The IRS sets the maximum contribution limits for the HSA each year. The maximum annual contribution limit for 2018 is $3,450 if you are enrolled in Individual coverage and $6,850 if you are enrolled in Family coverage. Once you are over the age of 55, you can contribute an additional $1,000 above the standard annual maximum. (Note: if both spouses are over the age of 55, each spouse would need have their own HSA to contribute the $1,000 catch-up)
If your HDHP was effective on January 1st, the total amount you can contribute to your account is the maximum contribution amount set by the IRS. If your HDHP is effective after the first day of the month, you may make or receive a full year’s contribution to your HSA for partial year coverage as long as you maintain your HDHP enrollment for 12 months. If enrollment is less than 12 months, the tax benefit is lost and a 10% penalty is imposed.