Predicted race times
5K
9:01 /mi
28:00
10K
9:24 /mi
58:23
Half marathon
9:50 /mi
2:08:48
Marathon
10:15 /mi
4:28:33
How it works
The predictor uses Riegel's formula, T2 = T1 × (D2 ÷ D1)^1.06. It takes your time over one distance and scales it to another, slowing your pace slightly as the distance grows. The 1.06 reflects how much most runners slow down as races get longer: double the distance takes about 4 percent more than double the time.
Getting a useful prediction
- Use a race or an all-out time trial from the last couple of months, not an easy run.
- Predict distances close to the one you ran. A 10K predicts a half marathon better than a 5K does.
- Treat longer predictions as what's possible with the right training, not a promise.
Equivalent race times
Each row shows race times of roughly equal difficulty.
| 5K | 10K | Half marathon | Marathon |
|---|---|---|---|
| 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 |
| 26:00 | 54:12 | 1:59:36 | 4:09:22 |
| 28:00 | 58:23 | 2:08:48 | 4:28:33 |
| 30:00 | 1:02:33 | 2:18:00 | 4:47:44 |
| 32:00 | 1:06:43 | 2:27:12 | 5:06:55 |
| 34:00 | 1:10:53 | 2:36:24 | 5:26:06 |
| 36:00 | 1:15:03 | 2:45:36 | 5:45:17 |
| 38:00 | 1:19:14 | 2:54:48 | 6:04:28 |
| 40:00 | 1:23:24 | 3:04:00 | 6:23:39 |
Turn a prediction into training
A goal time only helps if your training matches it. Get your paces from the training pace calculator, then follow a half marathon or marathon training plan.
Common questions
- How accurate is a race time predictor?
- It's a good estimate when the two distances are close and you've trained for the longer one. Predicting a marathon from a 5K is the least reliable, because most runners haven't done the long runs a marathon needs.
- What formula does this race predictor use?
- Riegel's formula: T2 = T1 × (D2 ÷ D1)^1.06, where T1 is your time over distance D1 and T2 is the predicted time over distance D2. Engineer Pete Riegel published it in 1977.
- Can I predict my marathon time from a half marathon?
- Yes. Riegel's formula works out to roughly double your half marathon time plus 4 to 5 percent. A 2:00 half suggests about a 4:10 marathon, if you've done the marathon training.
- Why was my race slower than the prediction?
- Heat, hills, pacing, fueling and training all matter. The prediction assumes a flat course, good conditions and training suited to the distance.