Find out how your metabolism compares to the average person your age. Your metabolic age is the age at which the typical person burns the same number of calories at rest as you do — driven almost entirely by your muscle mass.
Metabolic age compares your Basal Metabolic Rate (BMR) — the number of calories your body burns at complete rest — to the average BMR for people of your sex and height at different ages. If your BMR matches what a typical 35-year-old of your height burns, your metabolic age is 35, regardless of how old you actually are.
It's a more meaningful number than BMR alone because it contextualises your calorie burn against what's normal for your age group. A higher-than-average BMR for your age means a younger metabolic age; a lower-than-average BMR means an older one.
BMR is primarily determined by lean muscle mass. Muscle burns approximately 3× more calories at rest than fat tissue. This means two people of identical weight, height and age can have metabolic ages years apart — depending entirely on how much of that weight is muscle versus fat. Resistance training is the single most powerful lever for improving metabolic age.
This calculator uses the Mifflin-St Jeor equation — the most validated formula for estimating BMR from height, weight, age and sex:
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
Your result is then compared to the expected BMR for people of your sex and height at each age, using population-average body weight data for each age group. The age at which the expected BMR most closely matches yours is your metabolic age.
Any BMR-based metabolic age estimate is an approximation. Without direct measurement of lean muscle mass (via DEXA scan or bioelectrical impedance), the calculation uses your total body weight. Two people with the same total weight but different body compositions will have the same calculated BMR — but the more muscular person has genuinely better metabolic health. Body fat % is the missing variable in web-based calculations.
| Factor | Effect on metabolic age | Modifiable? |
|---|---|---|
| Muscle mass | Each kg of muscle adds ~13 kcal/day to BMR | Yes — resistance training |
| Body fat % | Higher fat % = lower BMR per kg of total weight | Yes — training + diet |
| Sarcopenia | 3–8% muscle loss per decade after 30; accelerates after 60 | Partially — exercise slows it significantly |
| Thyroid function | Hypothyroidism reduces BMR by 20–40% | With medical treatment |
| Sleep quality | Chronic sleep deprivation impairs muscle protein synthesis | Yes |
| Protein intake | Inadequate protein accelerates age-related muscle loss | Yes — 1.2–1.6g/kg/day for over-50s |
| Sex hormones | Testosterone and oestrogen both support lean mass; decline with age | Partially — HRT, exercise, sleep |
Ideally, your metabolic age equals or is younger than your actual age. The gap matters more than the absolute number — being 5 years metabolically younger than your chronological age suggests you have above-average muscle mass or lean body composition for your age group.
Don't be discouraged if your metabolic age is older than expected. This calculator compares you to the average person your age — who in most countries is overweight and carries above-average total body mass. Someone lean and healthy may calculate a higher metabolic age simply because their total weight (and therefore BMR) is lower than the heavier population average. Context matters.
Adding muscle mass directly raises BMR. Studies show people can meaningfully increase muscle mass at any age — including those in their 60s, 70s and beyond. Even 2–3 resistance training sessions per week produces measurable BMR increases within 8–12 weeks. See our strength training over 50 guide and resistance training over 40 guide.
Protein is the raw material for muscle. For people over 50, 1.2–1.6g per kg of bodyweight per day is recommended by sarcopenia researchers — substantially above the standard dietary guidelines. Spreading intake across 3–4 meals (30–40g per meal) maximises muscle protein synthesis. Full details in our protein intake over 50 guide.
Very low-calorie dieting is one of the fastest ways to age your metabolism. Severe deficits trigger adaptive thermogenesis — your body reduces BMR to conserve energy — and accelerate muscle catabolism. Modest deficits (300–500 kcal/day) with high protein intake and resistance training preserve muscle while losing fat.
Growth hormone — critical for muscle repair and maintenance — is primarily secreted during deep sleep. Chronic sleep deprivation impairs muscle protein synthesis and increases cortisol, which promotes muscle breakdown. 7–9 hours is the target for adults of any age. See our sleep and memory guide.
Testosterone in men and oestrogen in women both support lean muscle mass. Their decline with age is one mechanism behind the worsening metabolic age seen in older adults. Exercise partially compensates for hormonal decline, and HRT is worth discussing with a doctor for women in perimenopause experiencing significant muscle loss.
| Decade | What typically happens | Impact on metabolic age |
|---|---|---|
| 20s | Peak muscle mass, high hormone levels, fast recovery | Metabolic age typically ≤ actual age |
| 30s | Gradual muscle loss begins (~1% per year without training), weight often rises | Divergence begins for sedentary people |
| 40s | Muscle loss accelerates slightly, fat tends to accumulate centrally | Sedentary adults often 5–10 years older metabolically |
| 50s | Hormonal shifts (testosterone decline, perimenopause) accelerate muscle loss | Gap widens significantly without training |
| 60s+ | Sarcopenia becomes clinically relevant; muscle loss ~1–2% per year | Active adults can maintain near-actual-age; sedentary adults may be 15–20 years older |