Predict Your Marathon Time
You can estimate a longer race finish from a recent shorter one using Riegel's formula, which scales your time by the distance ratio raised to the power 1.06. That small exponent captures a key truth of endurance running: pace slows as distance grows, so you can't just multiply.
From 10K to marathon
Plug in a recent, hard 5K, 10K, or half result and the calculator projects your marathon and half times. The prediction is only as good as the effort you enter — a casual jog underestimates you, an all-out race gives a realistic ceiling. Riegel tends to be quite accurate across nearby distances and slightly optimistic for big jumps.
Training makes the prediction real
The formula's crucial assumption is that you've trained appropriately for the target distance. A fast 10K runner who hasn't built marathon endurance will finish well behind the prediction, because the marathon punishes missing long runs and fueling practice. Use the number as a goal that your training has to earn, not a guarantee — and pace conservatively early.
Frequently asked questions
- How accurate is a marathon time predictor?
- Quite accurate between nearby distances if you've trained for the target; it's optimistic for big jumps without the endurance base.
- What race should I enter?
- A recent, hard 10K or half marathon gives the most realistic marathon projection.
- Why can't I just multiply my 10K time?
- Pace slows with distance. Riegel's exponent of 1.06 accounts for that fade.