HSA contribution limit calculator: partial year, last-month rule, Medicare

Started a high-deductible plan mid-year, switched between self-only and family coverage, or enrolled in Medicare? Enter your coverage on the first day of each month and see your HSA limit for the year: month by month, and under the last-month rule, with what you'd owe if you fail its testing period.

✓ TestedMatches the IRS examples in Publication 969

Your HSA limit for the year–

Month by month: each month you're eligible on the first day adds a twelfth of that month's limit (self-only or family), plus a twelfth of $1,000 from 55; months on Medicare add nothing. Last-month rule: if you're eligible on December 1, you may instead treat the whole year as having December's coverage, but you must then stay eligible through December 31 of the next year (the testing period). Married with family coverage: the family part is split between your HSAs (equally unless you agree otherwise); the $1,000 catch-up isn't shared and goes in your own HSA. Employer contributions count toward your limit. Source: IRS Publication 969 and the Form 8889 instructions.

How it works

Your HSA limit is worked out month by month, as on the Form 8889 Limitation Chart: each month you are an eligible individual on the first day adds a twelfth of the self-only or family limit, and from 55 a twelfth of the $1,000 catch-up. Months on Medicare add nothing. If you are eligible on December 1, the last-month rule lets you use December's coverage for the whole year instead, but only if you stay eligible until the end of the next year. The IRS examples in Publication 969 give the same results here: family coverage from December 1, 2025 allows $8,550 under the rule, against $712.50 month by month, so failing the testing period makes $7,837.50 taxable, plus a 10% additional tax. More in the partial-year HSA guide.

HSA contribution limit calculator: partial year, last-month rule, Medicare

How it works

Worked examples