Race Time Predictor
Predict finish times across 5K, 10K, half and full marathon from one recent race, using the Riegel formula and VDOT-style equivalent performances. An estimate — predictions get less reliable the further the distance from your known result.
Your time for that race
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Your equivalent race times
5K 23:59 · Marathon 3:50:01
Predicted from your 10 km time of 50:00 using the Riegel formula.
| Distance | Predicted time | Pace /km |
|---|---|---|
| 5K | 23:59 | 4:48 |
| 10K (your race) | 50:00 | 5:00 |
| Half marathon | 1:50:19 | 5:14 |
| Marathon | 3:50:01 | 5:27 |
Equivalent performances assume the same fitness and similar course conditions. In practice, endurance and fuelling matter more as distance grows, so marathon predictions from a 5K are the least reliable.
Formula & source — Riegel formula (Riegel, 1981)
T₂ = T₁ × (D₂ ÷ D₁)^1.06 for each target distance. Published by Peter Riegel in Runner's World (1981). An estimate, not a guarantee.
Estimate, not medical advice. FitCalc results are estimates based on population-average formulas. They are not a diagnosis, a prescription, or a substitute for professional medical advice. If you have a medical condition, are pregnant, or take medication, talk to a doctor or registered dietitian before changing your diet or exercise. FitCalc claims no medical credentials.
Try next: Pace Calculator · 5K Pace Calculator · 10K Pace Calculator