Race Time Predictor
Use a recent race result to estimate equivalent performances at other distances with the classic Riegel power-law formula. Large jumps and 50K predictions should be treated as rough extrapolations rather than guarantees.
About These Predictions
The core prediction uses the classic Riegel relationship: T2 = T1 × (D2 / D1)^1.06. That makes this page a simple equivalent-performance calculator rather than a full coaching model.
Optional Hilliness Estimate: If you enter elevation gain for the reference race, the page shows a rough flat-equivalent estimate based on the Minetti slope-cost model plus a symmetric climb/descent assumption. Total gain alone cannot capture the full course profile, so this adjustment should be treated as approximate.
Extrapolation Limits: Predictions become less trustworthy when the target distance is far from the reference race, and 50K is an extrapolation beyond marathon distance. Use those outputs as a planning reference, not a promise.
Primary Sources: Read the original Riegel article and the Minetti slope-cost paper used for the optional hilliness estimate: Riegel (1981) PDF | Minetti et al. on PubMed
How to Use These Predictions
Use a recent race result that reflects your current fitness, select metric or imperial units, and enter a custom target distance only if you need something beyond the standard outputs.
Custom Targets: A custom target distance is useful for races like 10 miles, 15K, 25K, or 30K. The same Riegel formula is applied, so the estimate is strongest when the target is reasonably close to your reference race.
Important Note: These predictions do not know your training history, weather, fueling, or race-day execution. For course-specific pacing with elevation profiles, use the Race Planning calculator instead.
Frequently Asked Questions
Found an error or have suggestions? Please email me at info@bflcoaching.com