Three key rules about flex plans
1. Use it or lose it
If there is any money left in your account after the run-out period has passed, any remaining amounts are lost to you and revert to the plan. This is sometimes referred to as the Use It or Lose It Rule. Therefore, be conservative and put in your account only what you are certain you will use.
This applies to any flex spending program, including Dependent Care Reimbursement Accounts, Medical Reimbursement Accounts, Private Premium Accounts, and Dental & Vision Accounts.
This rule does NOT apply to Health Savings Accounts and Health Reimbursement Accounts.
2. Allowed changes in the middle of the year are very limited
3. You have to re-enroll once a year.
The "annual enrollment" period is when you are allowed to more easily change the amount you have in your flex account. Each organization has an open enrollment period before the plan year begins, usually several weeks before the plan year begins. Mark your calendar.