Race Time Predictor & VDOT Calculator

How this predictor works (The Riegel Formula)

This calculator relies on the standard **Riegel Formula**: T2 = T1 * (D2 / D1)^1.06, where T1 is your source time, D1 is your source distance, and D2 is the target distance. First published in 1977 by Peter Riegel, it accounts for the physiological decay in running velocity over longer distances. It assumes consistent aerobic training appropriate for the target distance.

VDOT vs. Riegel Predictions

While the Riegel formula is a solid general standard, coaches like Jack Daniels use **VDOT (oxygen consumption values)** to map running economy. VDOT values expect you to have optimized aerobic base capabilities. If you find your predicted marathon time is much faster than you can actually run, it indicates you are aerobic-capacity limited rather than speed limited, suggesting you need more Zone 2 training mileage.