Tax Question - HSA contributions while accidentally covered by 2 health insurance plans
I recently enrolled in an HDHP plan through my employer that became effective in January 2026. I and my employer both started contributing to an HSA the following month in February. I later found out that I was dual-covered by a second health insurance plan through my parents (a non-HDHP plan that would've made me ineligible for an HSA) that I did not know I was still on. That plan was dropped in March 2026 as I was turning 26 anyways and wouldn't have been able to remain on it even if I had wanted to.
My current HDHP plan provider reached out in March and was going to drop me because of the dual-coverage, but I clarified that the other plan was being dropped and they "let everything ride" but told me to check with a financial advisor about the tax implications of contributing to an HSA while being dual-covered. I checked with a financial advisor and he suggested that I have both my own and my employers' contributions from Jan - March refunded and then re-contribute those contributions now that I am only covered by the HDHP plan (he mentioned I would still be eligible for the full $4400/year limit but should just make sure all of my contributions are listed as post-March).
Doing additional research, I dug into the "last month" rule, and this info seemed to indicate that it does not matter what month my contributions are from as long as I am enrolled in the plan on December 1, 2026, and remain enrolled through all of 2027 (which I plan to do). I have tried reaching out to the IRS hotline for questions along with the company that runs my HSA but have been unable to get an answer from them. I finally got through to my HDHP plan provider today and they suggested that I do not need to adjust my contributions at all and am still eligible for the full $4400/year amount this year.
I'm trying to ensure that I didn't break any HSA/tax rules on accident (and avoid any tax penalties due to those HSA contributions from Feb/Mar) and/or to ensure that I rectify the situation if I did so. My current thought is that I can still contribute the full $4400 this year without any penalty (as long as I keep the plan through all of next year), and I do not think I need to remove and re-contribute my HSA contributions from Feb/Mar since the month the contributions were made in doesn't appear to matter for tax implications. Thus, I am looking for some help to clarify if this thinking is correct. Or, do I instead need to contribute less for the year or refund and re-contribute my HSA funds that were added while I was still dual-covered? Any help is very appreciated. Thank you in advance!