⚡ The short version
A 30-year-old man at 70 kg and 175 cm has a BMR of about 1,649 kcal a day (1,483 for a woman of the same height and weight). Multiply by activity — 1.55 for moderate exercise three to five days a week — and the daily estimate is roughly 2,556 kcal.
The calculator
How to use it
- Weight and height — measured, not remembered. The equation is sensitive to both, and old numbers are the most common source of a figure that looks wrong.
- Age — the equation subtracts 5 kcal a day for every year, because resting energy use falls slowly with age.
- Sex — the constants differ (the female term is about 166 kcal lower for the same body), so this is not a cosmetic toggle.
- Activity level — the multiplier that turns a resting figure into a daily one, and the input most people get wrong by choosing who they wish they were rather than what an average week looks like.
Worked example
The tool uses the Mifflin-St Jeor equation, currently the recommended estimate for healthy adults: men 10w + 6.25h − 5a + 5, women 10w + 6.25h − 5a − 161, with weight in kilograms, height in centimetres and age in years.
For a 30-year-old man at 70 kg and 175 cm: (10 × 70) + (6.25 × 175) − (5 × 30) + 5 = 1,649 kcal a day at complete rest. The same person as a woman would be 1,483 kcal — the two equations differ by a constant, not by a percentage.
That resting figure is not what you burn in a day. Multiply by activity: sedentary 1.2 gives 1,978 kcal, light exercise 1.375 gives 2,267, moderate 1.55 gives 2,556, very active 1.725 gives 2,844 and an athlete training hard around a physical job (1.9) gives 3,133. The same body, a range of about 1,150 kcal a day, decided entirely by movement.
What a BMR number cannot know
- Body composition. Two people at 70 kg differ in how much of that is muscle, and muscle burns more at rest than fat does. The equation only sees the total.
- Medical context. Illness, recovery, some medications and thyroid conditions move resting energy use well outside the normal range.
- Who the formula was built from. Mifflin-St Jeor was derived from a specific adult population; it is less accurate at the extremes of height, weight and age.
- Your actual week. The multiplier is a blunt average. A day of desk work and a day of hill walking are not 1.55 each.
🛠️ Related health tools
❓ Frequently asked questions
What is the difference between BMR and TDEE?
BMR is what you would burn lying still all day. TDEE (total daily energy expenditure) is BMR multiplied by an activity factor — the calories you actually use in a normal week. On the worked example here, 1,649 kcal at rest becomes about 2,556 kcal at moderate activity.
Which BMR formula does this calculator use?
Mifflin-St Jeor, the equation most often recommended for healthy adults: 10 × weight in kg, plus 6.25 × height in cm, minus 5 × age, plus 5 for men or minus 161 for women. Older Harris-Benedict equations tend to overestimate by around 5%.
How accurate is a BMR estimate?
Expect roughly ±10% against a laboratory measurement for most healthy adults, and wider at the extremes of body size or age. It is accurate enough to plan around and not accurate enough to treat as a measurement of you.
Does building muscle change my BMR?
Yes, modestly. Muscle is metabolically active at rest, so adding lean mass raises resting energy use — but the widely repeated figure of 50 extra calories per pound of muscle is far too high. Realistic changes are real and small.
Should I eat to my BMR or my TDEE?
That is a decision for you and, ideally, a clinician or dietitian — not for a calculator. This page tells you what your body uses, nothing about what you should eat. Anyone managing a health condition or disordered eating should disregard the number entirely and speak to a professional.