100-Year Flood
Property insurance term
Definition
A flood event that has a 1% probability of occurring in any given year, not a flood that happens once every 100 years. This statistical measure defines the Special Flood Hazard Area and base flood elevation used by FEMA and the National Flood Insurance Program. Properties in 100-year floodplains face mandatory flood insurance requirements if they have federally backed mortgages. The term is often misunderstood—a 100-year flood can occur multiple times within 100 years, or not at all. Over a 30-year mortgage, a property in a 100-year floodplain has a 26% chance of experiencing such a flood.