Cost-of-living adjustments (COLAs) for the Civil Service Retirement System (CSRS) and the Federal Employees Retirement System (FERS) are based on the rate of inflation as measured by the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W). COLAs for both CSRS and FERS are determined by the average monthly CPI-W during the third quarter (July to September) of the current calendar year and the third quarter of the base year, which is the last previous year in which a COLA was applied.