How to use it
Enter the distance and finish time of one recent race — the fresher and harder the effort, the better the prediction. The calculator instantly returns predicted finish times for the mile, 5K, 10K, half marathon and marathon, using two independent models so you see a realistic range instead of a single number.
Tap Go advanced to pick a target race and see even-paced splits for your predicted time. Then carry that goal pace into the Pace Calculator to plan negative or positive splits.
Riegel vs VDOT
The Riegel formula, T2 = T1 × (D2/D1)1.06, is quick and works well between roughly half and double your input distance. It tends to be optimistic for big jumps — a marathon predicted from a 5K, for example.
The VDOT model from Jack Daniels and Jimmy Gilbert estimates the oxygen cost of your pace and how long you can hold a share of your maximum, which usually makes it steadier across large distance gaps. Where the two disagree, the truth is often in between.
Getting a reliable prediction
Predictions assume you've trained for the target distance. A short race says what you're capable of aerobically, but a marathon still demands long-run endurance the formula can't see. Use the number as a target to train toward, not a guarantee.
What VDOT means
VDOT is a single number that captures your current running fitness from a race result. A higher VDOT means a faster runner. It's handy for comparing efforts across distances: a 20:00 5K and a 41:30 10K are almost the same VDOT, so either can seed your predictions.
| VDOT | 5K | Marathon |
|---|---|---|
| 40 | 22:30 | 3:49 |
| 50 | 19:57 | 3:10 |
| 60 | 17:03 | 2:43 |
Approximate equivalents — your predictions are computed live from your own race.
Predict, then pace
A predictor sets the goal; a pace plan gets you there. Once you have a target time, our Pace Calculator turns it into per-kilometre or per-mile splits with even, negative or positive strategies.
Train by heart rate?
Pair your goal pace with the right effort using the Heart Rate Zone Calculator to find your easy Zone 2 and threshold ranges.
Common questions
How does a race time predictor work?
It takes the distance and time of one recent race and estimates your finish time at other distances. This calculator runs two models at once — Riegel, a simple endurance formula, and VDOT, the Daniels & Gilbert oxygen-cost model — so you see a realistic range rather than a single guess.
What is the Riegel formula?
Peter Riegel's formula predicts a new time as T2 = T1 × (D2/D1)1.06. The 1.06 exponent captures how pace slows as distance grows. It's accurate roughly between half and double your input distance and tends to be optimistic for very long extrapolations.
What is VDOT?
VDOT is a running fitness score from Jack Daniels and Jimmy Gilbert. It estimates the oxygen cost of your race pace and how long you can hold a percentage of your maximum, then converts that into equivalent times at other distances. It usually handles big distance jumps better than Riegel.
Which prediction should I trust?
Predictions are most reliable when the target is close to the race you entered and you've built the endurance for it. For a marathon predicted from a short race, treat the number as a ceiling that assumes proper long-run training. When in doubt, aim between the two models.