The present value is the value of an asset today. The NumPy pv() function can calculate the present value. This function mirrors the fv() function and requires the interest rate, number of periods, and the periodic payment as well, but here we start with the future value.

Read more about the present value at http://en.wikipedia.org/wiki/Present_value. It should be easy to derive the formula for the present value from the formula for the future value, if you want.