Race Time Predictor
Enter a recent race result and see what it predicts for every other distance.
Predictions assume equal training for each distance, a flat course and good conditions.
5K time equivalents
What common 5K times predict for longer races (Riegel, exponent 1.06).
| 5K | 10K | Half marathon | Marathon |
|---|---|---|---|
| 16:00 | 33:22 | 1:13:36 | 2:33:27 |
| 18:00 | 37:32 | 1:22:48 | 2:52:38 |
| 20:00 | 41:42 | 1:32:00 | 3:11:49 |
| 22:00 | 45:52 | 1:41:12 | 3:31:00 |
| 24:00 | 50:02 | 1:50:24 | 3:50:11 |
| 25:00 | 52:07 | 1:55:00 | 3:59:47 |
| 27:00 | 56:18 | 2:04:12 | 4:18:58 |
| 30:00 | 1:02:33 | 2:18:00 | 4:47:44 |
| 33:00 | 1:08:48 | 2:31:48 | 5:16:30 |
| 36:00 | 1:15:03 | 2:45:36 | 5:45:17 |
| 40:00 | 1:23:24 | 3:04:00 | 6:23:39 |
How it works
Riegel’s formula scales your time by distance with a fatigue exponent (1.06 for most runners). VDOT, from Jack Daniels’ Running Formula, estimates the oxygen cost of your race pace and how long you can sustain it, then finds the time that gives the same effective VO2 max at each distance. All calculations happen in your browser.
How accurate are race time predictions?
For distances close to your input race they are usually within 1–3%. Predicting a marathon from a 5K is less reliable: the marathon also depends on long-run volume, fuelling and pacing, so most runners are a few minutes slower than the prediction unless they have trained specifically for the distance.
Riegel or VDOT — which should I trust?
Both agree closely for 5K to half marathon. Riegel (T2 = T1 × (D2/D1)^1.06) is a simple fatigue curve; Jack Daniels’ VDOT models oxygen cost and how long you can hold a given share of VO2 max. Use the slower of the two for marathon planning.
What is VDOT?
VDOT is Jack Daniels’ performance index: an effective VO2 max derived from a race result. The higher the VDOT, the faster your equivalent times at every distance. It is also the basis for his training paces.
Which race should I enter?
Use a recent, all-out race or time trial on a flat course. Training runs underestimate your ability, and races longer than about two hours are affected by fuelling more than fitness.