39 CFR 3030.142: CPI-U rate authority when rate adjustment filings are 12 or more months apart.

(a) If a rate adjustment filing involving a rate increase is filed 12 or more months after the most recent rate adjustment filing involving a rate increase, then the calculation of an annual limitation for the class (full year limitation) involves three steps. First, a simple average CPI-U index is calculated by summing the most recently available 12 monthly CPI-U values from the date of the rate adjustment filing and dividing the sum by 12 (Recent Average). Second, a second simple average CPI-U index is similarly calculated by summing the 12 monthly CPI-U values immediately preceding the Recent Average and dividing the sum by 12 (Base Average). Third, the full year limitation is calculated by dividing the Recent Average by the Base Average and subtracting 1 from the quotient. The result is expressed as a percentage, rounded to three decimal places.

(b) The formula for calculating a full year limitation for a rate adjustment filing filed 12 or more months after the last rate adjustment filing is as follows: Full Year Limitation = (Recent Average/Base Average)−1.