Heart Rate Zone Calculator: Karvonen Training Zones
Training by heart rate turns effort from guesswork into data. This free heart rate zone calculator computes your five training zones with the Karvonen method — which personalizes targets using your resting heart rate, not just age — so your easy days are truly easy and your hard days are truly hard.
How the Heart Rate Zone Calculator Works
Karvonen formula: Target HR = resting HR + (max HR − resting HR) × intensity %
The term in parentheses is your heart rate reserve (HRR) — the range your heart can actually expand into during exercise. Max HR is estimated as 220 − age unless you enter a tested value. Because Karvonen anchors to your resting HR, two athletes with the same max but different resting rates get genuinely different zones — which is why it tracks perceived effort far better than plain percentage-of-max math.
The Five Training Zones
| Zone | % of reserve | Feels like | Trains | |---|---|---|---| | Z1 Recovery | 50–60% | Very easy, conversational | Blood flow, recovery | | Z2 Fat burn | 60–70% | Easy, can hold conversation all day | Aerobic base, fat metabolism | | Z3 Aerobic | 70–80% | Moderate, short sentences | Cardiovascular fitness | | Z4 Threshold | 80–90% | Hard, few words | Lactate threshold, race pace | | Z5 VO2 max | 90–100% | Maximal, no talking | Top-end speed, VO2 |
Worked Example
A 35-year-old with a resting HR of 60:
- Max HR = 220 − 35 = 185 bpm
- Reserve = 185 − 60 = 125 bpm
- Z2 (60–70%): 60 + 125 × 0.60 = 135 to 60 + 125 × 0.70 = 148 bpm
- Z4 (80–90%): 160–173 bpm
Compare with naive %max zones (Z2 would be 111–130 bpm) — the Karvonen floor of 135 bpm reflects that this person's easy pace sits above a sedentary person's.
Measuring Your Resting Heart Rate
Resting HR is the personalization engine, so measure it well: take your pulse for 60 seconds right after waking (before sitting up or checking your phone), on 3 consecutive mornings, and average. Typical values run 60–100 bpm, with trained endurance athletes as low as 40–50. A resting rate that jumps 5–10 bpm above your normal for several days often signals insufficient recovery or incoming illness — free early-warning data.
Is 220 − Age Accurate?
It is a rough population average with a standard deviation of 10–12 bpm: at age 40, true max might be anywhere from ~168 to ~202. The Tanaka formula (208 − 0.7 × age) fits slightly better, especially past 45. If you train seriously, a field test beats both: after a thorough warm-up, do an 8-minute all-out effort (hill repeat or hard run) and watch the highest number your tracker records — that approximates your true max. Enter it in the calculator's override field.
Putting Zones to Work
The biggest mistake recreational athletes make is training in the middle — too hard to be easy, too easy to be hard. The evidence-based pattern (polarized training) is roughly 80% of weekly time in Z1–Z2 building the aerobic engine, and 20% in Z4–Z5 driving adaptation. Zone 2 is where fat metabolism, capillary density, and mitochondrial density improve — the base everything else sits on. Pair this structure with sensible fueling from our macro calculator and overall energy targets from the TDEE calculator.
Zone training presumes a healthy heart. Anyone with cardiac symptoms, diagnosed heart disease, or on rate-altering medication should get medical clearance before intensity training.