Auto insurance customers can be transitioned from an initial rating algorithm A to a subsequent algorithm B by phasing in the transition over a period of several years. The premium charged during the transition period is equal to the premium calculated under the rating algorithm B minus a premium adjustment. The premium adjustment is given by the difference between the premium according to algorithm B minus the legacy premium from algorithm A, said difference being multiplied by a rating transition factor. The rating transition factor may be a linearly decreasing function which has a value of 1 just before the transition period and a value of zero at the end of the transition period. The transition period may be in the range of 3 to 8 years long.