Running
Marathon Time Predictor
Estimate your marathon finish from a recent shorter race with the Riegel model, including the halfway split.
Free · instant · no sign-upDeterministic
Result
Predicted marathon3:38:55
Even effort, comparable conditions.
Marathon pace5:11/ km
Halfway split1:49:28at 21.1 km
Riegel prediction — training volume and fuelling strongly affect real marathon time.
The formula
Riegel's formula (to 42.195 km)
T_marathon = T₁ × (42.195 ÷ D₁)^1.06
Source: Peter Riegel (1981)
What it means
- A realistic starting estimate for goal marathon pace.
- Comes with the halfway split so you can plan an even race.
Limitations
- Marathon performance depends heavily on long-run volume and fuelling, which no formula sees.
- Predicting from a 5 k overestimates for under-trained runners.
Educational only
This is a deterministic tool: the same inputs always give the same result. It is for learning and planning, not a substitute for coaching or measurement.
Keep exploring
Follow the threads from this tool into the wider knowledge base.