How to Use This Calculator
Enter your age and resting heart rate. The calculator uses the Karvonen formula (heart rate reserve) to generate five personalized training zones in bpm. A lower resting heart rate generally means better aerobic fitness, so two people the same age can end up with zones more than 10 bpm apart.
Formula & Background
Max HR (MHR) = 220 − age. Heart Rate Reserve (HRR) = MHR − resting HR. Target HR = (HRR × zone%) + resting HR.
Many watches draw zones from a straight percentage of max HR, which ignores individual fitness. Karvonen folds resting HR back in, so a trained person's Zone 2 sits higher than a sedentary person's — which matches how the effort actually feels.
The Five Heart Rate Zones
| Zone | % Max HR | Effort | Training Benefit |
|---|---|---|---|
| 1 — Warm-Up | 50-60% | Very easy | Recovery, warm-up |
| 2 — Fat Burn | 60-70% | Comfortable | Endurance base, fat oxidation |
| 3 — Aerobic | 70-80% | Moderate | Cardiovascular fitness |
| 4 — Threshold | 80-90% | Hard | Speed, lactate threshold |
| 5 — Maximum | 90-100% | All-out | Peak performance, VO2max |
Calculation Example
Age 30, resting HR 65 bpm: MHR = 190, HRR = 125.
Zone 2 = (125×0.60+65) to (125×0.70+65) = 140–153 bpm — aerobic base, the highest proportion of fat oxidation.
Zone 4 = 165–178 bpm — lactate threshold, race-pace work.
Which Zone Should You Train In
Endurance athletes tend to follow a rough 80/20 split: about 80% of training volume in Zone 2, the remaining 20% genuinely hard. Zone 2 means you can still hold a full sentence while moving. The common mistake is not training too easy — it is spending every session in Zone 3, which costs more than Zone 2 without delivering the Zone 4 stimulus.
Zone 5 intervals pay off but are expensive to recover from; cap them at one or two sessions a week with a day between.
How You Measure Matters
Wrist-based optical sensors are reasonable during steady running, but they lag or lock onto a wrong value during intervals and lifting, where heart rate swings fast. A chest strap is still substantially more reliable if you train by zones. Measure resting HR first thing in the morning before getting out of bed, averaged over several days — daytime readings run high.
Expert Tips
220 minus age is a population average with roughly ±10 to 12 bpm of individual variation; a lab VO2max test gives your actual max. If your morning resting HR trends 5+ bpm above normal for several days, that usually signals under-recovery or an oncoming illness — back off rather than push through.
If you have cardiovascular disease, take beta blockers (common in blood pressure medication), or have a pacemaker, these numbers do not apply — medication directly suppresses heart rate. Follow the exercise prescription from your physician.