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Calculate race pace per mile or kilometer, finish time, and split times for any distance. Plan pacing for 5K, 10K, half marathon, and marathon.
Estimate VO2 max from race times, Cooper 12-minute test, or resting heart rate. Measure aerobic fitness for running and cycling training.
Calculate even, negative, or progressive split times for race distances. Plan mile or kilometer checkpoints for marathon and half marathon pacing.
220 − age is a population average with ±10–12 bpm individual error. Field tests (3-min all-out effort) or lab tests give better personal max HR values.
Estimated max HR = 220 − AgeTarget HR = ((Max HR − Resting HR) × Intensity%) + Resting HR. Accounts for individual fitness — fit athletes have larger HR reserve.
Target HR = (HRR × Zone%) + Resting HRZone 1 (recovery): 50–60% HRR. Zone 2 (aerobic): 60–70%. Zone 3 (tempo): 70–80%. Zone 4 (threshold): 80–90%. Zone 5 (VO2 max): 90–100%.
Zone boundaries = Karvonen at zone % limitsUpdated: July 2026
Max HR 185, resting HR 52. HRR = 133. Zone 2 (easy): 132–145 bpm. Zone 4 (threshold): 158–172 bpm. Zone 5 (intervals): 172–185 bpm.
Threshold HR from 30-min time trial average (e.g., 168 bpm). Zone 2 below 85% threshold (~143 bpm). Threshold work at 95–100% (~160–168 bpm).
Age 45, max HR 175. Simple percentage zones: easy below 122 bpm (70%), moderate 122–149 (70–85%), hard above 149 (85%+). Upgrade to Karvonen as fitness improves.
Zone 3 feels comfortably hard but accumulates fatigue without optimal easy-day recovery or hard-day stimulus. Slow down until HR drops into Zone 2 — often 60–90 sec/mile slower than expected.
Max HR declines slowly with age but medications (beta blockers) and fitness changes alter zones. Retest max HR or use recent race data every 1–2 years.
Training by heart rate zones ensures easy days stay easy and hard days hit the right intensity. Zones can be set from maximum heart rate percentages or the more accurate Karvonen (heart rate reserve) method using resting HR. This calculator generates zone boundaries for endurance training.