What is the fat-burning zone?

The fat-burning zone is typically Zone 2 of the five-zone heart-rate model, sitting at 60–70% of your maximum heart rate. At this intensity your aerobic system can supply enough oxygen to use fat (via beta-oxidation) as the dominant fuel. Although the percentage of calories from fat is actually higher at very low intensities, the absolute amount of fat burned per minute peaks in this 60–70% range — which is why it earns the "fat-burn zone" label.

How is maximum heart rate (HRmax) estimated?

The calculator offers three validated formulas. Standard (220 minus age) is the most widely known but has high individual variability (plus or minus 10–12 bpm). Tanaka (208 minus 0.7 times age) is derived from a 2001 meta-analysis of 351 studies and is more accurate for adults. Gelish (207 minus 0.7 times age) is similar. For the most accurate result, measure your own HRmax by entering it as a custom value in the optional override field.

What is the Karvonen formula?

The Karvonen method (also called the Heart Rate Reserve method) accounts for your resting heart rate when setting zones. Target HR = (HRmax minus HRrest) times intensity% plus HRrest. Because it uses your heart rate reserve (HRmax minus HRrest), it produces personalised zones that are tighter and more meaningful than simple percentage-of-HRmax zones. A well-trained athlete with a resting HR of 45 bpm gets very different Zone 2 targets to a sedentary person with a resting HR of 80 bpm, even if both have the same HRmax.

How accurate is the fat oxidation estimate?

The g/min figure is a population-level approximation based on Achten and Jeukendrup (2003) and scaled by body weight. Individual fat oxidation varies considerably with aerobic fitness, diet (especially carbohydrate intake), time since last meal, and genetics. Highly trained endurance athletes can oxidise 0.8–1.0 g/min at peak; untrained individuals are closer to 0.3–0.5 g/min. Use the figure as a directional guide, not a precise measurement.

Should I always train in the fat-burning zone to lose weight?

Not necessarily. While Zone 2 burns the highest proportion of fat, higher-intensity training burns more total calories per minute and can elevate metabolism for hours afterward (EPOC effect). A well-rounded programme combines Zone 2 base work for fat oxidation and aerobic efficiency with some Zone 4–5 intervals for calorie burn and fitness. Zone 2 is particularly valuable for those building an aerobic base or recovering between hard sessions.

How do I measure my resting heart rate accurately?

Lie still for 5 minutes after waking — before checking your phone or getting out of bed. Count your pulse for 60 seconds (or 30 seconds and double it), or use a heart-rate monitor. Average three consecutive mornings for the most reliable number. Resting HR for adults typically ranges from 60–100 bpm; endurance athletes often sit at 40–60 bpm.

Fat-Burning Zone Calculator

Your body always burns a mix of fat and carbohydrate for fuel. The ratio of that mix shifts dramatically with exercise intensity, and the fat-burning zone is the heart-rate range where the absolute amount of fat oxidised per minute reaches its peak. This calculator gives you that range in beats per minute, personalised to your age, resting heart rate and body weight, along with your full five-zone breakdown and an estimated fat-oxidation rate for each zone.

How it works

Every calculation starts with your maximum heart rate (HRmax). The tool offers three validated formulas: the classic Standard (220 minus age), the Tanaka formula (208 minus 0.7 times age) derived from a 2001 meta-analysis across 351 studies, and the near-identical Gelish formula (207 minus 0.7 times age). If you have tested your true HRmax in a supervised test, enter it in the custom-override field for the best accuracy.

From HRmax the calculator derives five training zones using either the basic method (a straight percentage of HRmax) or the more personalised Karvonen (Heart Rate Reserve) method:

Target HR = (HRmax − HRrest) × intensity% + HRrest

The Karvonen method matters most for people with very low or very high resting heart rates. A resting HR of 45 bpm (trained athlete) versus 80 bpm (sedentary beginner) shifts the absolute bpm targets substantially even when HRmax is identical.

The fat-oxidation rate shown in the table (g/min) is estimated using a parabolic model calibrated on Achten and Jeukendrup’s landmark 2003 study, then scaled by body weight. Fat oxidation peaks at approximately 65% of HRmax and falls off at both lower and higher intensities. Multiplying by 9 kcal/g converts grams to kilocalories.

Worked example

A 35-year-old, 70 kg, with a resting HR of 60 bpm using the Tanaka formula and Karvonen method:

HRmax = 208 minus (0.7 times 35) = 208 minus 24.5 = 183.5 → 184 bpm
Heart Rate Reserve (HRR) = 184 minus 60 = 124 bpm
Zone 2 lower (60%): 124 times 0.60 plus 60 = 74.4 plus 60 = 134 bpm
Zone 2 upper (70%): 124 times 0.70 plus 60 = 86.8 plus 60 = 147 bpm
Fat-burn zone: 134–147 bpm
Estimated fat oxidation (Zone 2 midpoint ~65%): ~0.39 g/min → ~3.5 kcal/min from fat

Using the basic method instead (no resting HR):

Zone 2 lower = 184 times 0.60 = 110 bpm
Zone 2 upper = 184 times 0.70 = 129 bpm

The Karvonen range is noticeably higher because this person’s 60 bpm resting HR shifts the reserve-based targets upward compared to the raw percentage calculation.

Zone	% HRmax	Purpose	Primary fuel
1 — Very Light	50–60%	Recovery, warm-up	Fat (high %)
2 — Light	60–70%	Fat-burn peak	Fat (highest g/min)
3 — Aerobic	70–80%	Endurance base	Fat + carbs
4 — Threshold	80–90%	Lactate threshold, tempo	Mostly carbs
5 — Maximum	90–100%	Sprints, HIIT peaks	Almost all carbs

Formula note

The Achten and Jeukendrup fat-oxidation model shows that fat use rises as intensity increases from rest up to roughly 65% HRmax (called the FATmax point), then falls steeply as carbohydrate metabolism takes over. Above approximately 85–90% HRmax, fat oxidation approaches zero because the aerobic pathway cannot keep pace with energy demand. This is why long, steady Zone 2 sessions — not all-out sprints — are the foundation of fat-loss and metabolic health programmes in elite endurance coaching.

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