If you hear someone yell "Hey Geek", do you turn around? If so, keep reading. This page is using Javascript to do the calculations. While Javascript has been around for a while, some of the older browsers do not support this. The Pace Calculator and Estimator use a formula developed by Runner's World. Basically, it assumes a 5% reduction in Pace each time the distance doubles. For the math folks, try T2 = T1 * ((D2/D1)**1.07), where T = time and D = Distance for 1st and 2nd runs.