Race time predictor
What a result at one distance suggests you can run at another. Every figure below comes from the Riegel formula, the same calculation the interactive predictor uses.
How the prediction works
Riegel's formula scales a known result by the ratio of the two distances, raised to a power:
predicted time = known time x (new distance / known distance) ^ 1.06
The exponent is the whole idea. At 1.0 you would hold the same pace forever, which nobody does. At 1.06 the formula models the slowing down that comes with distance. Some coaches use 1.07 or 1.08 for the marathon specifically, which is more conservative and often more accurate for anyone who has not built marathon specific endurance.
The tables below use 1.06. Treat them as an upper bound on what your current fitness allows, not a target to train toward.
If you have run a 5K
| 5K time | 10K | Half Marathon | Marathon |
|---|---|---|---|
| 20:00 | 41:42 | 1:32:00 | 3:11:49 |
| 22:00 | 45:52 | 1:41:12 | 3:31:00 |
| 25:00 | 52:07 | 1:55:00 | 3:59:47 |
| 28:00 | 58:23 | 2:08:48 | 4:28:33 |
| 30:00 | 1:02:33 | 2:18:00 | 4:47:44 |
| 35:00 | 1:12:58 | 2:41:00 | 5:35:41 |
If you have run a 10K
| 10K time | 5K | Half Marathon | Marathon |
|---|---|---|---|
| 40:00 | 19:11 | 1:28:15 | 3:04:00 |
| 45:00 | 21:35 | 1:39:17 | 3:27:01 |
| 50:00 | 23:59 | 1:50:19 | 3:50:01 |
| 55:00 | 26:23 | 2:01:21 | 4:13:01 |
| 1:00:00 | 28:47 | 2:12:23 | 4:36:01 |
| 1:10:00 | 33:34 | 2:34:27 | 5:22:01 |
If you have run a Half Marathon
| Half Marathon time | 5K | 10K | Marathon |
|---|---|---|---|
| 1:30:00 | 19:34 | 40:47 | 3:07:39 |
| 1:40:00 | 21:44 | 45:19 | 3:28:30 |
| 1:45:00 | 22:50 | 47:35 | 3:38:55 |
| 1:50:00 | 23:55 | 49:51 | 3:49:21 |
| 2:00:00 | 26:05 | 54:23 | 4:10:12 |
| 2:15:00 | 29:21 | 1:01:11 | 4:41:28 |
| 2:30:00 | 32:36 | 1:07:59 | 5:12:44 |
If you have run a Marathon
| Marathon time | 5K | 10K | Half Marathon |
|---|---|---|---|
| 3:00:00 | 18:46 | 39:08 | 1:26:20 |
| 3:30:00 | 21:54 | 45:39 | 1:40:43 |
| 4:00:00 | 25:01 | 52:10 | 1:55:07 |
| 4:30:00 | 28:09 | 58:42 | 2:09:30 |
| 5:00:00 | 31:17 | 1:05:13 | 2:23:53 |
Where predictions go wrong
Riegel assumes you are equally well trained for both distances. Almost nobody is. The formula is at its most reliable between neighbouring distances, and at its least reliable predicting a marathon from a 5K, where it quietly assumes an endurance base that a fast 5K says nothing about.
It also assumes even effort on a flat course in good conditions. Heat, hills and a congested start all cost time no formula accounts for.
Turn a prediction into a pacing plan
Once you have a target, the calculator gives you the pace it needs and the split times to run it.