Race Time Predictor

Estimate an equivalent running time at another distance using a known performance

Uses the Riegel 1.06 exponent. Treat the result as a performance estimate, not a guaranteed finish time.

Your result will appear here.

About the Race Time Predictor

Race Time Predictor estimates a likely time at one running distance from a known performance at another distance. It is useful for setting broad training or pacing targets when the athlete has a recent race result.

Prediction formulas assume endurance changes in a typical way as distance increases. Training specificity, terrain, weather and the gap between distances can make an individual result meaningfully faster or slower than the estimate.

How to Use the Race Time Predictor

  1. Enter a recent race distance.
  2. Enter the corresponding finish time.
  3. Choose the target race distance.
  4. Calculate the predicted time and use it as a planning range rather than a guaranteed performance.

How the Calculation Works

A common model is the Riegel formula: T₂ = T₁×(D₂/D₁)^k, where T is time, D is distance and k is an endurance exponent often near 1.06 for general running predictions.

The exponent makes predicted time increase slightly faster than distance because sustainable pace usually slows as race distance becomes longer.

Worked example

Race Time Predictor Worked Example

25-minute 5K predicting a 10K with k=1.06

T₂ = 25×(10/5)^1.06 = 25×2^1.06 ≈ 52.1 minutes.

Result guide

Understanding Your Race Time Predictor Result

The estimate assumes fitness is reasonably developed for both distances. A runner trained specifically for 5K speed may underperform the formula at a half marathon without sufficient endurance preparation.

Before you rely on the answer

Assumptions and Limitations

  • The known performance is recent and representative.
  • Target and known races are comparable enough for the model.
  • The selected endurance exponent is treated as an estimate rather than a personal constant.

Practical tip

Using This Result in Practice

Use a race predictor to set an initial target, then adjust it with recent long runs, course profile and conditions. Predictions become less reliable when extrapolating from a very short race to a much longer one.

Related calculations

Useful Calculations to Continue With

Once you have a target time, use the Running Split Calculator to turn it into checkpoint times.

If you want the predicted effort expressed in another pace unit, use the Pace Converter.

Common questions

Race Time Predictor FAQ

How does a race-time predictor work?

It scales a known performance to another distance using a model of how pace typically slows as distance increases.

Is the predicted time guaranteed?

No. Training, course, weather and individual endurance can change actual performance.

Why are longer-race predictions slower than simply doubling time?

Most runners cannot sustain the same pace as distance increases, so the model includes an endurance penalty.