I got married on July 6, 2018. Before getting married, I was on my employer's HDHP plan (with "single" coverage) and was contributing to my HSA, while my wife was NOT on her employer's HDHP (and thus not contributing to her HSA). After the marriage, we both moved to HER employer's HDHP plan, with "FAMILY" coverage, on August 3 (until August 2, I was on my employer's HDHP while my wife was on her employer's PPO).
Her employer's HSA plan is managed by Fidelity. I spoke to Fidelity customer service, and they told me that our combined HSA contribution limit would be 3450 ("single coverage" limit), pro-rated till July (bcoz I had "single" coverage until then), PLUS 6900 ("family coverage" limit), pro-rated for the remaining 5 months.
That amounts to 2,012.5 (3,450 * 7 / 12) + 2,875 (6900 * 5 / 12) = 4,887.5.
However, according to the "last-month rule", we are eligible to contribute $6900, provided we remain on "family coverage" until Dec 31, 2019.
Can someone please clarify which of the two ($4,887 / $6,900) is the limit that applies to us?
I don't think it matters, but in case it does - we will file taxes under the "married, filing separate" category for 2018.