Calving Interval is the number of days between the most recent and the second-most-recent calving. Cows with consistently long calving intervals may fail to rebreed under fixed breeding season management. Evaluating the average calving interval in a herd may help the breeder identify areas for management improvement. Lifetime average calving interval is calculated as the number of days between first and last calving divided by the number of calvings. It is a useful indicator of herd reproductive performance.