Your metabolic age — know it, improve it
This calculator uses the Mifflin-St Jeor formula to compute your BMR, then compares it to reference BMR values for your sex at every age from 18 to 80 (using population average heights and weights). The age whose reference BMR most closely matches yours is your estimated metabolic age. A lower metabolic age than your real age is a sign of greater lean muscle mass and a more active metabolism.
What Is Metabolic Age?
Metabolic age is a way of describing how your Basal Metabolic Rate (BMR) compares to the average BMR of people in different age groups. If your metabolism burns as many calories at rest as a typical 28-year-old, your metabolic age is 28 — regardless of your actual birthday.
The concept was popularized by body composition scales and fitness trackers. While it is not a clinical measure, it serves as a practical and motivating way to understand your metabolic health and track progress over time.
Metabolic Age vs. Chronological Age
Your chronological age is simply how many years you have been alive. Your metabolic age reflects how efficiently your body burns energy at rest. The two can differ significantly depending on your muscle mass, lifestyle, diet, sleep, and exercise habits.
How to Use This Metabolic Age Calculator
- Choose Metric or Imperial: Select the unit system you are comfortable with.
- Enter your biological sex: Required — the BMR formula differs for males and females.
- Enter your age: Your real (chronological) age in years (18–80).
- Enter height and weight: Both are required for the BMR formula.
- (Optional) Select activity level: Adds a TDEE estimate to your results.
- Read your results: Metabolic age, BMR, metabolism speed score, visual meter, and tips.
How Metabolic Age Is Calculated
Step 1 — Calculate your BMR
We use the Mifflin-St Jeor equation, considered the most accurate formula for most adults:
Male: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Female: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
Step 2 — Compare to age-group averages
Your BMR is compared to a reference table of average BMR values for each age from 18 to 80, calculated using population-average heights and weights for each age group and sex. The age whose reference BMR matches yours most closely is your metabolic age.
Step 3 — Metabolism speed score
Your BMR difference from the reference average for your actual age is normalized to produce a 0–100 metabolism speed score. A score above 50 means your metabolism is faster than average for your age group; below 50 means slower.
Key Factors That Affect Your Metabolic Age
Understanding what influences your metabolism helps you take targeted action to improve your metabolic age.
Lean Muscle Mass
Muscle tissue burns approximately 3× more calories per pound than fat tissue at rest. More muscle = higher BMR = younger metabolic age. Strength training is the most powerful lever you have.
Physical Activity Level
Regular exercise — especially resistance training and HIIT — increases BMR both during and after exercise (the "afterburn" effect). Staying active throughout the day also matters significantly.
Protein Intake
Protein has the highest thermic effect of food (TEF) at 20–30%, compared to 5–10% for carbs and 0–3% for fat. Adequate protein also preserves muscle mass, protecting your BMR as you age.
Sleep Quality
Poor or short sleep disrupts hormones like leptin, ghrelin, and cortisol, leading to muscle breakdown and increased fat storage — both of which lower BMR and raise metabolic age over time.
Age-Related Muscle Loss (Sarcopenia)
Adults naturally lose 3–8% of muscle mass per decade after age 30 if they don't actively resist it. This is the primary reason BMR declines with age — and why strength training becomes increasingly important.
Hormones & Thyroid Function
Thyroid hormones directly regulate metabolic rate. Hypothyroidism significantly slows BMR. Sex hormones (testosterone in men, estrogen in women) also influence muscle mass and resting energy expenditure.
Average BMR Reference by Age Group
These reference values are computed using the Mifflin-St Jeor formula with population-average heights and weights for each age group. Your personal BMR may differ based on your actual body composition.
| Age Group | Avg BMR — Male (kcal/day) | Avg BMR — Female (kcal/day) | Note |
|---|---|---|---|
| 18–25 | ~1,740–1,780 | ~1,390–1,420 | Peak metabolic period for most |
| 26–35 | ~1,750–1,775 | ~1,395–1,415 | Stable if muscle mass maintained |
| 36–45 | ~1,710–1,755 | ~1,370–1,400 | Gradual decline begins |
| 46–55 | ~1,650–1,710 | ~1,330–1,375 | Muscle loss accelerates without training |
| 56–65 | ~1,580–1,650 | ~1,275–1,335 | Post-menopause changes in women |
| 66–75 | ~1,490–1,580 | ~1,205–1,280 | Sarcopenia risk increases significantly |
| 76–80 | ~1,400–1,490 | ~1,120–1,210 | Activity level becomes critical |
Reference values are estimates based on population averages. Individual results vary with body composition, genetics, and lifestyle.