Short answerMetabolic age compares your body with what's typical at each age. This calculator finds the age at which your body fat would be average for your BMI and sex. A 40-year-old woman, 5'5" and 150 pounds, with 32% body fat has a metabolic age of about 32, because the typical body fat at her BMI and age is about 34%.
What is metabolic age?
Your resting metabolism mostly depends on your lean mass: muscle, organs and bone. Our guide on how to speed up your metabolism covers which habits change it. As people age they tend to lose muscle and gain fat, even at the same weight. So a body with more muscle and less fat "looks younger" metabolically than an average body of the same size.
"Metabolic age" turns that into a single number. It isn't a medical measurement, and there's no official formula. Smart scales each calculate it their own way and don't publish how. This free metabolic age calculator uses a method you can check.
How this metabolic age calculator works
It uses the Deurenberg equation, a published formula that predicts typical body fat from BMI, age and sex:
Typical body fat % = 1.2 × BMI + 0.23 × age − 10.8 × (1 for men, 0 for women) − 5.4
Body fat creeps up about 0.23 percentage points a year at the same BMI. The calculator turns the formula around: it takes your actual body fat and BMI and finds the age at which that body fat would be typical. That age is your metabolic age.
Here's the worked example: a woman 5'5" (165 cm) and 150 pounds (68 kg) has a BMI of 25.0. At 40, typical body fat for her BMI is 1.2 × 25 + 0.23 × 40 − 5.4 = 33.8%. She measures 32%, which would be typical at about age 32, so her metabolic age is about 32.
Metabolic age chart
This metabolic age table shows the typical body fat at each age for two BMIs. If your body fat is below the number for your age, your metabolic age is younger than your real age.
| Age | BMI 22 | BMI 25 |
|---|---|---|
| 20 | 25.6% | 29.2% |
| 30 | 27.9% | 31.5% |
| 40 | 30.2% | 33.8% |
| 50 | 32.5% | 36.1% |
| 60 | 34.8% | 38.4% |
| 70 | 37.1% | 40.7% |
| Age | BMI 22 | BMI 25 |
|---|---|---|
| 20 | 14.8% | 18.4% |
| 30 | 17.1% | 20.7% |
| 40 | 19.4% | 23.0% |
| 50 | 21.7% | 25.3% |
| 60 | 24.0% | 27.6% |
| 70 | 26.3% | 29.9% |
Each percentage point of body fat moves metabolic age by about 4 years, so small measurement errors matter. Use the same method each time, like the same scale in the morning or the same tape-measure routine, and watch the trend rather than one reading.
How to lower your metabolic age
- Strength train two or three times a week. Muscle is the main lever, and it can be built at any age.
- Eat enough protein: around 1.2 to 1.6 g per kilogram of body weight helps you keep muscle as you age. The macro calculator shows yours.
- Move every day. Walking and daily activity add up more than a single workout.
- Lose excess fat slowly, about 1 pound a week, so you keep muscle. The weight loss simulator plans it.
- Sleep 7 or more hours; poor sleep makes holding on to muscle harder.
For your resting metabolism itself, in calories, use the BMR calculator.
Muscle, age and your metabolism
Does metabolism really slow with age? A large 2021 study in Science, which measured more than 6,000 people, found that metabolism adjusted for body size holds steady from about 20 to 60 and only declines after that. What does change for most people is body composition. Muscle tends to shrink with age, a process called sarcopenia, which speeds up in later decades, while fat tends to rise. That's exactly what the body fat equation behind this calculator captures.
The good news: muscle responds to training at any age. Strength work, enough protein and a slow pace of weight loss can lower your metabolic age over a few months. The body recomposition calculator plans calories for that, eating more on training days and less on rest days.
Metabolic age and BMR: what's the difference?
Your BMR is a number of calories: the energy your body uses at complete rest. Metabolic age is a comparison: how your body composition stacks up against what's typical at different ages. Two people with the same BMR can have different metabolic ages if one carries more muscle and the other more fat. For your full daily calorie needs, BMR plus everything you do, use the TDEE calculator.
Why your smart scale shows a different number
Bathroom scales estimate body fat by sending a small current through your feet, and the reading changes with hydration, meals and even the time of day. They then plug it into their own private metabolic age formula. Two scales can disagree by years, and so can a scale and this metabolic age calculator online. That's fine: pick one method and track the direction it moves.
Metabolic age FAQ
What is metabolic age?
An estimate of how your body compares with what's typical at different ages. A metabolic age below your real age usually means more muscle and less fat than average for your size.
How is metabolic age calculated?
There's no single standard. Smart scales each use their own formula. This calculator finds the age at which your body fat percentage would be typical for your BMI and sex, using a published equation.
How can I lower my metabolic age?
Build or keep muscle with strength training two or three times a week, eat enough protein, stay active every day and lose excess body fat slowly.
Sources
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr, 1991;65(2):105–114.
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, 1984.
- Pontzer H, et al. Daily energy expenditure through the human life course. Science, 2021.
- Volpi E, Nazemi R, Fujita S. Muscle tissue changes with aging. Curr Opin Clin Nutr Metab Care, 2004;7(4):405–410.
- McArdle WD, Katch FI, Katch VL. Exercise Physiology (Katch-McArdle resting metabolic rate).