The number of periods of annuity calculator is used to calculate the total number of periodic value one has to make or save based on a future value with known payment and rate of interest. Where, an annuity is the series of equal payments made at the end of each period over a fixed amount of time. The period here refers to the number of periods of annuity. The future value of an annuity is the value of a group of recurring payments at a specified date in the future.