Calculating Index Changes

Calculating Index Changes

Movements of the indexes from one month to another are usually expressed as percent changes rather than changes in index points, because
index point changes are affected by the level of the index in relation to its base period while percent changes are not.

The example below illustrates the computation of index point and percent changes.

Percent changes for 3-month and 6-month periods are expressed as annual rates and are computed according to the standard formula for
compound growth rates. These data indicate what the percent change would be if the current rate were maintained for a 12-month period.

example
Index Point Change

CPI 202.416
Less previous index 201.800
Equals index point change .616


Percent Change

Index point difference .616
Divided by the previous index 201.800
Equals 0.003
Results multiplied by one hundred 0.003x100
Equals percent change 0.3