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Fat Burning Zone Calculator

Calculate target heart rate zones for maximum fat oxidation using the Karvonen formula. Determine aerobic vs anaerobic thresholds.

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About

Effective fat loss requires more than just moving; it requires precision. The common belief that "harder is better" often leads to overtraining and glucose depletion rather than fat oxidation. This tool utilizes the Karvonen Method, a robust algorithm that factors in your Resting Heart Rate (RHR) to calculate intensity zones tailored to your specific cardiovascular efficiency. Unlike the basic 220 − Age equation, which treats all individuals of the same age identically, the Karvonen formula adjusts the target floor and ceiling based on your fitness level.

By staying within the calculated Fat Burning Zone (typically Zone 2), you maximize the body's reliance on lipids for fuel while preserving muscle glycogen. This calculator determines five distinct intensity tiers, from recovery to maximum output, ensuring every minute of cardio serves a specific physiological purpose.

heart rate cardio fat loss karvonen training zones

Formulas

The calculation proceeds in two stages. First, we estimate the theoretical maximum heart rate (MHR), and then we determine the Heart Rate Reserve (HRR) to apply the target intensity (I).

1. Maximum Heart Rate:

MHR ≈ 220 − Age

2. Heart Rate Reserve:

HRR = MHR − RHR

3. Karvonen Target Zone:

Target = (HRR × I) + RHR

Where I represents the desired intensity percentage (e.g., 0.65 for 65%).

Reference Data

ZoneIntensity RangePhysiological BenefitFuel Source
Zone 150-60%Warm Up & RecoveryFat (Primary), Glycogen (Low)
Zone 260-70%Maximum Fat OxidationFat (Maximized)
Zone 370-80%Aerobic EnduranceGlycogen & Fat Mix
Zone 480-90%Anaerobic CapacityGlycogen (Primary)
Zone 590-100%VO2 Max / SpeedGlycogen, Creatine Phosphate
ReferenceMHR EstimateMaximum Heart RateN/A
Standard220 − AgePopulation AverageN/A
MetricHRRHeart Rate ReserveN/A

Frequently Asked Questions

The standard formula does not account for individual fitness levels. Two 40-year-olds can have vastly different resting heart rates (e.g., 50 bpm vs. 80 bpm). The Karvonen formula incorporates the Resting Heart Rate (RHR), narrowing the target zones to match your actual cardiovascular reserve.
For the highest accuracy, measure your pulse immediately upon waking up, before getting out of bed or consuming caffeine. Take the average over three consecutive mornings to establish a reliable baseline.
Training in Zones 3, 4, or 5 shifts the body's fuel preference from fatty acids to muscle glycogen (carbohydrates). While this improves cardiovascular performance and speed, it is less efficient for direct fat oxidation and requires longer recovery times.
As cardiovascular fitness improves, your RHR will typically decrease. Re-calculate your zones every 4 to 8 weeks to ensure your training intensity remains effective relative to your new fitness level.