Your metabolic age is a health metric that compares your basal metabolic rate (BMR) to the average BMR of people your chronological age. If your metabolic age is lower than your actual age, it suggests your body is functioning more efficiently — a sign of good metabolic health and lower risk for chronic conditions like diabetes and heart disease.
This calculator estimates your metabolic age for men using the Mifflin-St Jeor equation, which is considered the most accurate BMR formula for the general population. You'll need your age, height, weight, and body fat percentage (optional but recommended for a more precise result). The tool then compares your calculated BMR to the population average for your age group, giving you a metabolic age score. Use it to track changes over time as you improve your fitness and body composition.
🧬 Your Metabolic Age
How to Use This Tool
Enter your age, height, weight, and optionally your body fat percentage. The calculator uses the Mifflin-St Jeor equation to estimate your basal metabolic rate (BMR). If you provide body fat percentage, it uses the Katch-McArdle formula for a more accurate BMR based on lean body mass. Your metabolic age is then derived by comparing your BMR to a reference BMR for a healthy 30-year-old man (70 kg, 175 cm). A metabolic age lower than your actual age indicates better metabolic efficiency.
Formula Explained
The Mifflin-St Jeor equation for men is: BMR = 10 × weight(kg) + 6.25 × height(cm) – 5 × age(y) + 5. This gives your daily calorie burn at rest. The Katch-McArdle formula (used when body fat is known) is: BMR = 370 + 21.6 × lean body mass(kg), where lean body mass = weight × (1 – body fat % / 100). The reference BMR is calculated for a 30-year-old man at 70 kg and 175 cm: 10×70 + 6.25×175 – 5×30 + 5 = 1668.75 kcal/day. Your metabolic age is then: metabolic age = 30 – (your BMR – reference BMR) / 5. The divisor 5 represents the approximate BMR change per year of age.
Worked Examples
Lean mass = 85 × (1 – 0.22) = 66.3 kg.
BMR = 370 + 21.6 × 66.3 = 1802 kcal/day.
Reference BMR = 1669 kcal/day.
Difference = 1802 – 1669 = 133 kcal/day.
Metabolic age = 30 – (133 / 5) = 30 – 26.6 ≈ 3 years. (Result: 3 — capped at 15, so metabolic age = 15.)
BMR = 10×78 + 6.25×170 – 5×60 + 5 = 780 + 1062.5 – 300 + 5 = 1547.5 kcal/day.
Difference = 1547.5 – 1669 = –121.5 kcal/day.
Metabolic age = 30 – (–121.5 / 5) = 30 + 24.3 ≈ 54 years.
Factors Affecting Accuracy
Metabolic age is an estimate, not a diagnostic. Accuracy depends on the precision of your inputs, especially body fat percentage. The Mifflin-St Jeor equation has a standard error of about 100–150 kcal/day for individuals. Factors like muscle mass, genetics, hormone levels, and recent physical activity can cause day-to-day BMR variation. For a more comprehensive health assessment, combine this metric with other indicators such as waist circumference, blood pressure, and fasting glucose. If you are tracking changes over time, always measure under similar conditions (e.g., morning, fasted, after rest).
Real-World Applications
Knowing your metabolic age can motivate lifestyle changes. A lower metabolic age is associated with higher muscle mass, lower body fat, and better cardiovascular fitness. Athletes and fitness enthusiasts use it to gauge the effectiveness of training and nutrition programs. Clinicians may use BMR and metabolic age as part of a broader metabolic syndrome risk assessment. For a deeper dive into how different activities affect your calorie burn, see our aerobics calories per 30 minutes calculator or the bear MET calculator for activity comparisons.
Frequently Asked Questions
Can my metabolic age be lower than 18? The calculator caps metabolic age at 15 years to avoid unrealistic values. A very low number simply indicates exceptional metabolic health relative to the reference.
Is metabolic age the same as biological age? No. Biological age is a broader concept that includes cellular aging, telomere length, and organ function. Metabolic age focuses solely on resting energy expenditure.
How often should I recalculate? Every 4–8 weeks is reasonable if you are actively changing your body composition through diet or exercise. For maintenance, every 3–6 months is sufficient.
Does the formula work for older men (over 70)? The Mifflin-St Jeor equation was validated in adults up to age 70. For older individuals, the accuracy may decrease due to changes in body composition and metabolic rate. Use the result as a general guide.