Heart Rate Zones Calculator

Zone 1 (50–60% max HR): very light — warm-up, cool-down, and active recovery. Zone 2 (60–70%): light aerobic — fat-burning, base endurance, mitochondrial development. Zone 3 (70–80%): moderate — sustained aerobic effort, "comfortably hard". Zone 4 (80–90%): hard — lactate threshold, high-intensity intervals. Zone 5 (90–100%): maximum — peak power, sprint efforts, can only be sustained for seconds to a few minutes.

Zone 2 training is aerobic exercise at 60–70% of your maximum heart rate — a pace where you can hold a conversation but feel like you're working. It is the most researched training zone for long-term health and endurance performance. Benefits of regular Zone 2 training include: increased mitochondrial density (cellular energy production), improved fat oxidation (using fat as primary fuel), enhanced cardiovascular efficiency, and lower resting heart rate. Most endurance coaches (including Peter Attia, Phil Maffetone, Stephen Seiler) recommend 70–80% of total weekly training time in Zone 2.

MAF (Maximum Aerobic Function) is a method developed by endurance coach Dr. Phil Maffetone to define your optimal aerobic training heart rate. The MAF formula is simply 180 minus your age. For a 35-year-old: MAF HR = 180 − 35 = 145 bpm. This is an upper ceiling for fully aerobic training — staying below it ensures you develop fat-burning capacity and avoid over-reaching. Adjustments: subtract 5 if you are recovering from illness or overtraining; add 5 if you are a highly trained athlete with several years of consistent training.

The most common formula is 220 − age. For a 35-year-old: max HR = 220 − 35 = 185 bpm. A more precise alternative is the Tanaka formula: 208 − (0.7 × age), which gives slightly higher values for older adults. For example, at age 50: standard formula gives 170 bpm, Tanaka gives 173 bpm. Neither formula is precise for individuals — actual max HR can vary by ±10–20 bpm from the estimate. The most accurate measurement is a laboratory maximal exercise test or a field test (e.g., all-out 1-mile run).

The Karvonen method calculates target training heart rate using your heart rate reserve (HRR = max HR − resting HR). Target HR = resting HR + (HRR × zone intensity%). Example for a 35-year-old with a resting HR of 55 bpm: max HR = 185, HRR = 130. Zone 2 (60–70%): 55 + (130 × 0.60) to 55 + (130 × 0.70) = 133–146 bpm. The Karvonen method is more accurate than the simple percentage-of-max because it accounts for your individual cardiovascular fitness — a trained athlete with a low resting HR gets higher zone targets than an untrained person of the same age.

Zone 2 (60–70% max HR) is the primary fat-burning zone — at this intensity, fat provides ~60–70% of total energy. However, Zone 3–4 burns more total calories per hour even though a lower percentage comes from fat. For sustained fat loss and metabolic health, Zone 2 training is superior long-term: it increases fat-oxidation capacity, improves insulin sensitivity, and can be sustained for long durations without excessive recovery needs. Most people aiming for body composition improvement benefit from 3–5 Zone 2 sessions per week of 45–90 minutes.

Zone 2 (60–70% max HR) feels easy to moderate — you can speak in full sentences, breathing is elevated but controlled, and you could sustain the effort for 1–3+ hours. Zone 3 (70–80% max HR) is "comfortably hard" — talking becomes difficult, you can speak in short phrases, and the effort is sustainable for 30–90 minutes. Zone 3 crosses into carbohydrate-dominant metabolism and begins accumulating lactate. Many amateur athletes train too often in Zone 3, which research calls the "moderate intensity trap" — generating fatigue without the aerobic adaptations of Zone 2 or the performance benefits of Zone 4–5.

Measure your resting HR first thing in the morning before getting out of bed — ideally after lying still for 5 minutes after waking. Count your pulse at your wrist or neck for 60 seconds (or 30 seconds × 2). Average adult resting HR: 60–80 bpm. Trained endurance athletes: 40–60 bpm. Elite cyclists and runners: sometimes 28–40 bpm. A resting HR above 100 bpm (tachycardia) or below 40 bpm in a non-athlete warrants a medical check. Smartwatches and heart rate monitors measure resting HR automatically — useful for tracking trends over weeks and months.

The "polarised training" model — supported by research from Dr. Stephen Seiler — recommends: 70–80% of sessions in Zone 1–2 (easy aerobic), 5–10% in Zone 3 (moderate), and 15–20% in Zone 4–5 (high intensity). For a typical recreational athlete training 5 days/week: 3–4 sessions in Zone 2 (long easy runs, cycling, swimming), 1 session with Zone 4–5 intervals, 0–1 moderate Zone 3 session. Many amateur athletes invert this pyramid — training too hard on easy days and too easy on hard days — reducing the benefit of both.

This calculator provides zone estimates based on age-predicted maximum heart rate (220−age or Karvonen formula). Individual accuracy varies: the 220−age formula has a standard deviation of ±10–12 bpm, meaning a 35-year-old's actual max HR could be anywhere from 163–207 bpm. The Karvonen method improves accuracy by using your actual resting HR. For the most precise zones, consider a lactate threshold test or VO2 max test with a sports physiologist, or use a heart rate monitor with a dedicated maximal field test protocol.