Metabolic Age Calculator

Getting your metabolic age takes four quick entries, plus an optional body fat percentage if you know it.

1. Pick your sex, then enter your real age in years.
2. Enter your weight and pick kilograms or pounds, then your height and pick centimetres or inches.
3. If you know your body fat percentage, enter it to see a second BMR from the Katch-McArdle formula. Leave it blank if you do not know it.
4. Press Calculate, or press Enter. Your metabolic age appears first and large, with your BMR, the average BMR for your age group and the difference between them below. Press Reset to clear the form and start over.

Metabolic age is worked out in two steps. First, your BMR is estimated with the Mifflin-St Jeor equation, the formula most dietitians use. For men it is BMR = 10 x weight in kg + 6.25 x height in cm - 5 x age + 5. For women it is the same, but with - 161 instead of + 5. BMR is the calories your body burns at complete rest in a day.

Second, your BMR is compared with published average BMR values for each age group, separately for men and women. Your metabolic age is the age whose group average matches your BMR, found by straight-line interpolation between the group midpoints at ages 21.5, 30.5, 40.5, 50.5 and 60.5. If your BMR is higher than the youngest group average, the result is younger than 21, and if it is lower than the oldest group average, the result is older than 60. The answer is rounded to whole years and kept between 18 and 80.

The average BMR table comes from published average ranges by age and sex. For men the group midpoints are 1950, 1850, 1750, 1650 and 1550 kcal a day. For women they are 1650, 1550, 1450, 1350 and 1250 kcal a day. Our BMR calculator shows the same Mifflin-St Jeor result on its own.

A 40 year old man weighs 85 kg and is 180 cm tall. Here is exactly what the calculator does.

1. Work out the BMR: 10 x 85 + 6.25 x 180 - 5 x 40 + 5 = 850 + 1125 - 200 + 5 = 1780 kcal a day.
2. Find the average BMR for men near age 40. The 36 to 45 group midpoint is 1750, and the 26 to 35 group midpoint is 1850.
3. Interpolate: 1780 sits 70 below 1850 on a 100 kcal step, so the matching age is 30.5 + 0.7 x 10 = 37.5, rounded to 38 years.

His metabolic age is 38, which is 2 years younger than his real age of 40, because his BMR of 1780 is a little above the average of 1750 for his age group. As a second check, a 35 year old woman at 65 kg and 165 cm has a BMR of 1345 kcal a day, which matches the average for women near age 51, so her metabolic age is 51. The comparison uses absolute BMR, so body size moves the answer a lot, which the next sections explain.

A metabolic age below your real age means your BMR is higher than the average for your age group. A metabolic age above your real age means it is lower. Neither one is a diagnosis. The number is a comparison against averages, and averages hide a lot of real variation.

Read it as a rough guide. A gap of a few years either way is normal, because BMR formulas predict the average for people with your measurements, and a real measured BMR can differ by 10 percent or more. A gap of 15 years or more usually says more about body size than about health, because the comparison uses your total BMR in calories, and taller and heavier people burn more at rest. Check the BMR difference the tool shows, since that is the real number behind the age.

Muscle is the biggest lever you control. Muscle burns more calories at rest than fat tissue, so two people at the same weight can have very different BMRs, and the one with more muscle scores a younger metabolic age. Strength training and enough protein support muscle, while crash dieting can cost muscle and push the number up.

Body size moves the answer too, and this is the main limit of the method. A small person has a lower absolute BMR than a large person of the same age, so the comparison can give a small person an older metabolic age even when they are perfectly healthy. Age itself lowers BMR by about 5 kcal a day per year in the Mifflin-St Jeor formula, which is why the average falls from group to group. Sleep, illness, medicines and hormones also change resting burn, and none of them are in the formula.

These three numbers answer different questions. BMR is your resting calorie burn in kcal a day, and it is the input to metabolic age. BMI is weight divided by height squared, and it says nothing about muscle or fat on its own. Metabolic age turns your BMR into an age by comparing it with group averages.

Use BMR when you plan calories, because it feeds directly into your daily needs. Use BMI only as a rough size check, and use metabolic age only as a motivational number. If you want a fuller picture, our BMI calculator and calorie calculator cover the other two, and a body composition scale or a lab test gives a real measurement where a formula only estimates.