Metabolic Age Calculator
This page estimates your resting calories (BMR) with the published Mifflin-St Jeor equation and your daily calories (TDEE) with standard activity multipliers. "Metabolic age" has no agreed scientific definition: scales and apps use their own private formulas. We only show an age comparison if you enter a measured resting metabolic rate, and we label it as our own unvalidated conversion.
Before you start
Method : BMR from the published Mifflin-St Jeor equation; daily calories from conventional activity factors; optional age comparison is our own conversion.
Validation : BMR formula checked against hand calculations. The equation is typically within about 10% for many adults, not all. The age comparison is unvalidated.
Review : not reviewed by a qualified clinician. Educational only — not a diagnosis or a medical test.
Not suitable for children, pregnancy, or medical nutrition planning — ask a dietitian.
Your answers stay in this browser tab; nothing is sent or stored.
Only from a breath-gas (indirect calorimetry) test. Don't copy a scale's or app's estimate.
Enter your details to estimate BMR and daily calories.
How to Use This Calculator
- Choose units and enter age, sex, weight and height.
- Pick your activity level.
- Optionally enter a measured RMR from a breath test (indirect calorimetry).
- Press Calculate.
Methodology & assumptions
BMR (published): men = 10 × kg + 6.25 × cm − 5 × age + 5; women = 10 × kg + 6.25 × cm − 5 × age − 161 (kcal/day). Derived from 498 healthy adults aged 19–78, normal-weight and obese.
TDEE (convention): BMR × activity factor (1.2 to 1.9).
Equation-equivalent age (our own, unvalidated): if you enter a measured RMR, we solve the same equation for the age at which it would predict that RMR: age = (10 × kg + 6.25 × cm + 5 or −161 − RMR) ÷ 5. Every 50 kcal/day moves this by 10 years, so ordinary measurement error swings it a lot.
Worked examples
Man, 30 y, 70 kg, 175 cm, sedentary: BMR = 700 + 1093.75 − 150 + 5 = 1,649 kcal/day; TDEE = 1,648.75 × 1.2 = 1,979 kcal/day.
Woman, 40 y, 60 kg, 165 cm, measured RMR 1,320: BMR = 600 + 1031.25 − 200 − 161 = 1,270 kcal/day. Equation-equivalent age = (600 + 1031.25 − 161 − 1320) ÷ 5 = 30.05, shown as 30 years (unvalidated).
Understanding your result
BMR is an estimate for a typical person of your size; your real value can easily be 10% or more higher or lower. It is less reliable for people outside 19–78, athletes with a lot of muscle, pregnancy, and some medical conditions. The equation-equivalent age is not a health measure and has never been tested against outcomes.
Sources & further reading
- Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 1990;51(2):241-247.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105(5):775-789.
The activity multipliers and the equation-equivalent age are conventions, not results from these papers.
Frequently Asked Questions
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