Metabolic Age Calculator
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Metabolic age compares how many calories your body burns at rest with the average for people of your sex and size at different ages. More muscle means a higher resting burn and a younger metabolic age. Body fat makes the estimate much better; leave it blank to estimate it from BMI.
| Metabolic age | 31 years |
| Actual age | 40 |
| Your BMR (from lean mass) | 1399 kcal/day |
| Average BMR at your age | 1351 kcal/day |
| Body fat | 30% |
| Lean body mass | 47.63 kg |
Show steps
- Body fat: 30%.
- Lean mass = 68.04 kg × (1 − 0.3) = 47.63 kg.
- Your BMR from lean mass (Katch–McArdle): 370 + 21.6 × 47.63 = 1,399 kcal/day.
- Average BMR for your sex, height and weight at your age (Mifflin–St Jeor): 1,351 kcal/day.
- Metabolic age = the age at which the Mifflin average equals your BMR: (1,551.3 − 1,399) ÷ 5 = 30.5.
How metabolic age is estimated
- Lean mass = weight × (1 − body fat %).
- Your BMR from lean mass (Katch–McArdle): 370 + 21.6 × lean mass in kg.
- The average BMR for your sex, height and weight falls by 5 kcal a day per year of age (Mifflin–St Jeor). Metabolic age is the age at which that average equals your BMR.
Why scales give different numbers
Bathroom scales and apps that report metabolic age use their own, often unpublished, formulas. The method here is transparent, so you can see every number.
Lowering metabolic age
Building muscle with resistance training raises lean mass and resting calorie burn. Losing fat without losing muscle also improves the comparison.
Metabolic Age Calculator quiz: 10 questions
Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.
Quiz complete
Frequently asked questions
What is a good metabolic age?
Equal to or below your actual age.
Do I need my body fat percentage?
It makes the result meaningful. Without it the calculator estimates body fat from BMI, which is less accurate.
Why is my metabolic age higher than my age?
Usually because of lower muscle mass relative to body size.
How accurate is it?
BMR formulas have errors of about ±10% for individuals, so treat the result as a rough guide.
Does it work for athletes?
Yes, and they often get a young metabolic age because of high lean mass.
Sources
- Mifflin et al. (1990), A new predictive equation for resting energy expenditure, Am J Clin Nutr
- Deurenberg et al. (1991), Body mass index as a measure of body fatness, Br J Nutr
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