A single recent race result is enough to estimate your VDOT — Jack Daniels' fitness score — and from that one number, derive the five paces that structure a serious training plan: Easy, Marathon, Threshold, Interval, and Repetition. The paces exist for different reasons, and running the wrong one on the wrong day is one of the most common training mistakes.

What VDOT actually measures

VDOT was introduced by coach Jack Daniels and exercise physiologist Jimmy Gilbert to solve a real problem: lab-measured VO2max alone doesn't predict race performance well, because running economy — how efficiently a runner converts oxygen into speed — varies a lot between athletes with similar VO2max. VDOT folds both into one number, estimated directly from a race result using two equations: one converts race velocity into an oxygen cost, the other estimates what fraction of VO2max a runner can sustain for that race's duration. Divide the first by the second and you get VDOT.

Because it's derived from an actual competitive effort, VDOT reflects your current fitness more reliably than a single lab test or a generic age-based formula.

Why five different paces

Each training pace targets a different physiological adaptation, all expressed as a percentage of vVDOT — the velocity at which oxygen demand equals your VDOT. Easy (62-75% of vVDOT) builds aerobic capacity and promotes recovery with minimal strain — it should feel genuinely conversational. Marathon pace (~77.5%) is the effort you could hold for 26.2 miles today. Threshold (~82.5%), often called tempo pace, is "comfortably hard" — sustainable for about an hour — and raises the pace at which lactate starts piling up faster than the body clears it. Interval (~92%) sits close to the velocity that maximizes oxygen uptake, run in 3-5 minute efforts to stress the aerobic ceiling. Repetition (~98%) is the fastest zone — short, fully-recovered repeats aimed at running economy and speed rather than aerobic fitness.

Running Easy days at Threshold effort (or faster) is the single most common way recreational runners sabotage their own training: it adds fatigue without the specific stimulus a hard day is supposed to provide, and it steals from the quality of the actual hard sessions.

Equivalent race times, and how this differs from a race predictor

Because VDOT is a fitness measure rather than a raw pace, it can predict performance at any distance: find the time that would produce the same VDOT at a different race length. This calculator solves that directly from the same two Daniels-Gilbert equations used to estimate VDOT in the first place — a genuinely different approach from the site's Race Predictor, which instead fits a Riegel or Cameron exponent to your raw race time. The two methods usually land close together, but VDOT-based equivalent times stay consistent with the training paces shown here, since both come from the same underlying model.

One important caveat: equivalent times and training paces both assume comparable training and racing experience at every distance. A 5K specialist's equivalent marathon time is optimistic if they've never trained for the distance-specific endurance a marathon actually demands.