I was contributing to an HSA for family coverage. In June 1st my family changed coverage while I stayed with the HSA. Would my max contribution be $6,425 for 2025?

[vicente]

I received a message from my bank saying that I exceeded my maximum contribution now that I am enrolled as an individual because I have gone over $4,300, but my understanding is that I should be able to prorate and contribute the maximum for a family during the first half of the year, and the maximum for and individual the second half. With this, the max would be $6,425.

[Mike9241]

The annual limit on HSA contributions for self-only coverage in 2025 will be $4,300, a 3.6 percent increase from the $4,150 limit in 2024, the IRS announced May 9. For family coverage, the HSA contribution limit will jump to $8,550, up 3 percent from $8,300 in 2024.

8550*5/12 +4300*7/12= 6071

note we know nothing about the coverage the rest of the family had starting 6/1 for example if your spouse had a flexible savings health savings account effective 6/1 that would bar you from making any contribution for that portion of 2025

[Opus 17]

Assuming that you were covered by a family HDHP for 5 months (coverage is determined on the 1st day of each month) and a single HDHP for the other 7 months, your contribution limit for 2025 would be 

$8550 ÷ 12 x 5 months = $3562.50

$4300 ÷ 12 x 7 month = $2508.33

For a total of $6060.83 ($6061 since the IRS rounds up).

However, this assumes you have no "other coverage."  Having "other coverage" besides the HSA makes you completely ineligible to contribute to an HSA.  Other coverage would include, if your spouse has a family plan and you are covered by it, even if it is secondary to your own plan.  Other coverage also includes most FSAs (flexible spending accounts) because if your wife took an FSA, it can be used to cover you as well, even if you are not the named insured.

Your coverage controls your contributions, not your wife's coverage (except for the disqualification due to other coverage).  For example, if your wife enrolled in her new job's insurance effective June 1, but your HDHP coverage did not change over to single until June 15, then your limit would be $6425, because your eligibility is determined by your coverage on the first day of each month.