Metabolic age calculator
Metabolic age estimates how your basal metabolic rate (BMR) — the energy your body burns at rest — compares to population averages, then reports the age whose average BMR matches yours. A lower number is generally a positive sign.
How it works
First the tool computes your BMR using the Mifflin-St Jeor equation:
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + s
where s is +5 for men and −161 for women. It then holds a same-sex reference
body fixed (about 176 cm / 78 kg for men, 163 cm / 65 kg for women) and scans
ages 15 to 80, computing the reference BMR at each age. The age whose reference
BMR is closest to your own BMR is reported as your metabolic age. Because the
formula subtracts 5 kcal per year of age, a higher BMR maps to a younger
metabolic age.
Worked example
A 30-year-old man, 178 cm and 75 kg:
BMR = 10 × 75 + 6.25 × 178 − 5 × 30 + 5 = 1717 kcal/day
Scanning the male reference body (about 176 cm / 78 kg) across ages, the closest matching reference BMR lands a few years below 30, so the tool reports a metabolic age slightly younger than his real age — a positive result indicating his resting metabolism is running above average for his demographic.
| Your BMR vs reference | Metabolic age result |
|---|---|
| Higher than your age’s average | Younger than your real age |
| Approximately average | Close to your real age |
| Lower than your age’s average | Older than your real age |
What metabolic age actually measures
Metabolic age is not a clinical measurement. Body-composition scales popularised the term as a simplified way to communicate how your resting metabolism compares to population norms. The number is useful primarily as a directional signal rather than an absolute figure. Two people with the same height, weight, and age can have meaningfully different BMRs if their muscle-to-fat ratios differ, and the Mifflin-St Jeor equation cannot see that difference — it only knows your dimensions and age.
That said, if your metabolic age comes back notably older than your real age on multiple calculators using your honest measurements, it can be a prompt to revisit two known BMR drivers: lean muscle mass and activity level. Sedentary individuals with lower muscle mass typically show higher metabolic ages because muscle is the most metabolically expensive tissue at rest.
What shifts your metabolic age over time
Resistance training is the single most effective intervention for maintaining or raising BMR as you age. Every kilogram of muscle added raises your resting calorie burn, which pushes your BMR up and, in this tool’s comparison, makes your metabolic age appear younger.
Dieting without training tends to lower BMR because significant caloric restriction causes the body to shed muscle alongside fat — a pattern known as adaptive thermogenesis. Yo-yo weight cycling over years can leave someone with a lower BMR than their height and weight alone would predict.
Ageing itself reduces the reference BMR because the formula subtracts 5 kcal per year of age. So the population average BMR for a 50-year-old is genuinely lower than for a 30-year-old of the same size, and staying above that average requires intentional effort as years pass.
This is an informational estimate only, not a clinical or diagnostic measure. All calculations run entirely in your browser.