Race Time Predictor

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.

Cross-Checked Range: For larger jumps we also run two independent models — Cameron (1999) and Daniels' VDOT — and show the fastest-to-slowest spread next to the Riegel time. When the models diverge (typically at marathon and beyond, where Riegel tends to be optimistic), that range is your honest margin of uncertainty; when they agree closely, no range is shown.

Optional Hilliness Estimate: If you enter elevation gain for the reference race, the page shows a rough flat-equivalent estimate. The climbing is priced with the same grade-cost model our coaching platform uses for adjusted pace and training load — a pace-realization curve, so it reflects the time a hill actually costs a runner rather than the extra oxygen it burns. Leave elevation loss blank and the descent is assumed to match the climb, which suits a loop or out-and-back; enter it for a point-to-point race so a net-downhill course is not priced as though it climbed back to the start. Either way the estimate works from totals, so it cannot know where the hills fall, and the adjustment stays 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 Minetti's slope-cost paper — the lab measurement of gradient energy cost that the grade model behind the hilliness estimate is anchored to: Riegel (1981) PDF | Minetti et al. on PubMed