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Race Time Predictor

Predict finish times at other distances from one recent race, using Riegel’s formula.

Enter values

Results update as you type.

Result

Predicted marathon

3:40:48.6

Riegel’s formula assumes consistent training; marathon predictions need endurance training to hold true.

Predicted half marathon
1:45:54.4
Predicted 10K
0:48:00
Predicted 5K
0:23:01.3

Equivalent performances

RaceTimePace / km
1 km0:04:10.84:10.8
1 mile0:06:55.44:18.1
5 km0:23:01.34:36.3
10 km0:48:004:48
Half marathon1:45:54.45:01.2
Marathon3:40:48.65:14

About the Race Time Predictor

Predict finish times at other distances from one recent race, using Riegel’s formula.

Also known as: race predictor, riegel formula, equivalent race times, predict marathon time.

How to use this calculator

  1. Enter recent race distance, distance unit, time (h:mm:ss).
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

T₂ = T₁ × (D₂ / D₁)^1.06

Worked example

Using the values pre-filled in the calculator above:

  • Recent race distance = 10
  • Distance unit: Kilometres
  • Time (h:mm:ss): 00:48:00

the calculator returns:

  • Predicted marathon: 3:40:48.6
  • Predicted half marathon: 1:45:54.4
  • Predicted 10K: 0:48:00
  • Predicted 5K: 0:23:01.3