Per
IRS Publication 969, "Self-only HDHP coverage is HDHP coverage for only an eligible individual. Family HDHP coverage is HDHP coverage for an eligible individual and at least one other individual (whether or not that individual is an eligible individual)."
An "eligible individual" is defined as follows:
To be an eligible individual and qualify for an HSA, you must meet the following requirements.
- You are covered under a high deductible health plan (HDHP), described later, on the first day of the month.
- You have no other health coverage except what is permitted under Other health coverage , later.
- You aren’t enrolled in Medicare.
- You can’t be claimed as a dependent on someone else’s 2018 tax return.
If you meet those four bullet points above, you're an eligible individual. If your health insurance covers you and at least one more person, it's considered family coverage for the purpose of HSA contribution limits.
Family plan = Family limit.
If you're DH is on an HDHP plan with separate HSA he could also contribute up to an individual amount.
This last bit isn't true. See
this section in the publication. Married couples must share a single family-sized contribution limit. They can split their $6,900 however they like between their two HSAs, but they cannot contribute more than $6,900 in aggregate.
However there is an interesting loophole here where people who are unmarried but share family HDHP coverage are each eligible for their own family-sized HSA contribution. The special rule where two adults must split the contribution limit only applies to married people. This loophole can apply in the case of someone whose employer lets their unmarried partner join the company health insurance. It can also happen for adults under 26, who are no longer tax dependents of their parents, but remain on their parents' health insurance plan. In either case, there are two (or maybe more) people who meet the four bullet points for being an "eligible individual," all are covered by a family HDHP plan, and they are not married. Each of these people can contribute $6,900 to their own HSA.