Enter one recent race. See what it predicts for every distance from 5K to the marathon, the pace each one needs, and the threshold pace your training should be built on. The math is the same the Endurance by Design app uses to set your paces.
| Distance | Predicted time | Pace / mi | Pace / km |
|---|
Endurance by Design turns this goal into a periodized plan with these paces on every run card, and adapts it when life gets in the way. Free to download, 7-day free trial.
The predictor uses Riegel's formula, the standard way to translate one race result into another distance. Your time scales with the ratio of the distances raised to a power slightly above one, because pace slows as distance grows.
Predicted time = your time × (target distance ÷ your distance)1.06The exponent 1.06 is the one the Endurance by Design app uses to project any result to a one-hour effort, which is how it finds your threshold pace. Threshold pace is the anchor for the five training zones in the pace and zone calculator, so the number shown here is the number your plan would train on.
A half marathon in 1:45:00 is 4:59 per km, or 8:01 per mile. The formula predicts:
| Distance | Predicted time | Pace / mi | Pace / km |
|---|---|---|---|
| 5K | 22:50 | 7:21 | 4:34 |
| 10K | 47:35 | 7:40 | 4:46 |
| Half marathon (entered) | 1:45:00 | 8:01 | 4:59 |
| Marathon | 3:38:55 | 8:21 | 5:11 |
The same 1:45 half projects a one-hour effort of 4:49 per km (7:46 per mile). That is this runner's threshold pace, and marathon pace of 5:11 sits where it should, in the tempo zone just below it.
Updated October 21, 2026
Within a few percent when the two distances are close and you have trained for both. The prediction assumes equal preparation for the target distance. A 5K result predicts a marathon optimistically unless your long runs and weekly volume match marathon training.
Riegel's formula: predicted time equals your time multiplied by the ratio of the distances raised to the power 1.06. It is the same exponent the Endurance by Design app uses to project a result to a one-hour effort for threshold pace.
Threshold pace is the pace you could hold for about an hour. Training zones for easy, aerobic, tempo, threshold and interval running are set as multiples of it, so it is the one number a plan needs from your result.
The most recent all-out effort from the last two or three months, ideally the distance closest to your goal. A time trial counts. Avoid a race you ran as a workout or in bad conditions.
Yes. Enter the goal as if it were a result and the table shows what you would need to be running at the shorter distances. If your current 10K is well off that line, the goal needs more time.
No. It is a pure fitness projection. Heat, elevation and terrain add time on top of it, and the shorter the race you enter, the more the marathon prediction depends on endurance you still have to build.
Tell Endurance by Design your race and your week, and it builds a periodized plan backward from race day with your paces on every session. Free to download on the App Store, with a 7-day free trial.
