Marathon Time Predictor
Predict your marathon time from a recent race result.
Your finishing time for that race, in minutes.
42.195 km for a full marathon.
Results update as you type.
How it works
This marathon time predictor estimates how long a marathon, or any target distance, might take you based on a race you have recently completed. It applies the Riegel formula: enter the distance and time of a recent result and the distance you are aiming at, and it projects a finishing time. Times are handled in minutes so the numbers stay easy to read and enter. Predicting a marathon time matters because pacing a 42.195-kilometre race well is difficult, and starting too fast is the classic mistake that leads to hitting the wall. A grounded prediction from a recent half-marathon or 10K gives you a target pace to rehearse in training and to hold on race day. Coaches use it to set goal paces, and runners use it to choose a realistic finish-time ambition rather than an arbitrary round number. The formula works because running pace slows in a predictable way as distance increases, and the exponent 1.06 captures that fade accurately across common racing distances. The prediction assumes you have trained appropriately for the longer event, so it is most reliable when your recent race is reasonably close in distance and your endurance base supports the marathon. Treat the output as an informed goal to train toward, not a guarantee, since fuelling, heat, and course profile all shape the real result.
T2 = T1 × (D2 ÷ D1)^1.06
The Riegel model projects a finishing time by scaling a known race to a new distance and raising the distance ratio to the power 1.06. That exponent, a little above one, encodes the fact that pace fades as distance grows, since nobody can hold a short race's speed over a marathon. Multiplying your recent time by this factor stretches it in proportion to how much longer the target race is, giving a realistic prediction rather than a naive linear scale-up.
Source:Riegel model (race prediction)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter recent race distance, recent race time and target distance.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Predicted time updates instantly as you type — no button to press.
Frequently asked questions
What is the Riegel formula?
The Riegel formula, published by Peter Riegel, predicts race times across distances by multiplying a known time by the distance ratio raised to the power 1.06. The exponent reflects that runners slow slightly as races lengthen. It is trusted because it is simple and matches real results well from about 1,500 metres up to the marathon, making it a standard tool for setting realistic goal paces from a recent performance.
Which recent race should I use as input?
Use a recent, well-paced race at a distance not too far from your target for the most reliable prediction. A half-marathon is an excellent basis for a marathon estimate because the endurance demands overlap closely. A short 5K can also work but tends to produce an optimistic marathon time, since it assumes endurance you may not yet have. Pick a result that genuinely reflects your current fitness rather than a personal best from months ago.
Why enter time in minutes?
The calculator works in minutes to keep entry and output simple and consistent. Convert your finishing time first by multiplying hours by sixty and adding the remaining minutes and any fractional seconds. A half-marathon of one hour forty minutes becomes 100 minutes. The predicted time is also returned in minutes, which you can convert back into hours and minutes to plan a familiar marathon goal pace and split strategy.
How accurate is a marathon prediction?
Predictions are most accurate when your input race is close in distance and you have completed marathon-specific endurance training. Jumping from a 5K straight to a marathon estimate assumes stamina you may lack, so the projection can be too fast. The marathon is also uniquely exposed to fuelling and the wall, which no formula models. Use it as a target to train toward, and expect heat, hills, and pacing to move the real time.
Can I predict shorter races too?
Yes. The formula works in both directions, so you can project down from a marathon to a half-marathon or 10K as well as up. Predicting a shorter, faster race from a longer result usually gives a slightly conservative target, because your speed over short distances may beat what an endurance-based formula assumes. Either way, base the prediction on a recent race that reflects your present fitness for the most useful result.