Last updated: 3 August 2026
Reviewed by Jordan Makin, FA Level 2 Football Coach
Basal Metabolic Rate
BMR vs BMI — two easily confused numbers
Despite the similar-sounding names, BMR and BMI measure completely different things. BMI is a weight-to-height ratio used to categorise body weight (underweight, healthy, overweight). BMR is an estimate of the calories your body burns at complete rest — it has nothing to do with categorising your weight, and a "high" or "low" BMR isn't good or bad on its own the way BMI categories are framed. If you want your BMI, use the BMI Calculator instead — the two are unrelated calculations that happen to get mixed up because of the acronym similarity.
How your BMR compares to average
There's no single "correct" BMR — it depends heavily on your age, height, weight and sex — but as a rough population reference point, the average adult male's BMR is approximately 1,650-1,700 kcal/day, and the average adult female's is approximately 1,400-1,450 kcal/day. These are population averages, not targets — your own number above is specific to your actual stats and is the more useful figure for your own planning.
What affects BMR beyond the formula
The Mifflin-St Jeor formula above uses age, height, weight and sex because those are the strongest predictors of BMR — but several other factors genuinely affect your actual metabolic rate that no formula captures:
- Muscle mass — more muscle tissue burns more calories at rest than fat tissue, which is why the Katch-McArdle formula (used on this site's TDEE Calculator when you know your body fat %) can be more accurate for muscular individuals.
- Thyroid and hormonal function — conditions like hypothyroidism or hyperthyroidism can significantly raise or lower metabolic rate independent of body composition. If your real-world calorie needs consistently don't match your calculated BMR, this is worth discussing with a doctor.
- Environmental temperature — the body burns slightly more energy maintaining core temperature in very cold conditions.
- Age-related muscle loss — BMR naturally trends downward with age partly because muscle mass tends to decline without active resistance training to offset it.
Top picks compared
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| Option | RENPHO Smart Food Scale | Tracks macros and calories for meals. Essential for dialing in your BMR-based nutrition targets. | Check price → |
| Option | Fitbit Charge 6 Activity Tracker | Tracks daily calories burned and active minutes. Shows how your actual burn compares to calculated BMR. | Check price → |
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Frequently asked questions
BMR vs TDEE?
BMR is at-rest burn; TDEE adds your daily activity. To lose weight you eat below TDEE, not below BMR.
Should I ever eat below my BMR?
Most nutrition guidance advises against eating below your BMR for extended periods, since this is the minimum energy your body needs just to maintain basic functions — sustained intake below this level can affect metabolism, muscle mass and overall health over time.
Why is my BMR different from a friend with the same height and weight?
Age, sex and body composition (muscle vs fat ratio) all affect BMR independently of height and weight — someone with more muscle mass will typically have a higher BMR than someone the same height/weight with more body fat, since muscle tissue is more metabolically active at rest.