Metabolic Age Calculator

Metabolic age is the age whose typical basal metabolic rate (BMR) most closely matches your own. It starts from a real, validated number, your BMR, and then does something that isn't itself clinically standardized: compares it to typical values for other ages and reports back whichever age bracket matches best¹. The first half is established science. The second half is a popularization layered on top.

What This Calculator Measures

This calculates your BMR, then finds the age bracket whose typical BMR most closely matches your own, and reports that age bracket as your "metabolic age." It's a comparison, not a distinct biological measurement.

The Formula

BMR is calculated using the same Mifflin-St Jeor formula already used on the BMR Calculator, from your sex, age, height, and weight¹.

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5

Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

That BMR is then compared against a set of approximate typical BMR values for each age bracket. These were set for this tool, not taken from a published dataset, because no standard reference exists. "Metabolic age" is the age bracket whose typical BMR most closely matches your own, the standard approach behind the popularized version of this metric, not a distinct or more rigorous calculation.

How This Calculator Computes Your Result

Enter your sex, age, height, and weight. We calculate your BMR using Mifflin-St Jeor¹, then find which age bracket's typical BMR is closest to your own and report that as your metabolic age.

The calculator holds a set of typical BMR values across adult ages for each sex, roughly one per decade. When your BMR falls between two of those values, it reads your age along a straight line between them, so the result can land between brackets. It is rounded to a whole year. Results stay between 22 and 81, the youngest and oldest reference points, so a BMR above or below the whole range returns one of those ends.

Worked Example

Take a 40-year-old man who is 178 cm (about 5'10") and weighs 80 kg (about 176 lb). His BMR is 10 × 80 + 6.25 × 178 − 5 × 40 + 5 = 1,717.5 calories a day, shown as 1,718.

In the calculator's reference values for men, a typical BMR is 1,750 at age 30.5 and 1,700 at age 40.5. His 1,717.5 sits 65% of the way from the first to the second, so his metabolic age is 30.5 + 0.65 × 10 = 37 years, three years under his real age.

Now change only his weight. At 70 kg his BMR drops to 1,617.5 and his metabolic age rises to 57. At 90 kg his BMR is 1,817.5, above every reference value, and the result is 22. A 10 kg change in either direction moves the answer by 15 to 20 years.

What the Calculator Can't See

Mifflin-St Jeor works from total body weight, not body composition¹. Two people of the same sex, age, height and weight get the same metabolic age even if one is far more muscular. Any weight gain, fat or muscle, raises the estimated BMR and lowers your metabolic age here, and weight loss does the opposite. So a "younger" result from this calculator is not, on its own, a sign of better health, and an "older" result after losing fat is not a sign of worse health.

Why This Isn't the Same as a Real Age-Related Health Measurement

The part worth understanding clearly: BMR is driven overwhelmingly by body size and muscle mass, not by any direct marker of biological aging. In one study of 150 adults, fat-free mass explained 63% of the differences in BMR between people, fat mass 6%, and age only 2%². Someone with more muscle mass than typical for their age has a higher measured BMR, not because their cells are aging more slowly, but because muscle tissue burns more calories at rest than fat tissue does.

That's a real, useful thing to know about your body composition, but it's a different claim entirely from measuring how fast you're actually aging, which is what tools like DNA methylation-based epigenetic clocks are built to estimate, and what this comparison was never designed to do.