My husband was covered by my employer-provided HSA-eligible HDHP from January through April of 2025. I calculated our allowable family contribution as $8,550 + $1,000 (catch-up for myself) for a total of $9,550 x 4/12 (pro-rating for the 4 months we were on my plan), for a contribution limit of $3,183. I retired at the end of April and went on Medicare. He joined his employer's non-eligible health plan from May through July. He began a new job at the end of July and has been covered by an HSA-eligible HDHP for himself from August 1 through December. I come up with a contribution limit for him of $4,300 + $1,000 (catch-up for himself) for a total of $5,300 x 5/12 (pro-rated for the 5 months on his HDHP) for a contribution limit of $2,208. Since he was covered by his HDHP on Dec 1, can we apply the "Last-Month Rule" to increase his contribution limit to cover the 3 months (May-July) that he was on his non-eligible plan and not covered by my HDHP? Effectively, that would be applying the Last-Month Rule, to 2025 but subtracting the 4 months (Jan-April) that he was covered by my HDHP. Is this calculation correct?
