What is the fat burning zone?

The fat burning zone is the heart rate range — typically 60-70% of maximum HR — where the body uses the highest percentage of fat (relative to carbohydrates) for fuel. It is commonly marketed on cardio machines, but the science is more nuanced than the marketing suggests.

Does the fat burning zone really burn more fat?

It burns the highest percentage of calories from fat, but not the most total fat. Higher intensities burn more total calories — and more total fat — even though carbs make up a larger share. For weight loss, total calorie deficit matters more than intensity zone.

When is the fat burning zone actually useful?

Long, sustainable Zone 2 sessions (60-70% max HR) build mitochondrial density, fat oxidation capacity, and aerobic base. They also accumulate volume without much fatigue, allowing more total weekly training. Endurance athletes use Zone 2 for the bulk of their training for these reasons — not for fat loss per se.

How do I know if I am in the fat burning zone?

A heart rate monitor is the most reliable way. As a field check, you should be able to hold a conversation in full sentences without gasping. If you can sing comfortably, you are below the zone. If you can only get out a few words, you are above it.

Plain percent vs Karvonen — which is more accurate?

Karvonen (HRR-based) accounts for resting HR, making it more individualized. Two people with the same max HR but different resting HRs will have different Karvonen zones — which better reflects their actual exercise stress. Plain percent of max is simpler but less personalized.

Fat Burning Zone Calculator

Find the heart rate range where the body draws the largest share of fuel from fat (60–70% max HR).

Calculator

About the Fat Burning Zone

The fat burning zone (also called Zone 2 in five-zone models) is most useful as a training tool rather than a weight loss strategy. It builds the aerobic base that supports higher-intensity work, improves recovery, and is sustainable enough to be done frequently.

Plain % vs Karvonen Method

Plain %: Target HR = Max HR × intensity (e.g., 0.65). Karvonen: Target HR = Resting HR + (HRR × intensity), where HRR = Max HR − Resting HR. Karvonen produces a higher target HR for fit people with low resting HR, better matching their actual perceived effort.

Formula

Plain %: Target HR = Max HR × intensity %

Karvonen: Target HR = Resting HR + (HRR × intensity %)

Fat Burning Zone Range

MethodLower BoundUpper Bound

Plain % of Max HR60% × Max HR70% × Max HR

Karvonen (HRR)Rest HR + 60% × HRRRest HR + 70% × HRR

Medical Disclaimer

Heart rate zones are individual and can vary by 10-15% from formula-based estimates. Lab testing or field tests give a more accurate personal zone.

Fat Burning Zone Calculator

About the Fat Burning Zone

Plain % vs Karvonen Method

Formula

Fat Burning Zone Range

Medical Disclaimer

Frequently Asked Questions

Related Calculators

Track Your Fat Burning Zone Over Time