By default your limit is prorated by the sum-of-months method. The IRS tests eligibility on the first day of each month, so a month only counts if you were HSA-eligible on the 1st — coverage that takes effect on June 15, for example, makes July your first counting month, not June. Your limit is then the sum, over each qualifying month, of that year's annual limit for your coverage type divided by twelve. For 2026 that's $366.67 a month for self-only and $729.17 a month for family. Six qualifying months of self-only coverage in 2026 gives $2,200.

If you're HSA-eligible on December 1, the last-month rule lets you be treated as eligible for the entire year — so you can contribute the full annual limit even if you were only covered for part of it. It's genuinely useful, but it isn't free: it comes with a testing period. You must remain HSA-eligible through December 31 of the following year. If you don't, the amount you contributed above what the sum-of-months method would have allowed gets added back to your taxable income and hit with an extra 10% tax. The calculator shows both figures side by side so you can weigh the full-year amount against the safe, no-strings sum-of-months amount.

Each month is valued by the coverage you had on its first day, so months on self-only use the self-only rate and months on family use the family rate. But if you have family coverage on December 1, the last-month rule can let you contribute the full family limit for the whole year — provided you meet the testing period. The IRS's own example: self-only for most of the year, switching to family coverage that's in place on December 1, allows the full family limit. The calculator reports the greater of the two methods, exactly as Form 8889 does.

Yes. The limit is a single combined cap across every source. Anything your employer puts in — including matching or wellness contributions and anything you route through payroll — counts toward the same limit, so subtract it before deciding how much to add yourself. Going over the limit triggers a 6% excise tax (IRC §4973) for each year the excess stays in the account, so it's worth getting right.

If you're 55 or older during the year you can add a $1,000 catch-up. It's fixed by statute and, unlike the main limits, is not adjusted for inflation — it's been $1,000 for years and is the same for 2025 and 2026. It prorates the same way as the base limit under the sum-of-months method. One catch that surprises couples: the catch-up can only go into the HSA of the person who is 55+, so if both spouses want to make catch-up contributions, each needs their own HSA in their own name.

Enrolling in Medicare — including premium-free Part A — ends your HSA eligibility, and your contribution limit drops to zero starting the month you enroll. Watch the six-month retroactive rule: when you claim Social Security or enroll after 65, Part A coverage is backdated up to six months, so you should generally stop HSA contributions six months before you apply. Contributions made during a period Medicare retroactively covers become excess contributions.

No. The calculator runs entirely in your browser and stores nothing on our servers — there's no email box and no sign-up. Your inputs are only reflected in the page's web address so you can bookmark, share, or print your result; clear the link and they're gone.