This is your personal decision.  We do however recommend that you elect what you know you will owe for expenses you expect to have provided in the upcoming Plan Year.  It is not advisable for you to guess at this amount.  Generally, you can predict some known expenses such as prescription costs for the year, eye exams, glasses and contacts, orthodontics payments, scheduled dental work or scheduled surgeries.  Any amount you elect beyond this educated guess is a little risky. 

Your goal is to get the tax advantage (25 – 40% savings on each dollar) on as much as you can reasonably predict.  This way, you at least save taxes on the bulk of your expenses.  There is no way to predict illness or accidents.  Therefore, you shouldn’t elect dollars for these type of expenses.