Estimate a marathon from one shorter race, derive a personal exponent from two races, or work backward from a marathon goal.
How the Marathon Time Predictor Works
This page fixes the target at 42,195 meters and uses shorter-race performance to estimate marathon time. It adds marathon pace, exponent scenarios, and even-pace checkpoints.
One-race mode uses a selected fatigue exponent. Two-race mode derives a personal exponent, while reverse mode finds the shorter-race time associated with a marathon goal.
Formula and Method
Formula: Tmarathon = Tsource x (42195 / Dsource)^k
The expandable scenario table recalculates at k values of 1.06, 1.08, and 1.10. Two-race mode uses k = ln(T2/T1) / ln(D2/D1). In reverse mode, scenarios reuse the source time implied by the entered marathon goal and selected exponent.
Choosing the Right Inputs
Use a recent race shorter than the marathon and representative of current fitness. Two-race inputs should be comparable all-out efforts.
| Exponent | Projection effect | Use |
|---|---|---|
| 1.06 | Fastest scenario | Classic Riegel starting point |
| 1.08 | More fatigue | Sensitivity check |
| 1.10 | Most fatigue of these rows | Conservative sensitivity check |
Understanding Your Results
The predicted finish (or model-implied source time in reverse mode) leads, followed by pace. Expand Calculation details for three exponent scenarios and even-pace checkpoints through the finish.
Scenario spread is more honest than presenting one exact-looking answer. A personal exponent is still a projection, not a race-day guarantee.
Worked Example
A 1:45 half marathon at k = 1.06 predicts about 3:38:55. A 45:00 10K predicts about 3:27:01.
Common Mistakes
Do not mix training-run and race-effort results, use a source distance at or above the marathon, or confuse even-pace checkpoints with a pacing prescription.
Assumptions and Limitations
Research in recreational runners shows a fixed Riegel formula can underestimate marathon time. The tool does not model preparation, fueling, terrain, temperature, wind, or race execution.
Sources
Peter S. Riegel. Athletic Records and Human Endurance. American Scientist, 1981.
Andrew J. Vickers and Emily A. Vertosick. An Empirical Study of Race Times in Recreational Endurance Runners. BMC Sports Science, Medicine and Rehabilitation, 2016.
