A flexible spending account (FSA) is an account to which you make pre-tax contributions to pay for approved out-of-pocket medical expenses. Any money you contribute during the calendar year must go to pay for expenses incurred in that same calendar year. Any money left in the account at the end of the year is forfeited. Because contributions to FSAs and HSAs are tax-advantaged, or made on a pre-tax basis, federal regulations do not permit you to have both an FSA and an HSA in the same calendar year. This is something to keep in mind as you plan your benefits during your employer's open enrollment.