If you were an eligible HSA participant for the entire tax year and your HDHP coverage changed during the year (for example, you switched from self-only coverage to family coverage, or vice versa), enter the larger of these two amounts:
- The limitation amount shown on the final line of the IRS HSA limitation worksheet.
- The maximum HSA contribution limit based on the type of HDHP coverage you had on the first day of the last month of the tax year (generally December 1 for calendar-year taxpayers).
The IRS allows a special rule, often called the "last-month rule," that may let you contribute more than the amount calculated month by month if you were HSA-eligible on the first day of the last month of the year.
If you were not an eligible individual on the first day of the last month of your tax year, use the IRS Line 3 Limitation Chart and Worksheet to calculate the correct amount to enter.
Keep in mind that contributing more than your allowed limit can result in excess contributions and potential tax penalties. If your coverage changed during the year, taking a few extra minutes to calculate the correct limitation can help you avoid problems later.