A flexible spending account (FSA), also known as a flexible spending arrangement, is one of a number of tax-advantaged financial accounts that can be set up through a cafeteria plan of an employer in the United States. An FSA allows an employee to set aside a portion of earnings to pay for qualified expenses as established in the cafeteria plan, most commonly for medical expenses but often for dependent care or other expenses. Money deducted from an employee's pay into an FSA is not subject to payroll taxes, resulting in substantial payroll tax savings. Before the Patient Protection and Affordable Care Act, one significant disadvantage to using an FSA was that funds not used by the end of the plan year were forfeited to the employer, known as the use-it-or-lose-it rule. Under the terms of the Affordable Care Act, a plan may permit an employee to carry over up to $500 into the following year without losing the funds.

The most common type of flexible spending account, the medical expense FSA (also medical FSA or health FSA), is similar to a health savings account (HSA) or a health reimbursement account (HRA). However, while HSAs and HRAs are almost exclusively used as components of a consumer-driven health care plan, medical FSAs are commonly offered with more traditional health plans as well. In addition, funds in an HSA are not lost when the plan year is over, unlike funds in an FSA. Paper forms or an FSA debit card, also known as a Flexcard, may be used to access the account funds.