Short answer: Your HSA contribution limit is usually prorated based on the number of months you’re eligible, unless you qualify for the last-month rule and remain eligible through the following year.
If you are only eligible to contribute to a Health Savings Account for part of the year, the IRS generally requires your annual contribution limit to be prorated based on how many months you were HSA-eligible.
Under the standard proration method, you divide the annual HSA contribution limit by 12 and multiply it by the number of months you were eligible. A month counts if you are HSA-eligible on the first day of that month.
For example, if you had self-only HSA-eligible coverage for 6 months in 2026, your maximum contribution would be $4,400 ÷ 12 × 6, or $2,200.
There is an important exception called the last-month rule. If you are HSA-eligible on December 1, you may contribute up to the full annual limit for that year, even if you were not eligible for the entire year.
However, to use the last-month rule, you must remain HSA-eligible through the entire following calendar year. This period is known as the testing period. If you fail the testing period, the extra contributions become taxable and may be subject to a penalty.
If your eligibility changes during the year and your future coverage is uncertain, prorating your contributions is generally the safest approach.
Sources
- IRS, FAQs on Health Savings Accounts – Partial-Year Eligibility: https://www.irs.gov/faqs/health-savings-accounts-hsas
- IRS, Publication 969 – Health Savings Accounts (Last-Month Rule): https://www.irs.gov/forms-pubs/about-publication-969
Content history
Originally published: March 27, 2025
Last reviewed: January 26, 2026