Race time predictor
From a recent race time, estimate your 5K, 10K, half marathon and marathon times.
How it works
Riegel formula: T2 = T1 × (D2 / D1)^1.06. It assumes training suited to the target distance (especially for the marathon).
Results are for guidance only and do not replace professional advice.
Worked example
With the default values:
- Distance run10 km
- Your time (h:mm:ss or mm:ss)52:30
you get:
- Marathon4:01:31 (5:43 min/km)
- 5 km25:11 (5:02 min/km)
- 10 km52:30 (5:15 min/km)
- Half marathon1:55:50 (5:29 min/km)
Frequently asked questions
How does the “Race time predictor” tool work?
Riegel formula: T2 = T1 × (D2 / D1)^1.06. It assumes training suited to the target distance (especially for the marathon).
What do I need to enter?
Just fill in: distance run, your time. The result updates as you type.
Can you give an example?
Distance run: 10 km; Your time (h:mm:ss or mm:ss): 52:30 → Marathon: 4:01:31 (5:43 min/km); 5 km: 25:11 (5:02 min/km).
Is this calculator free, and is my data private?
Yes. HOD Calc is completely free with no sign-up. The calculation runs in your browser: nothing you type is sent or stored.