Cameron Race Time Prediction Calculator
Cameron's formula predicts a finish time at a new race distance from a result you already have. Rather than a single fixed slowdown exponent, it uses a fatigue factor that varies smoothly with distance, which tends to track real endurance performance well from the mile up to the marathon. This calculator implements Cameron's published factor with distances in miles, scaling your known pace by the ratio of fatigue factors and the target distance. Enter your known time and distance plus the target distance, both in miles, to get a predicted time, pace, and the underlying fatigue factors.
Cameron formula
a(d) = 13.49681 - 0.000030363 * d + 835.7114 / d ^ 0.7905
Predicted time = (known time / known distance) * (a(known) / a(target)) * target distance
Distance d is in miles
The factor a(d) decreases gradually as distance grows, encoding the slowdown of distance running. Both distances must be entered in miles for the published factor to apply correctly.
Common distances in miles
- 5K is 3.10686 miles; 10K is 6.21371 miles.
- Half marathon is 13.10940 miles; marathon is 26.21880 miles.
- Cameron's model is intended for roughly the mile through the marathon.
- The U.S. Centers for Disease Control and Prevention recommends building distance gradually to limit injury risk.
- Course profile, weather, and pacing all move the real result away from any prediction.
Cameron prediction: frequently asked questions
What is Cameron's race prediction formula?
Cameron's formula predicts a finish time at a new distance from a known result. Unlike a single fixed exponent, it uses a distance-dependent fatigue factor a(d) = 13.49681 minus 0.000030363 times distance plus 835.7114 divided by distance to the power 0.7905, with distance in miles. The predicted time scales the known pace by the ratio of these factors and the new distance.
How does Cameron differ from the Riegel formula?
Riegel uses a single constant exponent (about 1.06) for all distances. Cameron's fatigue factor changes smoothly with distance, which many runners find gives more realistic predictions across a wider range, particularly from short races up to the marathon.
What distance units does this calculator use?
Cameron's published factor is defined with distance in miles, so this calculator takes both distances in miles. The factor formula is specific to that unit; entering kilometers would change the fatigue factor and produce an incorrect result.
How accurate is the Cameron prediction?
Like all such models it assumes you are well trained for the target distance and run an even effort. It works best between about one mile and the marathon. Fueling, course profile, weather, and pacing discipline all affect the real result, so treat the prediction as a realistic target rather than a certainty.
Can I predict a shorter race from a longer one?
Yes. The formula is symmetric in the sense that you can set the known distance longer than the target. Predicting a short race from a long one usually gives a conservative time because most runners have more raw speed than their long-distance results suggest.
Official sources
- USA Track & Field: running and coaching resources.
- U.S. Centers for Disease Control and Prevention: Physical Activity.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.