(a) Increase based on the CPI. We compute the average of the CPI for the quarters that begin and end the measuring period by adding the three monthly CPI figures, dividing the total by three, and rounding the result to the same number of decimal places as the published CPI figures. If the number of decimal places in the published CPI values differs between those used for the beginning and ending quarters, we use the number for the ending quarter. If the average for the ending quarter is higher than the average for the beginning quarter, we divide the average for the ending quarter by the average of the beginning quarter to determine the percentage increase in the CPI over the measuring period.

(b) Increase based on the AWI. If the AWI for the year that ends the measuring period is higher than the AWI for the year which begins the measuring period and all the other conditions for an AWI-based increase are met, we divide the higher AWI by the lower AWI to determine the percentage increase in the AWI.

(c) Rounding rules. We round the increase from the applicable paragraph (a) or (b) of this section to the nearest 0.1 percent by rounding 0.05 percent and above to the next higher 0.1 percent and otherwise rounding to the next lower 0.1 percent. For example, if the applicable index is the CPI and the increase in the CPI is 3.15 percent, we round the increase to 3.2 percent. We then apply this percentage increase to the amounts described in § 404.271 and round the resulting dollar amounts to the next lower multiple of $0.10 (if not already a multiple of $0.10).

(d) Additional increase. See § 404.278 for the additional increase that is possible.