If you’re only eligible for part of the year, your annual HSA contribution limit is usually prorated based on the number of months you were HSA-eligible.
🧮 How Proration Works:
Divide the annual contribution limit by 12 and multiply by the number of months you were eligible.
Example: If you had self-only coverage for 6 months in 2025, your max contribution would be:
$4,300 ÷ 12 × 6 = $2,150
⚠️ The Last-Month Rule:
There’s one exception: if you’re HSA-eligible on December 1, you can contribute up to the full annual limit, even if you weren’t eligible all year.
But—you must stay HSA-eligible through the end of the next calendar year (called the testing period) or risk a tax penalty on the extra contributions.
🧠 Key Tip:
If your HSA eligibility changes during the year, prorating your contributions is the safest route—unless you’re sure you’ll stay eligible long enough to meet the last-month rule.