How Race Predictions Work

The Riegel formula — T2 = T1 × (D2/D1)^1.06 — models how your pace slows as distance increases. Derived from elite performance data, it estimates what your current fitness would produce at another distance. It is a planning tool: pick realistic goal times, then train specifically for the target distance.

Getting a Reliable Reference

Use a recent race at hard, consistent effort on a fair course. Training runs, extreme weather, or significant elevation changes distort predictions. The more race-like your reference effort, the more trustworthy the output.

Limitations

Predictions assume endurance-specific training for the target distance. A 5K-derived marathon prediction is optimistic unless you have marathon-long runs in your build. Treat results as target bands (±2–3%), not guarantees.