How To Calculate Metabolic Age
If you still haven’t found your metabolic age, the easiest way to do it is by using my free metabolic age calculator. But if you’re curious about how to calculate metabolic age, I’ll show you the math.
The calculation for metabolic age involves a combination of both the Harris-Benedict formula and the Katch-Mcardle formula.
Men: BMR = 88.362 + ( 13.397 * Weight in kg ) + ( 4.799 * Height in cm ) – ( 5.677 * Age )
Women: BMR = 447.593 + ( 9.247 * Weight in kg ) + ( 3.098 * Height in cm ) – ( 4.33 * Age )
Because these equations don’t account for body composition, they are only accurate if you have “normal” body fat and muscle mass for your weight and age. For this reason, we’ll call this your “predicted BMR”.
Men & Women: BMR = 370 + ( 21.6 * Lean Mass in kg )
Most of the time, the Katch-Mcardle equation is more accurate since it takes your body composition into account. We’ll call this your “actual BMR”.
So if we plug your actual BMR back into the Harris-Benedict equation and solve for “Age” the result is your true metabolic age. With some simple algebra, the resulting equations for metabolic age look like this:
Metabolic Age Formula
Men: Metabolic Age = ( 88.362 + ( 13.397 * Weight in kg ) + ( 4.799 * Height in cm ) – Actual BMR ) / 5.677
Women: Metabolic Age = ( 447.593 + ( 9.247 * Weight in kg ) + ( 3.098 * Height in cm ) – Actual BMR ) / 4.33
Basically, this new equation compares the results of your actual BMR to your predicted BMR. The further you get from “normal” body composition, the bigger the difference between your actual age and metabolic age.
With my metabolic age calculator, I perform these calculations in the background including converting from pounds and inches to kilograms and centimeters. So all you have to do is enter your information to find your metabolic age.
When all is said and done, a high or low metabolic age doesn’t have much to do with your overall health or life expectancy. So it’s really just a tool to visualize the effect of body composition on your metabolism.
That being said, the metabolic age calculator shows how inaccurate the Harris-Benedict equation can be for finding your BMR and your ideal calorie intake. And this is the reason I use lean mass when creating your personalized meal plan.
One key takeaway is that you should always account for body composition when calculating your daily caloric needs. Especially when your lean mass or body fat is higher or lower than average.
If you found this calculator useful, make sure you check out some of my other great tools and content below!