Abel's Calculators

VDOT (Jack Daniels) is your aerobic capacity expressed as an equivalent VO2max value derived from a race performance. It's calculated from both your pace (how fast you ran relative to the distance) and the fractional utilization of VO2max at that effort level. Two runners with the same VDOT are aerobically equivalent and should predict nearly identical times at any distance — differences in results come from specificity of training, pacing, and course conditions.

Mileage adjustment accounts for the fact that VDOT from a 5K doesn't perfectly translate to marathon performance unless you're training at marathon-specific mileage. Under-trained runners see a larger gap between VDOT-predicted times and actual performance at longer distances. The penalty scales with how much your weekly mileage falls below the ideal for your target race, and how much longer the target is vs your PR distance. It's capped at 10% and only applies when the target is longer than the PR and both are beyond 10K.

Elevation adjustment normalizes race times to a flat-equivalent effort. Each 1% average uphill grade adds roughly +1.2% to your pace, while each 1% average downhill grade saves only -0.6% — uphills hurt more than downhills help. Your PR time is converted to a flat-equivalent time using your PR course's elevation, then VDOT is computed from that. The predicted time is then adjusted upward by your target course's elevation factor.

Formula source: Jack Daniels, Daniels' Running Formula. The VDOT model was originally published in Medicine & Science in Sports (Daniels & Gilbert, 1979). Predictions are estimates — individual performance varies based on pacing, weather, course, and race-day conditions.