You can make a contribution to your HSA each year that you are eligible.
For 2018, you can contribute up to:
$3,450 if you have Self-only coverage
$6,900 if you have Family coverage.
Individuals age 55 and older and not enrolled in Medicare can also make additional “catch-up” contributions. The maximum annual catch-up contribution is $1,000.
Determining your contribution
Your eligibility to contribute to an HSA is determined by the effective date of your HDHP coverage. If you do not have HDHP coverage for the entire year, you will not be able to make the maximum contribution. All contributions (including catch-up contributions) must be pro-rated. Your annual contribution depends on the number of months of HDHP coverage you have during the year (count only the months where you have HDHP coverage on the first day of the month).
For years after 2006 a special rule allows you to contribute the maximum amount for the year as long as you have coverage for December. However, if you fail to remain covered, the extra contribution above the pro-rated amount is included in income and subject to an additional 10 percent tax.
Contributions can be made as late as April 15 of the following year.