📈 Race Predictor Calculator
Enter a recent race result to estimate finish times for other distances and plan your training strategy.
Example: 00:24:00 for a 5K.
Lower exponent (1.03–1.05) for endurance-focused athletes; higher when endurance is a limiter.
Predicted Time
1:50:24
Target Pace
5:14 /km
8:25 /mile
Baseline Pace
4:48 /km
7:43 /mile
How to Use This Calculator
Enter recent race results
Use a race or time trial run within the past 6–8 weeks.
Pick a target distance
Select a new event to predict (5K, 10K, half, marathon, etc.).
Adjust the exponent
Lower exponent for strong endurance; higher if you fade on longer races.
Review predicted time & pace
Use results to set training targets or guide race-day pacing.
Formula
T₂ = T₁ × (D₂ ÷ D₁)ˣ
Riegel exponent x defaults to 1.06. Adjust x for individual endurance characteristics.
The Riegel formula predicts how race times scale with distance. It assumes similar race conditions and fitness levels. The exponent controls how much the time increases as distance grows; endurance athletes can use lower exponents for more optimistic predictions.
Interpreting Predictions
Use predicted paces to set realistic goals and identify weak spots. If predicted times seem aggressive, increase endurance work or adjust expectations. Always consider course profile, weather, and fueling.
Refinement Tips
- Use the most recent and well-executed race as input.
- For trail or hilly races, lower the exponent or add time buffers.
- Compare predictions with past performances to gauge accuracy.
Cross-Training Applications
- Calculate target paces for treadmill, track, or tempo sessions.
- Estimate equivalent cycling or swimming efforts by converting pace to speed.
- Use predicted times to schedule goal races and training peaks.
Frequently Asked Questions
How accurate is the Riegel formula?
It’s a widely-used heuristic. Actual results vary with fitness, terrain, weather, and race execution.
What exponent should I use?
1.06 suits many runners. Use 1.03–1.05 if you handle long races well, 1.07–1.10 if endurance is a limiter.
Can I input treadmill races?
Yes, but treadmills can be optimistic. Adjust exponent higher to account for outdoor variability.
Does this work for ultra distances?
Accuracy declines beyond the marathon. For ultras, include fueling strategy and experience-based adjustments.
Should I use chip time or gun time?
Use chip (actual) time—it reflects your personal effort without start-line delays.