The Science Behind Race Prediction

This calculator uses the Riegel Formula, developed by researcher Pete Riegel in 1977 and still considered one of the most accurate race prediction methods:

T2 = T1 × (D2/D1)^1.06

Where:

• T1 = Your known race time
• D1 = Distance of known race
• T2 = Predicted time
• D2 = Target race distance

Why the Exponent is 1.06

The 1.06 factor accounts for the fact that you can't maintain the same pace as distance increases. It represents the average "fatigue factor" across runners. Elite runners may have a lower factor (better endurance), while newer runners may have a higher factor.

Important Caveats

Predictions Become Less Accurate When:

1. Distance gap is large - Predicting a marathon from a mile time is less reliable than from a half marathon
2. Training doesn't match - A 5K specialist may underperform marathon predictions
3. Conditions vary - Heat, hills, and wind significantly affect longer races
4. Experience differs - First-time marathoners often slow more than predicted

For Best Accuracy:

• Use a race distance within 2-3x of your target
• Ensure the source race was a true all-out effort
• Factor in course difficulty and expected conditions
• Add 2-5% buffer for first attempts at a new distance

Common Prediction Examples

From	To	Multiplier (approx)
5K	10K	2.08x
5K	Half	4.65x
5K	Marathon	9.8x
10K	Half	2.22x
10K	Marathon	4.7x
Half	Marathon	2.1x