Yasso 800s Calculator

About this calculator

Yasso 800s is a popular marathon-time prediction rule of thumb, credited to coach and Runner's World columnist Bart Yasso: run repeated 800m intervals and note your average time in minutes and seconds, and that same number — read as hours and minutes instead — becomes a rough prediction of your marathon finish time (for example, averaging 3:30 per 800m repeat suggests a marathon around 3 hours 30 minutes). It's an empirical shortcut rather than a physiological formula, built from Yasso's own coaching observations over many athletes and races.

Marathon runners and their coaches use Yasso 800s during training blocks as a quick fitness check and confidence gauge ahead of race day, since it requires nothing more than a track session and a stopwatch, though most coaches treat it as a rough guideline to be combined with other predictors like VDOT rather than a precise guarantee.

This calculator takes your average 800m repeat time and converts it into a predicted marathon finish time using the Yasso method.