An HSA contribution calculator works out how much you can put into a health savings account when you had qualifying HDHP coverage for only part of 2026. Formula: Limit = annual limit × eligible months ÷ 12, plus $1,000 × eligible months ÷ 12 if age 55+; with the last-month rule, use the full annual amounts. With self-only coverage for six months, the 2026 limit is $4,400 × 6 ÷ 12 = $2,200. If you are 55 or older, the $1,000 catch-up is prorated the same way, adding $500.
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How to use the HSA contribution calculator
- Enter the IRS annual limit for your coverage: $4,400 for self-only or $8,750 for family coverage in 2026.
- Enter the number of months you were an eligible individual on the first day of the month.
- Choose whether you were eligible on December 1 and want to use the last-month rule.
- Choose whether you are age 55 or older at the end of the year.
The HSA contribution calculator then shows the base limit, the catch-up and the total.
What formula does the HSA contribution calculator use?
- Base limit = annual limit × eligible months ÷ 12.
- Catch-up = $1,000 × eligible months ÷ 12, for people age 55 or older, as in the Form 8889 worksheet.
- With the last-month rule, both are the full annual amounts.
A month counts only if you were eligible on the first day of that month. Employer contributions, including cafeteria plan pay-ins, count toward the same limit.
HSA contribution calculator worked example
Results from the HSA contribution calculator for 2026:
| Situation | Base limit | Catch-up | Total |
|---|---|---|---|
| Self-only, 6 months, under 55 | $2,200.00 | $0 | $2,200.00 |
| Self-only, 6 months, age 55+ | $2,200.00 | $500.00 | $2,700.00 |
| Family, 4 months, under 55 | $2,916.67 | $0 | $2,916.67 |
| Family, 9 months, age 55+ | $6,562.50 | $750.00 | $7,312.50 |
| Self-only, last-month rule, age 55+ | $4,400.00 | $1,000.00 | $5,400.00 |
The last-month rule doubles the six-month figure here, but it comes with a testing period, explained below.
The last-month rule and the testing period
IRS Publication 969 says that if you are an eligible individual on the first day of the last month of your tax year, December 1 for most people, you are treated as eligible for the whole year. That lets someone who starts HDHP coverage mid-year contribute the full amount.
The catch is the testing period. You must stay eligible from December 1 through December 31 of the following year. If you lose eligibility in that time for a reason other than death or disability, the extra amount you put in because of the rule is added to your income, and a 10% additional tax applies. If you expect to change jobs or coverage next year, the prorated figure from the HSA contribution calculator is the safer choice.
Medicare and other coverage
Months when you are enrolled in Medicare do not count, and neither do months when you have other non-HDHP health coverage, with limited exceptions such as dental, vision or certain accident coverage. If you sign up for Medicare Part A after 65, coverage can start up to six months back, so stop contributions in time to avoid an excess. The HSA contribution calculator does not test eligibility; it only does the math for the months you enter.
Married couples
If either spouse has family HDHP coverage, both are treated as having family coverage, and the $8,750 family limit is split between you as you agree. Each spouse age 55 or older gets a separate $1,000 catch-up, but it must go into that spouse’s own HSA. Run the HSA contribution calculator for each spouse’s months and add the results before you split the family limit.
If you put in too much, withdraw the excess and any earnings on it before your tax-filing deadline, including extensions. Otherwise a 6% excise tax applies each year the excess stays in the account, reported on Form 5329.
Estimates for education only, not tax, legal or financial advice. Check current rules with the tax authority or a qualified adviser.
Related converters and calculators
Related calculators:
- Salary tax calculator: take-home pay
- COBRA cost calculator: health coverage cost
- Income tax calculator: federal tax
Sources
IRS Publication 969: HSAs and other tax-favored health plans; IRS Rev. Proc. 2025-19: 2026 HSA limits; IRS: Instructions for Form 8889.
Questions about this calculator
What are the 2026 HSA limits?
$4,400 for self-only HDHP coverage and $8,750 for family coverage, plus $1,000 if you are 55 or older.
Is the age-55 catch-up prorated?
Yes. Unless you use the last-month rule, it is $1,000 × eligible months ÷ 12.
What is the last-month rule?
If you are eligible on December 1, you are treated as eligible for the whole year, so you can contribute the full annual limit.
What happens if I fail the testing period?
The extra amount allowed by the last-month rule is added to your income and a 10% additional tax applies, unless you left because of death or disability.
Do employer contributions count?
Yes. Employer contributions count toward the same annual limit.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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