Which heart rate zone burns the most fat?

Zone 2 (60–70% of heart rate reserve) maximises the proportion of calories from fat. Higher zones burn more total calories but a smaller proportion from fat.

How accurate are wearable devices at measuring heart rate during exercise?

Optical heart rate sensors in wrist-worn devices work by shining light through the skin to detect blood flow. They are reasonably accurate during steady-state activities like walking or cycling, but can struggle during high-intensity interval training, weightlifting, or activities involving significant wrist movement, where readings may lag or be unreliable by 10–20 bpm. A chest strap monitor paired with a running watch provides considerably more accurate and real-time data for precision heart rate training.

Heart Rate Zone Calculator

When to use this calculator

Before setting a new health goal or checking whether a plan is realistic.
When you want a quick baseline before discussing the result with a professional.
When you are starting a fitness or diet programme and want a starting measurement.
When you want to recheck the numbers after several weeks of change.

A worked example

These are the example figures the calculator opens with.

A worked example
Input	Value
Age	35
Resting Heart Rate (bpm)	65

For those figures the calculator returns:

Max HR: 185.00 bpm
Fat burn: 125.00-137.00
Aerobic: 137.00-149.00
Threshold: 149.00-161.00
VO2 max: 161.00-173.00

Method & assumptions

Heart rate zone calculators estimate your training zones based on your maximum heart rate (MHR), which is most commonly approximated using the formula 220 minus your age. More accurate results can be achieved using the Karvonen formula, which incorporates your resting heart rate to calculate Heart Rate Reserve and produces personalised zone thresholds. Each zone corresponds to a different physiological effect and training stimulus. It is worth understanding that MHR formulas are population averages — individual maximum heart rates can vary by 10 or more beats per minute from what the formula predicts. Wearable devices using optical heart rate sensors also introduce measurement error. For accurate zone calibration, a supervised exercise test with a sports physiologist is the gold standard approach.

Common mistakes

Using an assumption that is not supported by a current local quote, bill, statement or official source.
Treating a generic estimate as a lender, provider, payroll or tax authority decision.
Mixing monthly and annual inputs without converting them consistently.
Testing only one scenario instead of checking how a cautious assumption changes the result.

What to do next

Run a second scenario with a cautious assumption so you can see the downside clearly.
Compare the result with the related calculators below before making a decision.
Check current local rules, eligibility and provider terms before applying or committing money.
Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.

Keep exploring

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Questions people ask

The 220-minus-age formula gives a rough estimate. A more accurate method is a maximal effort test (e.g. running uphill to exhaustion) under professional supervision.