You have up until the day that you stopped your contributions to “incur” the expense, which means for the expenses to apply. But you have until April 30 the following year to submit a request for reimbursement unless you terminate employment sooner. This is because the tax benefit associated with having the account ended as of your last contribution, so as a penalty, the IRS will say that you can’t indefinitely reimburse from tax free money. If you want the benefit of having contributions for transportation available at any time, you should change your pledge to $1 a month so you can indefinitely have the money available. Once you spend the funds in the account, you should then cancel.