Race predictor
Estimate your performance on a target distance from your personal records (Riegel).
📖 Guide
- Select the sport: Currently this is running only
- Select the target distance: Choose a distance
- Enter a personal record: Input at least one record
- Submit: The Riegel algorithm will compute your estimated time.
🔬 The Riegel equation predicts performance based on your history. More recent records = more accurate.
T₂ = T₁ × (D₂ / D₁)^1.06
The exponent 1.06 models how pace degrades as distance increases.
⚡ Common use cases
- Marathon goal: Enter your recent 10K to estimate your probable marathon time.
- Plan a season: Compare estimations across distances.
- Track progress: Better records = faster estimates
💪 Sport
👣 Distance
⏱️ Personal records
🎯 Target time (optional)
How the Riegel algorithm works
The Riegel equation is a model developed by Peter Riegel (1977) commonly used to predict running performance. Formula: T₂ = T₁ × (D₂ / D₁)^1.06, where T = time and D = distance. The exponent 1.06 represents progressive fatigue: doubling distance does not double time linearly.
Examples
You ran a 10km in 45 minutes and want to estimate your marathon time:
- 📊 T₁ = 45min (2700 seconds), D₁ = 10km
- 📊 D₂ = 42.195km (marathon)
- 📊 T₂ = 2700 × (42.195 / 10)^1.06 = 2700 × 4.49 = 12123 sec ≈ 3h22min
Your 10K pace (4:30/km) converts to an estimated marathon pace of 4:48/km. Note the degradation: +18 sec/km on marathon vs 10K.
Limits
The Riegel algorithm is an estimate, not a guarantee. Factors that affect accuracy:
- ⚠️ Specific endurance: Long-distance specialists may outperform the prediction
- ⚠️ Recent training: A record older than ~6 months is less reliable
- ⚠️ Course profile: Significant elevation skews the calculation (model assumes flat terrain)
- ⚠️ Weather: Heat >25°C may require adding 5-10% to the predicted time
- ⚠️ Race experience: First-time marathoners often underperform relative to the estimate
Tips
- ✅ Use a recent record: Ideally within the last 3 months on a measured course
- ✅ Enter multiple distances: Averaging predictions produces a more reliable estimate
- ✅ Add 5-10% for your first marathon or difficult conditions
- ✅ Test the predicted pace in training over 15–20km before the race
- ✅ Be conservative: Aim slightly slower and surprise yourself positively
❓ Race prediction FAQ
Is the Riegel predictor reliable?
Reliability ~85-95% for regularly trained runners. The algorithm is scientifically supported. It's most accurate with a recent record (<3 months), flat course, good weather and specific training for the target distance. It's less reliable for extremes (ultra distances, sprints <1km) or beginners.
Why is my predicted marathon time slower than 2× half-marathon?
This is normal and scientifically expected. A marathon is not 2× a half marathon due to glycogen depletion after ~30km, cumulative muscle fatigue and progressive dehydration. Empirically, marathon time ≈ half time × 2.1–2.2.
Which reference distance should I use to predict a marathon?
The half marathon is the best predictor (similar distance and endurance). A recent 10K also works if it was run at maximal effort. Avoid 5K (too short). Ideally: enter both a half and a 10K and average the predictions.
How can I improve my predicted time?
Improve your reference records! Gaining 1 minute on a 10K ≈ 4–5 minutes on marathon. Training plan: weekly long run (25–32km), tempo sessions (15–20km), VO2 max intervals (400m). Attempt a new record 4–6 weeks before your target race and recalculate.