Running Race Predictor
Predict your next race time
Use a recent race result to estimate your likely pace and finish time across other distances.
5 km, 10 km, half marathon, and more.
Results shown in kilometres and miles.
This works best when your reference race is similar to your target race.
Similar weather. Similar terrain. Clean race flow.
Understanding how one performance carries across distances helps you set realistic goals and pace your training with more confidence.
How to use the calculator
- Enter a recent race result.
- Choose a target distance or add your own.
- Click Predict.
Use the results as a guide, not a promise.
Fitness, terrain, weather, and your race execution all matter.
Recent Run Details
Upcoming Run
Predicted finish time
Predicted pace /km
Predicted pace /mi
Turn this prediction into a plan.
Get Coached and train with clear structure and real guidance that fits your life.
A few things worth knowing...
How accurate is this prediction?
It’s
an estimate, not a promise. The Riegel Formula assumes similar fitness
and conditions between races. Well-trained runners often find it
accurate within a few percent for distances up to a marathon.
Longer or trail races tend to show larger deviations.
What is the Riegel Formula?
The model by Peter Riegel expresses how race time increases with distance:
T₂ = T₁ × (D₂ / D₁) ^ 1.06
where 1.06 is the fatigue factor used for most runners.
A lower number favours endurance athletes; higher values fit speed-oriented runners.
Why don’t I see an “effort” or “fatigue” input?
To keep things simple, this version fixes the fatigue factor at 1.06, which works well for most runners. You can assume the calculator already applies it under the hood.
How do I use the predicted pace?
The output shows pace in both km and miles.
Use these paces during your race pace sessions. Cross-check them against perceived effort and heart rate.
In the final weeks, dial things in and settle on a pace you believe you can hold for the full race.
What does this calculator not account for?
This calculator assumes consistent training and similar conditions.
It does not account for weather, terrain, course profile, or race day factors like congestion and pacing errors.
Use it as a guide, not a guarantee.
The closer your past race and future race are in conditions and execution, the more useful the prediction will be.
Muscular conditioning also matters, especially as race distance increases.
Make sure your training prepares your muscles to handle the demands of the longer distance.