dmertz
Level 15

Deductions & credits

The method for calculating the attributable earnings is in CFR 1.408-11:

https://www.law.cornell.edu/cfr/text/26/1.408-11

 

Good luck getting an HSA custodian to do the calculation, particularly in a situation like this.  Posts in these forums indicate that many HSA custodians simply refuse to do the calculation for you and rely on you to do the calculation.