Marathon Time Predictor
Use this marathon time predictor to estimate your marathon finish time from a recent race or hard training effort. It provides a simple way to turn a known performance over one distance into a projected time over another.
Recent Race Distance
Time
Predicted Marathon Time: --
How the Marathon Predictor Works
The marathon time predictor uses your result from a recent race - typically a half marathon, 10K, or parkrun - to estimate what you should be capable of over the full marathon distance. The calculation is based on Riegel's endurance formula, which models the relationship between race distance and finishing time across a population of trained runners.
How Accurate Is It?
The prediction is a useful guide, not a guarantee. It assumes that your training for the marathon has been specific and appropriate for the distance - primarily that you have built sufficient aerobic base and long run capacity. If your target race is a half marathon but your longest recent run is 10 kilometres, the prediction will be optimistic.
The formula also does not account for race conditions, course profile, temperature, or how well you execute your pacing and fuelling strategy on the day. A conservative, well-executed race will often outperform the prediction. A fast start followed by a difficult second half will often underperform it.
Using the Prediction to Set Race Pace
Once you have a predicted finish time, divide it by 42.2 to get your target pace per kilometre. Build your race strategy around that pace - ideally aiming for an even split or a very slight negative split (running the second half marginally faster than the first). Consistency of effort is more important than hitting an exact number at each kilometre marker.
What About the First Marathon?
For athletes running their first marathon, the prediction should be treated with additional caution. The physical and psychological demands of the final 10 kilometres are difficult to prepare for fully in training. Running conservatively through the first half - even if it feels easy - is almost always the right strategy.
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