The purpose of the COLA is to ensure that the purchasing power of Social Security and Supplemental Security Income (SSI) benefits is not eroded by inflation. It is based on the percentage increase in the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W) from the third quarter of the last year a COLA was determined to the third quarter of the current year. If there is no increase, there can be no COLA. The CPI-W is determined by the Bureau of Labor Statistics in the Department of Labor. By law, it is the official measure used by the Social Security Administration (SSA) to calculate COLAs.