In order for a medical expense to be eligible for reimbursement from a Health Savings Account (HSA), the expense must have been incurred after the opening of your HSA account. So, for example, suppose you opened an HSA account on 1/1/2021 and funded it with $100. You paid the $2,500 with funds outside the HSA. In January 2022, you contributed $3,000 to your HSA account. Then you request an HSA reimbursement for the $2,5000 incurred in 2021. This is allowed.
