Predict your marathon time and get science-backed training paces using the Jack Daniels VDOT system, Riegel formula, and more.
📚 Jack Daniels VDOT📐 Riegel (1977) Formula🔬 Karvonen HR Zones⚡ 80/20 Training (Fitzgerald)📊 Pfitzinger Methodology
🏃 Enter Your Best Recent Race
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Used to estimate max HR if not entered
Heart Rate Optional — improves HR zones
Leave blank to use 220 − age formula
Morning resting HR (leave blank for default 60)
Pacing Strategy
Display Units
Predicted Marathon Time
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VDOT (VO₂max est.)
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Marathon Pace /km
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Marathon Pace /mile
📊 Jack Daniels VDOT Training Paces
⏱️ Marathon Pace Band
💡 Pacing research: Studies show runners who start at predicted marathon pace or slightly slower (negative split) outperform those who go out too fast. A 2–4% negative split is associated with optimal performance (Renfree & Gibson, 2013).
❤️ Heart Rate Training Zones
80/20 Rule (Fitzgerald, 2014): Evidence from elite athletes shows ~80% of training should be in Zone 1–2 (low intensity), with only ~20% in Zone 3–5. This polarised distribution optimises aerobic adaptation while minimising injury and overtraining risk.
⚡ Glycogen Depletion / Bonk Risk
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📚 Evidence Base & References
Riegel (1977) — Riegel, P.S. Athletic Records and Human Endurance. American Scientist, 69, 285–290.
Jack Daniels (2005) — Daniels, J. Daniels' Running Formula (2nd ed.). Human Kinetics.
Karvonen et al. (1957) — Effects of training on heart rate. Annales Medicinae Experimentalis, 35(3), 307–315.
Fitzgerald (2014) — Fitzgerald, M. 80/20 Running. NAL Trade.
Pfitzinger & Douglas (2009) — Advanced Marathoning (2nd ed.). Human Kinetics.