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Race Time Predictor
Predict your 5K, 10K, half marathon or marathon finish time from a recent race. Six models, most based on published research, one honest number with a confidence range.
How the race time calculator works
Most predictors use a single formula and walk away. PaceBrain runs six models, most based on published research, weighted by how recent and how similar in distance your races are, and shows the range instead of a false-precision number.
Critical Velocity
Adapted from the Jones & Vanhatalo (2017) hyperbolic model. With one recent race, PaceBrain estimates how long a pace can be held.
Endurance Index
Adapted from Billat et al. (1999). PaceBrain scales a race by a distance-band fraction of vVO2max.
Power Law
Katz & Katz (1999) describe how pace decays as the race gets longer. PaceBrain uses that published form.
VDOT (Daniels)
Jack Daniels' distance-equivalence tables convert one race result into an expected time at another distance.
Riegel formula
Adapted from Riegel (1981). PaceBrain scales time with distance using a fatigue factor for the change in distance, not an exponent taken from your training.
Pace-decay curve
Our own curve for how pace slows over longer distances.
Want the detail on accuracy? How accurate are race time predictors? An honest look at the research.
Predict any distance, 5K to marathon
5K time predictor
Enter a recent parkrun or track 5K and see your projected 5K, plus what it implies for longer races.
10K time predictor
A 10K is a great predictor race. We translate it into an accurate 10K goal and half marathon estimate.
Half marathon predictor
Predict your half marathon finish time from a 5K, 10K or a recent long run and training volume.
Marathon time predictor
Marathons punish over-optimistic goals. We factor in your long run and mileage, not just raw speed.
Honest ranges
We show a confidence band, not a single number you'll be tempted to over-trust.
Instant & free
Your first estimate in about 30 seconds, with no account required.
Built to improve you
Save a prediction and PaceBrain builds a plan to close the gap to your goal.
Frequently asked questions
How does a race time predictor work?
It takes a recent race result and converts it into an expected time at your goal distance using endurance models such as VDOT (Daniels), the Riegel formula and our own pace-decay curve. PaceBrain combines six models, most based on published research, weighted by how recent and how similar in distance your races are, rather than relying on a single equation.
How accurate are race time predictors?
We combine several models and factor in training load. We always show a confidence range instead of one false-precision number, including when the goal race is much longer than the one you entered.
Can I predict my marathon time from a 5K or 10K?
Yes, but treat it as a ceiling. A 5K or 10K reflects your speed; the marathon also depends on endurance, fuelling and your long-run history. Our marathon estimate factors in weekly mileage and longest recent run so it is not just a raw pace conversion.
Do I need to sign up to use the race time calculator?
No. The predictor is free and needs no account. Create a free PaceBrain account only if you want to save your prediction and get a training plan built to close the gap to your goal.
What information do I need to get a prediction?
At minimum, one recent race time and distance. Adding your age, weekly mileage, longest run and, optionally, VO₂ max makes the estimate more accurate.
Related reading: Strength training for runners · VO₂ max for runners · Free marathon training plan
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