Since the HSA custodian is to calculate the investment gain or loss on the contribution that is being returned, the request for a return of excess contribution before the due date of your tax return (including extensions) should generally be made to the HSA custodian of the account to which the excess contribution was made. However, sometimes the request cannot be made with the corresponding HSA custodian, say, because in the mean time the HSA was moved to a different custodian. In that case the HSA custodian should ask you to determine the investment gain or loss attributable to the contribution being returned.
