ANSWER
Under this IRS guideline you must use your full election amount by the end of the plan year. Any remaining balance in your account will be forfeited. However, the IRS has relaxed this rule. Your employer has the option to adopt a provision that will allow a portion of leftover Health FSA funds at the end of the year to be carried forward to the next plan year (the IRS updates the maximum carryover amount annually).
We encourage participants to plan carefully how much money they put into their account. Be conservative when selecting your annual election amount. Only calculate expenses you anticipate incurring. This can include expenses such as co-payments for prescriptions, vision expenses, and dental work. For help calculating your expenses check out this FSA Calculator here.