Riegel's Race Prediction Formula
Predict your finish time for any race distance based on a recent performance.
Pete Riegel, a research engineer and avid marathon runner, developed this formula in 1977. It was first published in Runner's World magazine and quickly became the standard tool for race time prediction — valued for its simplicity and surprising accuracy across a wide range of distances.
The Formula
T2 = T1 × (D2 / D1)^1.06
- T1 — Your known race time
- D1 — The distance of that race
- D2 — Your target race distance
- T2 — Your predicted finish time
The Exponent Explained
The exponent 1.06 is a fatigue factor that captures how running performance degrades as distance increases. Riegel derived this value empirically from race data across many athletes and distances. Higher values (e.g., 1.08) may better reflect runners with less endurance base, while elite ultramarathon runners sometimes use lower values.
A Practical Example
If you ran a 5K in 25:00, Riegel's formula predicts your 10K time as:
T2 = 25:00 × (10 / 5)^1.06 ≈ 51:50
Limitations
Riegel's formula is a starting point, not a guarantee. Actual performance depends on course profile (hills, surface), weather conditions, your training for the specific distance, nutrition, and race strategy. Use it for planning, then adjust based on your experience.