This Is the Fat-Burning Heart Rate, With a Physiologist’s Reliable Formula

Updated: Mar. 01, 2024

How do you know when your workout is actually torching the excess energy your body's stored up as fat? Here's a simple calculation to get your body in the fat-burning zone, says one sports scientist.

Physical activity is beneficial for overall health, cardiovascular wellness, longevity and daily stress management. The Centers for Disease Control and Prevention (CDC) defines physical activity as anything that gets your body moving…and as Washington D.C.-based trainer Errick McAdams, CPT says: “All movement is good movement and anything beats the couch!”

The CDC recommends that adults get 150 minutes of moderate-intensity physical activity and two days of muscle-strengthening every week, based on the U.S. Department of Health and Human Services’ current Physical Activity Guidelines for Americans. But what is moderate intensity—and what if you’re looking to burn fat? Below, we tell you everything you need to know about your fat-burning heart rate.

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How to calculate the fat-burning heart rate

Alex Rothstein, MS, CSCS, EP-C, FMS, USAW, coordinator and instructor for the Exercise Science Program at New York Institute of Technology, recommends the Karvonen Formula to calculate your fat-burning heart rate. (We provide an example calculation for you to follow along with below.) “An individual subtracts their age from 220 to get their ‘age-predicted heart rate max,’ and then subtracts their resting heart rate from this number to get their heart rate reserve,” Rothstein says. “If you want to exercise at 75% of your heart rate reserve, you would multiply the heart rate reserve by 0.75 and then add back the resting heart rate. This new number would be the target heart rate to work at 75% of one’s heart rate reserve.” 

Start with the understanding that the Cleveland Clinic, which is consistently named one of the leading health systems in the country for cardiological care, suggests that a healthy resting heart rate, in general, lies between 60 and 100 beats per minute. (The American Heart Association backs this up and applies it to both genders.)

So, for a 43-year-old with a resting heart rate of 70:

  • 220 – 43 = 177
  • 177 – 70 = 107
  • 107 x 0.75 = 80.25
  • 80.25 + 70 = 150.25

So, 150 is the fat-burning heart rate for this individual.

What is the difference between the fat-burning zone and the cardio zone?

People are often surprised to learn that the fat-burning heart rate is less intense than the cardio zone—says Rothstein: “The cardio zone represents an intensity level that is higher and uses a greater percentage of carbohydrates. This cardio zone is also representative of a high-enough intensity to promote positive cardiovascular adaptation and improve an individual’s aerobic fitness.”

Physical activity is good for you and improves your health regardless of the intensity level. “Your whole workout doesn’t have to be in the fat-burning or cardio zone to be effective,” McAdams says, adding that if you don’t have a heart-rate monitor, you can typically tell that you’ve hit your fat-burning stride “if you’re working out and can’t talk in full sentences.” 

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How do I measure my heart rate?

Smartwatches and fitness trackers make monitoring heart rate convenient, though they’re slightly less accurate than the heart rate straps. “Heart rate straps have become relatively outdated due to the convenience and improved accuracy of wrist-worn monitors,” Rothstein says. “It still appears that the more accurate option is the heart rate strap, but the improved accuracy is minimal.”

Consider your age

Your heart rate adjusts as you age, and your heart becomes less powerful, so you don’t have to work out as hard at 50 as you do at 20 to get your heart rate into the same zone.

“With increased age, our age-determined heart rate maximum is lower,” Rothstein says, “so higher heart rates become representative of higher percentages of our heart rate reserve.”

Consider your size

We’re always burning fat and carbohydrates, though not always at the same rate. Rothstein points out that body size can impact fat and carbohydrate usage, as larger individuals require more oxygen for the same level of intensity. 

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Consider what fuel is available

“Another important variable is substrate availability,” Rothstein says, “which means that if carbs are readily available for use, they’re more likely to be used, while if carbs are not available (due to someone having fasted before exercise or having performed prolonged exercise), fat will be used.” Keep this in mind if you’re deciding whether or not to eat before a workout

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What are the best exercises for burning fat?

It makes sense that we’d want to stay in the fat-burning heart rate zone to burn fat, but that’s not true. “Contrary to popular belief, exercising in the fat-burning zone is not the best way to burn high amounts of fat,” Rothstein says. “A better way to burn fat is to exercise at higher intensities because the total caloric expenditure will be the greatest.” 

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“Some examples include running, indoor cycling, rowing, and swimming,” explains Matt Claes, founder & head coach at Weight Loss Made Practical. “But that being said, keep personal preference and injury risk in mind because you’ll want to do your fat-burning workouts consistently.”

Rothstein also reminds readers that resistance training provides benefits that cardiovascular training alone or dieting alone will not. “Resistance training improves body composition, increases strength and improves quality of life,” Rothstein says. “Plus, it increases muscle mass and thereby increases metabolism.”

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For weight loss, Rothstein recommends:

“Remember that HIIT training doesn’t have to be a sprint on a treadmill with an incline,” Rothstein says. “Any form of interval training where the intensity increases followed by a rest period of lower intensity is considered HIIT and can be extremely beneficial for both fat burning through caloric expenditure and cardiovascular health.”

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