Predicted Marathon Times from 10K Results
| 10K Time | Predicted Marathon | Target Pace/km |
|---|---|---|
| 35:00 (3:30/km) | 2:40:22 | 3:48/km |
| 37:30 (3:45/km) | 2:51:44 | 4:04/km |
| 40:00 (4:00/km) | 3:03:17 | 4:20/km |
| 42:30 (4:15/km) | 3:14:50 | 4:37/km |
| 45:00 (4:30/km) | 3:26:12 | 4:53/km |
| 47:30 (4:45/km) | 3:37:45 | 5:09/km |
| 50:00 (5:00/km) | 3:49:07 | 5:25/km |
| 55:00 (5:30/km) | 4:12:02 | 5:58/km |
| 60:00 (6:00/km) | 4:34:57 | 6:30/km |
Predicted Marathon Times from Half Marathon Results
| Half Marathon Time | Predicted Marathon | Multiplier Used |
|---|---|---|
| 1:30:00 | 3:06:59 | 2.08× |
| 1:40:00 | 3:27:45 | 2.08× |
| 1:45:00 | 3:37:58 | 2.08× |
| 1:50:00 | 3:48:11 | 2.08× |
| 2:00:00 | 4:08:37 | 2.08× |
| 2:15:00 | 4:39:44 | 2.08× |
| 2:30:00 | 5:10:50 | 2.08× |
How the Riegel Formula Works
The Riegel formula is: T₂ = T₁ × (D₂/D₁)^1.06
T₁ = your known race time, D₁ = known race distance, D₂ = target distance, T₂ = predicted time. The exponent 1.06 captures the physiological fatigue factor — longer races require proportionally more energy, so your pace naturally slows.
The Riegel formula was first published by Pete Riegel in Runner's World in 1977. It remains the most widely used prediction model in recreational running.
How Accurate is Marathon Prediction?
For trained runners with marathon-specific preparation, Riegel predictions are typically within 2–5% of actual finish times. Recreational runners doing their first marathon often run 5–15% slower than predicted from shorter race times. Reasons include inadequate long run training, nutrition issues, and the unique physical demands of running beyond 30km.
Frequently Asked Questions
How do I predict my marathon time from a 10K?
Use the Riegel formula: multiply your 10K time by approximately 4.66. A 45-minute 10K predicts a 3:26 marathon. Use the Race Predictor tool on this site for exact calculations.
How do I predict my marathon time from a half marathon?
Multiply your half marathon time by approximately 2.09 using the Riegel formula. A 1:45 half marathon predicts approximately a 3:38 marathon.
Why is marathon prediction often optimistic?
The Riegel formula assumes proportional training. Many runners who run fast 10Ks or half marathons have not done the long runs (32km+) required to build the glycogen capacity and muscular resilience for the marathon. The last 10km of a marathon has no equivalent in shorter races.
Can I predict a marathon from a 5K time?
Yes, but accuracy decreases as the distance gap widens. A 10K or half marathon gives a more reliable marathon prediction because the physiological demands overlap more closely.