Running pace calculator.
VDOT paces and race predictions.

How to use your paces

What VDOT measures

VDOT is a fitness score from the exercise physiologist Jack Daniels. It estimates how much oxygen your body uses when you run, the same thing a lab VO2max test measures, but read straight off a race result instead of a treadmill and mask. The logic is simple: if you can run a 5K in a given time, the physiology that produced it also predicts the right speed for every other kind of training. One number, drawn from one honest effort, unlocks your whole week. The fresher and harder that race, the truer the paces, so feed it a hard run from the last month, not a personal best from two years ago.

What each pace zone is for

Your easy pace is the bulk of your week. It builds your aerobic engine with little fatigue cost, and it should feel almost annoyingly slow. It is shown as a range, so run anywhere inside that band. Your marathon pace is a touch faster, the steady effort you could hold for the full distance, used mainly in marathon blocks. Your threshold pace is comfortably hard, the speed you could race for about an hour. Tempo work here raises the ceiling so race pace feels easier. Your interval pace is hard, around your VO2max, run in three to five minute repeats. This is the zone that actually lifts your fitness score. Your rep pace is faster still, short fast reps with full recovery, training leg speed and economy so every other pace costs less.

Notice how wide the spread is between easy and interval. That gap is the entire system. Run your slow days genuinely slow and your hard days can be genuinely fast. Running easy days too hard is the single most common reason runners plateau: every day becomes a medium grind, too taxing to recover from and too gentle to drive real adaptation.

Why race prediction works

The predicted finish times come from Pete Riegel's endurance formula, a clean relationship fitted from thousands of race results: your predicted time equals your known time multiplied by the ratio of distances raised to the power 1.06. That exponent captures how you slow down as distance grows. The prediction is sharp within roughly double your race distance, so a 10K from a 5K is reliable, while a marathon from a 5K runs optimistic because it assumes your endurance scales perfectly when it rarely does. Use the longer predictions as a target ceiling and a recent longer race to anchor them. Either way, you now have numbers instead of guesswork: what to run in training, and what your current fitness is worth on race day.