Race Time Predictor

Enter a recent race time to predict your equivalent finish times across all major distances. Powered by the scientifically-validated Riegel formula used by coaches worldwide.

Race Time Predictor

Enter a recent race result to predict equivalent times at other distances.

Distance

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How the Race Time Predictor Works

This tool uses the Riegel formula, a scientifically validated method for predicting equivalent race performances across different distances. The formula is:

T₂ = T₁ × (D₂ / D₁)^1.06

Where T₁ is your known time at distance D₁, and T₂ is the predicted time at distance D₂. The exponent 1.06 accounts for the fatigue factor — as distance increases, pace naturally slows.

Why This Formula Works

The Riegel model was developed by Dr. Peter Riegel in 1981 and has been validated against thousands of race results. It assumes that runners maintain a consistent fraction of their aerobic capacity across distances. The 1.06 exponent reflects the physiological reality that longer races require more glycogen utilization and mental endurance.

Tips for Accurate Predictions

• Use a race result from the last 3-6 months at maximum effort
• Choose input distances close to your target distance
• Ensure similar race conditions (weather, terrain, altitude)
• Factor in training volume — more miles = more accurate predictions
• Account for tapering — tapered races predict better than training runs

Example Predictions

If you run a 5K in 25:00:

• 10K prediction: 52:00 (pace: 8:23/mi)
• Half Marathon prediction: 1:56:00 (pace: 8:51/mi)
• Marathon prediction: 4:03:00 (pace: 9:16/mi)

Frequently Asked Questions

How accurate is the Riegel formula for race prediction?

The Riegel formula is accurate within 3-5% for most runners when predicting times within 2x the input distance. For example, predicting a half marathon from a 10K time is highly accurate. Predicting a marathon from a 5K is less precise due to the endurance factor.

Can I predict a marathon time from a 5K result?

Yes, but with less accuracy. The formula works best when the target distance is within 2x the input distance. For marathon prediction, a half marathon or 10K result will give more accurate predictions.

What is a good marathon time for a beginner?

For most beginner runners, finishing a marathon in 4:30:00 to 5:00:00 is a solid goal. The average marathon time is approximately 4:30:00 for men and 4:50:00 for women. Focus on finishing rather than time for your first marathon.

How do I improve my race time prediction accuracy?

Use a recent race result from the last 3-6 months at maximum effort. The closer the input distance to your target distance, the more accurate the prediction. Ensure the race conditions (weather, terrain, altitude) are similar.

What is the difference between Riegel and other race prediction formulas?

The Riegel formula uses a fatigue exponent of 1.06, which works well for distances from 5K to marathon. Other formulas like Daniels or Pfitzinger use different exponents and may be more accurate for specific distances or runner types.

Race Time Predictor