Per IRS Publication 969 Health Savings Accounts and Other Tax-Favored Health Plans, on page 6:
Limit on Contributions
The amount you or any other person can contribute to your HSA depends on the type of HDHP coverage you have, your age, the date you become an eligible individual, and the date you cease to be an eligible individual. For 2020, if you have self-only HDHP coverage, you can contribute up to $3,550. If you have family HDHP coverage, you can contribute up to $7,100.
On page 7:
Rules for married people. If either spouse has family HDHP coverage, both spouses are treated as having family HDHP coverage. If each spouse has family coverage under a separate plan, the contribution limit for 2020 is $7,100. You must reduce the limit on contributions, before taking into account any additional contributions, by the amount contributed to both spouses’ Archer MSAs. After that reduction, the contribution limit is split equally between the spouses unless you agree on a different division.
CAUTION! The rules for married people apply only if both spouses are eligible individuals.
If both spouses are 55 or older and not enrolled in Medicare, each spouse’s contribution limit is increased by the additional contribution. If both spouses meet the age requirement, the total contributions under family coverage can’t be more than $9,100. Each spouse must make the additional contribution to his or her own HSA.
Due to the many combinations of allowable contribution limits, TaxAct is not able to compute the overall HSA contribution limit when there are two Forms 8889 present on the return. The user will need to review the Form Instructions on the screen titled Health Savings Accounts – Separate HSAs and Family Coverage to determine the Portion of Contribution Limit Allocated to [Taxpayer or Spouse]’s 8889 amount to enter. You may also wish to click the info icon on this page to review the Contribution Limit Chart.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.