Can You Start an HSA at Any Time? Eligibility, Proration, Medicare

Yes — you can start an HSA at any time of year. Health Savings Accounts don’t follow an annual enrollment window like most health insurance sign-ups. As long as you meet the eligibility rules on the first day of a given month, you can open and fund one that month. What changes with timing isn’t your ability to open the account; it’s how much you’re allowed to contribute for the year.

What You Need to Be Eligible on the Day You Open It

The foundation is enrollment in a High Deductible Health Plan. For 2026, that means a plan with an annual deductible of at least $1,700 for self-only coverage or $3,400 for family coverage, with out-of-pocket costs (excluding premiums) capped at $8,500 self-only or $17,000 family.¹ Beyond the HDHP itself, three conditions apply:²

You can’t have other health coverage that pays benefits before you meet your HDHP deductible. A limited-purpose FSA covering only dental and vision is fine; a general-purpose FSA usually isn’t.³
You can’t be enrolled in any part of Medicare.
You can’t be claimed as a dependent on someone else’s tax return.

New in 2026: Bronze and Catastrophic Plans Qualify

If you’ve held a bronze or catastrophic marketplace plan and assumed you were shut out of an HSA, that changed on January 1, 2026. Under the One, Big, Beautiful Bill Act, those plans are now treated as HSA-compatible regardless of whether they meet the traditional HDHP thresholds, and they don’t have to be purchased through an exchange to qualify.⁴ The same law made two other changes: paying a monthly fee to a direct primary care physician no longer disqualifies you (and HSA funds can pay those fees), and telehealth services received before you hit your deductible are permanently allowed without breaking eligibility.

How Much You Can Contribute If You Start Mid-Year

The 2026 annual limits are $4,400 for self-only HDHP coverage and $8,750 for family coverage, with an extra $1,000 catch-up for anyone 55 or older.¹⁵ Those totals include everything — your deposits, payroll contributions, and anything your employer puts in.⁶

When you open the account partway through the year, one of two rules governs how much of that limit you actually get.

Monthly Proration

The default is proration. You get one-twelfth of the annual limit for each month you were an eligible individual on the first day of that month.⁷ Enroll in an HDHP on June 1 with self-only coverage and you’d have seven qualifying months, or roughly $2,567 of the $4,400 limit.

The Last-Month Rule

There’s a shortcut for people who become eligible late in the year. If you’re an eligible individual on December 1, the IRS treats you as eligible for the entire year and lets you contribute the full annual amount.⁷

The catch is a 13-month testing period. To keep the extra contributions tax-favored, you have to remain an eligible individual through December 31 of the following year. If you drop your HDHP or pick up disqualifying coverage during that stretch, the amount you contributed above the prorated limit gets added to your taxable income and hit with an additional 10% tax.⁷ The penalty is waived only for death or disability. If your coverage might change, the prorated limit is the safer choice.

You Also Have Until Tax Day for the Prior Year

Contributions for a given tax year can be made up until that year’s tax filing deadline. Contributions for 2025 can be deposited through April 15, 2026.⁷ So if you opened the account late or couldn’t afford to max it out during the calendar year, you have a few extra months to catch up.

How to Actually Open the Account

Once you’ve confirmed your coverage qualifies, you can open an HSA through a bank, credit union, or other financial institution that offers them.⁸ Many employers set one up automatically when you enroll in their HDHP, but you’re not locked in — you can open an HSA anywhere you want.

Setup requires basic identity verification (Social Security number, date of birth, address) under federal banking rules, plus your insurance plan details so the custodian can confirm you have qualifying coverage. You’ll also name a beneficiary.

Funding usually happens by electronic transfer from a bank account or through payroll deduction. Payroll contributions routed through a cafeteria plan count as employer contributions and escape both income tax and payroll taxes.⁹ Money you deposit directly outside of payroll is deductible on your tax return, but you still pay payroll taxes on it. When both options are on the table, payroll deduction is the more tax-efficient one.

Most custodians send a debit card within a couple of weeks so you can pay medical expenses directly from the account. Keep receipts for everything; the IRS can ask you to prove that any distribution went toward a qualified expense.

The Medicare Boundary

The “any time of year” rule has a hard stop. Once you enroll in any part of Medicare, your HSA contribution limit drops to zero. You can keep spending what’s already in the account for qualified expenses, but no new money can go in. If you’re approaching 65 and thinking about opening an HSA, the window closes when Medicare enrollment begins, not on a calendar date the IRS sets.

1
Internal Revenue Service. IRS Notice 2026-05 – Expanded Availability of HSAs Under the OBBBA
2
Office of the Law Revision Counsel. 26 USC 223 – Health Savings Accounts
3
FSAFEDS. Limited Expense Health Care FSA
4
Internal Revenue Service. Treasury, IRS Provide Guidance on New Tax Benefits for HSA Participants Under the One, Big, Beautiful Bill
5
Internal Revenue Service. HSA Limits on Contributions
6
Internal Revenue Service. HSA Contributions
7
Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Health Plans
8
HealthCare.gov. How to Set Up a Health Savings Account
9
Internal Revenue Service. Instructions for Form 8889 (2025)