India's CPI 2024 base halves back series index, inflation unchanged

Shift to CPI 2024 base sharply lowers headline index levels in back series, but inflation rate remains identical across rural and urban segments

India’s shift to the Consumer Price Index (CPI) 2024 base year has sharply lowered the headline index level for the back series compared with the 2012 series — effectively cutting it nearly in half — while leaving the inflation rate unchanged. 

Under the 2012 series, the combined CPI stood at 150.2 in January 2020. Under the 2024 series, the same month reads 79.11. By December 2025, the index prints at 198 under the old base and 104.29 under the new one. The pattern is similar across rural and urban segments, with index levels compressed to nearly half their earlier magnitude. 

The adjustment reflects the official linking factors — 0.5267 for the combined index, 0.5222 for rural, and 0.5320 for urban — used to rescale the older series to the new base year. This statistical reset alters the level of the index, not its movement. 

The shift may appear dramatic at first glance, with the index effectively compressed to a new scale. However, inflation — measured as the rate of change — remains identical under both series. 

This outcome follows from the use of constant linking factors. Because each observation in the old series is multiplied by the same factor, percentage changes between periods are preserved. The base shifts; the growth rate does not.