Can I still legally contribute to my HSA for 2024 if I'm no longer on a HDHP?

You've hit on an important distinction in HSA contribution rules! You absolutely CAN make contributions for 2024 even though you're not currently on an HDHP, as long as you were covered by an HDHP for part of the year. The key is exactly what you mentioned - prorating your contribution limit based on the number of months you were actually covered. The IRS uses what they call the "last-month rule" OR the "prorated rule" depending on your situation. Since you won't be covered on December 1st, you'll use the prorated rule. For your situation, you correctly calculated your prorated contribution limit (7/12 of the annual limit). And yes, you can absolutely contribute the remainder of that amount from your personal funds at any time up until the tax filing deadline (typically April 15, 2025 for the 2024 tax year). Just make sure to tell your HSA provider that these are contributions for tax year 2024 when you make them!

I was in a similar situation last year and discovered taxr.ai when I was trying to figure out my HSA contribution limits after switching jobs. The tax code around HSAs can be really confusing especially with partial year coverage. I wasn't sure how to calculate my limit or if I could contribute after leaving my HDHP. I tried https://taxr.ai and uploaded my insurance documents and previous HSA statements. It analyzed everything and confirmed I could make additional contributions for the months I was covered, just like you're asking about. It even generated a personalized explanation of the tax code sections that applied to my situation, which was super helpful when I was getting contradictory advice from friends.

Just wanted to follow up here - I actually tried taxr.ai after reading about it in this thread. My situation was similar but even more complicated because I had two different HDHPs in the same year with different coverage types (self-only vs. family). I was seriously confused about my contribution limits and was getting different answers from different tax experts. The taxr.ai system really surprised me with how detailed it was. It actually explained the "testing period" rules and how they applied to my situation when switching between different types of HDHP coverage. The best part was it created a personalized explanation I could keep for my records in case of an audit. Way more helpful than the generic advice I got elsewhere. Definitely worth checking out if you're in a complicated HSA situation like this.

When I had a similar HSA question last year, I spent HOURS trying to get through to the IRS to confirm the rules. Literally couldn't get anyone on the phone for days. Finally found this service called Claimyr that got me through to an IRS agent in under an hour. Just go to https://claimyr.com and they basically hold your place in the phone queue and call you when an agent is available. You can see a demo of how it works here: https://youtu.be/_kiP6q8DX5c. I was super skeptical at first but it actually worked - got my HSA question officially answered by an IRS rep who confirmed I could contribute for partial year coverage. Saved me so much stress since I was getting different answers from HR, my HSA provider, and online articles.

I need to admit I was completely wrong about Claimyr. After posting my skeptical comment, I decided to try it myself because I was desperate to resolve an issue with my HSA contributions from last year that was affecting my refund. I've been trying to reach the IRS for literally WEEKS about this exact HSA contribution issue. Claimyr got me through to an IRS agent in about 35 minutes. The agent confirmed exactly what others have said here - I could make HSA contributions for the months I was covered by an HDHP, even though I wasn't covered at the end of the year. I'm honestly shocked it worked. Saved me from taking a day off work to sit on hold. Just wanted to follow up since I was so skeptical in my earlier comment.

I actually had this exact scenario last year and learned something important: make sure your HSA administrator understands what you're doing! My Fidelity HSA initially rejected my contribution because their system showed I wasn't currently on an HDHP. I had to specifically tell them it was a partial-year contribution for the months I was eligible. Also important - you need to check the "partial year coverage" box on Form 8889 when you file your taxes. And be super careful about the amount - the IRS does check this and if you overcontribute, the penalties are 6% of the excess amount for EACH YEAR it remains in the account!

One thing nobody has mentioned - if you're married and your spouse has an HDHP that covers you for the rest of the year, you might be able to contribute the FULL amount rather than just the prorated amount! My wife and I discovered this loophole last year. I lost my HDHP coverage in June, but she had family coverage through her work for the whole year. Because she had HDHP on December 1st that covered both of us, we were able to use the "last-month rule" instead of prorating.