HSAs are your money regardless once you have it (except management fees). So you can spend it until it is gone. FSAs are a very specific set aside for a single

HSAs are your money regardless once you have it (except management fees). So you can spend it until it is gone. FSAs are a very specific set aside for a single year of billing, you can neither spend it on a bill for say, December the year before, nor use it for medical care in January the year after.