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Metabolic Age Calculator
Use this free metabolic age calculator to compare your metabolism with the average for your age. Enter your age, sex, weight, height, and activity level, and it works out your basal metabolic rate (BMR) with the Mifflin-St Jeor equation, then estimates your metabolic age by matching your BMR against the average BMR for each age group — plus your daily calorie needs and three practical tips.
How it works
Your body burns calories all the time, even when you are lying still doing nothing. That resting burn is your basal metabolic rate, or BMR — the energy your body needs to keep your heart beating, your lungs working, your brain running, and your body temperature steady. Everything else you burn in a day, from walking to the kitchen to an hour at the gym, sits on top of BMR. Metabolic age takes your BMR and asks a simple question: at what age does the average person have a BMR like yours?
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
The calculator first works out your BMR with the Mifflin-St Jeor equation, the formula most dietitians use because it has held up best in studies. It needs four things: your sex, your weight in kilograms, your height in centimeters, and your age. The 10 × weight term is the biggest, because a heavier body needs more energy to maintain. The 6.25 × height term adds a little for taller frames. The −5 × age term is the reason BMR falls as you get older — roughly 5 fewer calories a day for every year of age, mostly because muscle slowly gives way to fat. Men get +5 and women −161 at the end, reflecting the average difference in body composition between the sexes. The result is accurate to about 10 percent for most people, though it can be off for very muscular or very lean bodies, because the formula sees weight, not what the weight is made of.
Next comes the metabolic age step. The calculator builds an average BMR curve: for each age from 20 to 75, it works out the average BMR for someone of your sex and height, using approximate average body weights for each age group. Your BMR is then matched against that curve, and the age where the curve equals your BMR is your estimated metabolic age. If your BMR is higher than the average for your age — usually because you carry more muscle or move more — the match lands at a younger age. If it is lower, the match lands older. Because the curve is built from your own height and sex, the comparison is apples to apples.
Your activity level then turns BMR into daily calorie needs, called total daily energy expenditure (TDEE). The calculator multiplies your BMR by an activity factor: 1.2 for a sedentary life, 1.375 for light activity, 1.55 for moderate exercise three to five days a week, 1.725 for hard exercise most days, and 1.9 for a physical job or twice-a-day training.
Three things move metabolic age most. Muscle is first: muscle tissue burns roughly three times as many calories at rest as fat tissue, so two people at the same weight can have very different BMRs. Strength training two or three times a week is the most reliable way to protect muscle as you age. Protein is second, because it both supports muscle and costs more energy to digest than carbohydrate or fat. And sleep is third — short sleep disrupts the hormones that regulate hunger and muscle repair.
Worked example
A 30-year-old man weighs 180 lb, is 5 feet 10 inches tall, and exercises moderately three to five days a week. What are his BMR, his daily calorie needs, and his metabolic age?
Step 1: Convert to metric — 180 lb = 81.65 kg, and 5'10" = 70 inches = 177.8 cm.
Step 2: Apply Mifflin-St Jeor for a man — BMR = 10 × 81.65 + 6.25 × 177.8 − 5 × 30 + 5 = 816.5 + 1,111.25 − 150 + 5 = 1,783 kcal/day.
Step 3: Daily needs — 1,783 × 1.55 (moderately active) = 2,763 kcal/day.
Step 4: Match against the average BMR curve — the average BMR for his profile is about 1,799 kcal at age 25 and about 1,767 kcal at age 35, so his 1,783 kcal matches the curve at age 30.
Step 5: Metabolic age ≈ 30 years — exactly his actual age, so his metabolism is right on average for his age.
Enter the same numbers in the calculator and it gives exactly the same result: BMR 1,783 kcal/day, about 2,763 kcal/day for daily needs, and a metabolic age of about 30. Try changing the activity level to sedentary and the daily needs drop to about 2,139 kcal, or change the sex to female with the same numbers and the BMR falls to 1,617 kcal/day, because the women's formula ends in −161 instead of +5.
FAQ
What is metabolic age?
Metabolic age compares your basal metabolic rate (BMR) with the average BMR for each age group. If your BMR is higher than the average for your age, your metabolic age comes out younger, and if it is lower, it comes out older. It is an estimate based on a formula, not a medical measurement, and it says nothing about your health on its own.
How is metabolic age calculated?
First your BMR is calculated with the Mifflin-St Jeor equation from your sex, weight, height, and age. Then that BMR is compared with the average BMR for each age group, using the same sex and height and approximate average weights for each age group. The age whose average BMR matches yours is your estimated metabolic age.
What is the Mifflin-St Jeor equation?
The Mifflin-St Jeor equation estimates basal metabolic rate from sex, weight in kilograms, height in centimeters, and age: for men, BMR = 10 x weight + 6.25 x height - 5 x age + 5; for women, the same formula ends in -161 instead of +5. It is the most widely used BMR formula and is accurate to about 10 percent for most people.
Is a metabolic age younger than my real age good?
A younger metabolic age usually means you burn more calories at rest than the average person your age, which often goes with more muscle and more activity. But it is only an estimate from a formula, and a single number cannot tell you whether you are healthy. Muscle mass, sleep, diet, and medical history all matter far more than this one figure.
How can I lower my metabolic age?
The most reliable way is to build and keep muscle with strength training two or three times a week, since muscle burns more calories at rest than fat. Eating enough protein, staying active every day, sleeping 7 to 9 hours, and keeping a healthy weight all help too. Changes take weeks to show up, so think in months rather than days.