Why Standard Race Predictors Fail

Most calculators use “Riegel’s Formula” with a fixed exponent (1.06). This assumes an elite level of endurance. For a high schooler running a 17:00 5k, a standard calculator predicts a 2:42 Marathon—which is often impossible.

The “Dynamic Fatigue” Difference

Coach Saltmarsh’s race prediction calculator adjusts the math as the distance gets longer. It “penalizes” the prediction slightly for the Half and Full Marathon to account for the muscular fatigue that non-elite runners face. This gives you a safe goal, not a dream goal.

How to Use This Tool for Training

• Step 1: Enter a recent race result (within the last 6-8 weeks).
• Step 2: Select your goal distance.
• Step 3: Use the predicted time to set your “A” goal, but always train using current fitness.

Now that you know your predicted race time, calculate your daily training paces here.

Planning a marathon? Use our Mileage Builder to safely increase your volume.

Frequently Asked Questions

How accurate is this race predictor?

It is most accurate when predicting one level up, e.g., 5k to 10k. Jumping from 5k to Marathon is less precise but still a useful guideline to set realistic expectations.

Why is my predicted marathon time slower here than on other sites?

Because we value realism over optimism. We account for the “fade” that happens after Mile 20. If you are not an elite distance runner, you will fade as the distance increases.

About the Coach

Coach Saltmarsh specializes in high school distance running and athlete development. With a focus on data-driven training and consistent progression, this site provides the tools and insights coaches and athletes need to reach their peak performance. This app was built to solve a common problem for coaches: making running math simple, making the progression appropriate, and making summer training individualized and optimized for every runner on your team.

Looking for more training resources? Explore the Training Articles or view Coaching Resources.