The predicted times show what you might realistically run at other distances if you trained and paced appropriately for each. They are projections based on a mathematical relationship, not guarantees — actual results depend heavily on distance-specific training, pacing execution, and race-day conditions.

Per-mile and per-kilometer pace figures are provided so you can use them directly for pacing strategy or setting a GPS watch alert during training and racing.

Use this calculator when setting a goal time for an upcoming race at a distance you haven't run recently, when choosing which training plan intensity fits your current fitness, or when developing a pacing strategy from a known fitness benchmark.

It's most useful when your known result is a genuine, recent maximal effort at a comparable distance to the one you're predicting.

Riegel's formula assumes consistent training and pacing ability across distances, which doesn't hold for runners who specialize heavily in one distance without building the endurance base for longer ones. It also doesn't account for course terrain, weather, altitude, or race-day variables like nutrition and pacing execution.

Predictions become less reliable the further apart the known and target distances are — predicting a marathon from a mile time is far less reliable than predicting a 10K from a 5K time.