Training Pace Calculator

VDOT is Jack Daniels' practical proxy for VO₂max — derived from actual race performance rather than lab testing. It represents your running economy + aerobic capacity combined. A VDOT of 50 means you can sustain ~50 ml/kg/min of oxygen uptake while running. All 5 training zones are then calculated as percentages of that value. As your fitness improves, your VDOT rises and all paces automatically shift.

Every time you race or run a genuine time trial. For most runners building a base, that's every 6–12 weeks. Don't update based on a great training run — only use all-out race efforts. Using outdated paces (from a slower period) means your Easy runs are too easy and your Threshold isn't hard enough.

Jack Daniels and most elite training frameworks use an 80/20 distribution: ~80% of weekly volume at Easy pace, ~20% at quality (T, I, or R). Most recreational runners do the opposite — too much moderate effort, not enough true Easy, not enough truly hard. The result is chronic fatigue without adequate adaptation stimulus.

That's intentional. Easy runs build mitochondrial density, capillary development, and fat oxidation — all of which happen optimally at 59–74% VO₂max. Going faster doesn't accelerate these adaptations; it just adds unnecessary stress. Elite Kenyan runners often run their Easy days at 6:00+/km despite racing marathons at 3:00/km. The gap is the point.