Race Time Predictor Calculator
Estimate your future race performance with the Race Time Predictor using the Riegel formula. Enter your recent race time and distance, and predict how long it would take to run longer (or shorter) races. Ideal for 5K, 10K, half-marathon, or marathon planning based on real performance.
Predict Race Performance from Past Results
Riegel Prediction Formula
$$T_2 = T_1 \times \left( \frac{D_2}{D_1} \right)^{1.06}$$
Where:
- $$T_1$$ = time for known distance D1D1
- $$T_2$$ = predicted time for target distance D2D2
- Exponent 1.06 is standard for endurance prediction based on Riegel’s analysis
Race Time – Calculation Example
Example:
- You ran 10 km in 52 minutes
- You want to predict your half-marathon (21.0975 km) time
- $$T_2 = 52 \times \left( \frac{21.0975}{10} \right)^{1.06} = 52 \times (2.10975)^{1.06} \approx 52 \times 2.209 \approx 114.87$$
So, predicted half-marathon time = 114.87 minutes ≈ 1 hour 54 minutes
The Riegel formula is a reliable way to forecast running performance based on prior race results. It assumes that your endurance and pacing are consistent. This tool works best when:
- The reference race and target race are similar in effort
- The base time is from a recent race
- You maintain a similar level of training
Common uses:
- Predict marathon time from a 10K
- Estimate 5K pace from a 3K result
- Plan split goals for long races