Race Finish-Time Predictor

Predict 10K, half and marathon times from a recent race. Free, private and instant.

How to use the Race Time Predictor

  1. Choose recent race distance: 1 mile, 3 km, 5 km, 10 km and more.
  2. Enter your finish time in hours, minutes and seconds.
  3. Choose predict time for: 1 mile, 3 km, 5 km, 10 km and more.
  4. Choose endurance: Well trained (exponent 1.06), Average mileage (1.07) or Low mileage (1.08).
  5. Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.

About the Race Time Predictor

Use a recent race result to predict your finish time at other distances with the Riegel formula, and see how pace slows as distance grows. Pick your training level to adjust the fatigue exponent.

Also known as: race time predictor, marathon time predictor, Riegel calculator, half marathon predictor, 10K time predictor.

Worked example

Predicted Half marathon (21.1 km) time: 1:55:00 (5:27 /km). Based on 25:00 for 5 km, you could run Half marathon (21.1 km) in about 1:55:00 (5:27 /km).

Formula and cut-offs

Riegel: T2 = T1 x (D2 / D1)^k, where k = 1.06 for well-trained, 1.07 for average and 1.08 for low mileage runners.

Frequently asked questions

How accurate is the Riegel formula?

It is a good guide for 5K to half marathon, but marathons need long-run training to match it.

What exponent should I use?

1.06 is standard; use 1.07 or 1.08 if you run low weekly mileage.

Should I use a recent race?

Yes, within the last 4 to 8 weeks and at full effort.

Sources and references

Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.

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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.