If you forfeit DCFSA benefits (they are left in your account and you don't have any qualifying claim to submit for reimbursement), then the money is just lost. There is no penalty, and the forfeited benefit is not taxable, but you don't get the money back. Turbotax will cover this situation. If you have a benefit in box 10 of your W-2, you will be required to go through the dependent care interview, which will include a question about forfeited amounts.