contributions are reported on Form 5329, Part VII. There is a further six-month window after the original filing deadline (extensions aside) to withdraw the excess and file an amended return; write “Filed pursuant to section 301.9100-2” at the top of that amended return.⁹

1
Office of the Law Revision Counsel. 26 USC 223 – Health Savings Accounts
2
Office of the Law Revision Counsel. 26 USC 4973 – Tax on Excess Contributions to Certain Tax-Favored Accounts and Annuities
3
Internal Revenue Service. IRS Notice 26-05
4
Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
5
Medicare. Costs
6
Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Health Plans
7
Medicare. When Does Medicare Coverage Start
8
Medicare. Medicare Medical Savings Account (MSA) Plans
9
Internal Revenue Service. Instructions for Form 5329