A price index is a normalized average of price relatives for a given class of goods or services in a given region, during a given interval of time. It is a statistic designed to help to compare how these price relatives, taken as a whole, differ between time periods or geographical locations.

Cost of living is the cost of maintaining a certain standard of living. Changes in the cost of living over time can be operationalized in a cost-of-living index. Cost of living calculations are also used to compare the cost of maintaining a certain standard of living in different geographic areas. Differences in cost of living between locations can be measured in terms of purchasing power parity rates. A sharp rise in the cost of living can trigger a cost of living crisis where purchasing power is lost and the previous lifestyle is no longer affordable.