Race Time Predictor
By Miikka · CalcBrew · Updated
52.1 min
Predicted time
| Predicted time | 52.1 min |
| Target pace | 5.21 min/km |
The race time predictor estimates your time for a new distance based on a previous running result. It applies Riegel's formula and also tells you the pace you should aim for over the target distance.
How the calculator works and what it’s for▾
How the prediction works
The calculator uses Riegel's formula t2 = t1 × (d2/d1)^1.06, scaling your known time and distance to the target distance. The 1.06 exponent accounts for the fact that pace slows as distance grows.
For example, if you run 5 km in 25 minutes, the formula predicts a little over 51 minutes for 10 km.
What you enter and what you get
Enter your known distance, the time you ran it in, and your target distance. The result is your predicted finishing time and the target pace in minutes per kilometre.
The target pace helps you hold a steady rhythm in a race or on a long training run.
Who it is for
It serves recreational runners and anyone preparing for a race who wants a realistic time goal for a new distance. You can set a target for, say, your first half marathon based on a recent 10 km time.
It is also handy for choosing a pace group at a large running event.
Interpretation and limits
The prediction is most accurate for similar distances at the same fitness level. The larger the jump in distance, the less certain the result.
The formula assumes adequate endurance training. If your endurance is not yet built for the longer distance, your real time may be slower than predicted.
🔄 Reviewed June 2026
Frequently asked questions
Cite this calculator
CalcBrew. (2026). Race Time Predictor. https://calcbrew.com/race-time-predictor“Race Time Predictor.” CalcBrew, 2026, calcbrew.com/race-time-predictor.Link to https://calcbrew.com/race-time-predictor. Results are estimates; cite the underlying formula or data source for academic work.
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