In property assessment, a base year is a reference point used to determine property values. Some assessment systems value all properties as if they were sold on a specific base year date, regardless of when the actual assessment occurs. This approach aims to capture relative property values at a single point in time, making comparisons between properties fairer. When base years change (for example, moving from a 2020 base year to a 2024 base year), assessed values shift to reflect market changes over that period. Property owners may see significant assessment changes when base years are updated, even if their actual property has not changed.