❤️ Heart Rate Zones Calculator

Heart Rate Zones Calculator - Training Smarter With the Right Intensity

Most recreational exercisers train at the same moderate intensity for every session - not too easy, not too hard. This "moderate always" approach is actually the least effective training distribution. Research and professional coaching consistently show that mixing structured low-intensity training (Zone 2) with occasional high-intensity work (Zone 4–5) produces better aerobic development, faster recovery, and better long-term fitness than constant moderate effort.

The 5 Training Zones - What Each One Does

Karvonen vs Max HR Method - Which Is More Accurate?

The simple Max HR percentage method uses: Target HR = Max HR × Zone%. It's quick but doesn't account for your fitness level. Two people with the same age and identical max HR (185 bpm) will have very different cardiovascular fitness if one has a resting HR of 45 and the other 80. Their "Zone 2" should not be the same.

The Karvonen Heart Rate Reserve method uses: Target HR = ((Max HR − Resting HR) × Zone%) + Resting HR. By incorporating resting HR (which reflects aerobic fitness), it creates zones that are genuinely personalised to your current fitness level. A fit person's Zone 2 will be higher in absolute bpm than a deconditioned person's Zone 2, even with the same max HR.

Use Karvonen if you know your resting HR. It requires one extra input but produces more accurate and meaningful training zones.

Zone 2 Training - The Evidence Behind the Hype

Zone 2 has received enormous attention in endurance sports and longevity research in recent years, largely through work by exercise physiologist Iñigo San Millán (who coaches Tour de France cyclists) and researcher Peter Attia. The key evidence-backed benefits:

• Mitochondrial biogenesis: Zone 2 is the primary stimulus for creating new mitochondria and improving existing mitochondrial function. More and better-functioning mitochondria means better aerobic efficiency at all intensities.
• Fat oxidation efficiency: Training consistently in Zone 2 improves the body's ability to use fat as a fuel at higher intensities - this "metabolic flexibility" is central to both endurance performance and metabolic health.
• Recovery tolerance: Low-intensity training produces significant aerobic adaptation with minimal fatigue - allowing more total training volume and faster recovery between hard sessions.
• Cardiovascular health benefits: Zone 2 training is associated with measurable improvements in resting heart rate, blood pressure, and cardiac function even in sedentary individuals who add 3–4 hours per week.

The practical implication: if you currently do most of your cardio at a pace that's "challenging but not terrible," slowing down significantly for 70–80% of your sessions while adding occasional genuine hard intervals (Zone 4–5) is likely to improve your fitness more than always staying in Zone 3.

Training Zone Distribution - The Polarised Model

Elite endurance athletes (marathon runners, triathletes, cyclists) typically distribute their training approximately as follows, a pattern called "polarised training":

• Zone 1–2: 70–80% of total weekly training time - easy, conversational pace, building aerobic base
• Zone 3: 5–10% - some research suggests this "moderate" zone may actually be the least productive and should be minimised
• Zone 4–5: 15–20% - quality sessions, intervals, threshold work

For beginners and recreational exercisers, a simpler approach: do the majority of sessions at a pace where you can hold a conversation (Zone 2), and once per week do an interval session or tempo run that genuinely challenges you (Zone 4). This avoids the "moderate always" trap and builds both aerobic base and speed simultaneously.