Find your basal metabolic rate — the calories your body burns at rest — with the Mifflin-St Jeor equation, then see your total daily calorie needs at five activity levels from sedentary to extra active.
BMR Calculator
How the BMR Calculator Works
Your basal metabolic rate (BMR) is the number of calories your body burns in 24 hours at complete rest — the energy spent keeping your heart beating, lungs breathing, body warm and cells repaired, before a single step is counted. It is the foundation number behind almost every calorie plan: dietitians start from BMR, anyone comparing “how much should I eat?” needs it, and it explains why two people of different sizes can eat very differently and both maintain their weight.
The calculator uses the Mifflin-St Jeor equation, developed in 1990 and still the formula most health organisations recommend for estimating BMR. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161. Each input has a job: weight and height capture body size, age captures the gradual slowing of metabolism as we get older, and the final constant adjusts for average sex differences in lean mass.
On its own BMR understates real life, because nobody lies still all day. So this calculator also multiplies your BMR by five standard activity factors to show your total daily energy expenditure (TDEE) at each level: sedentary ×1.2, lightly active ×1.375, moderately active ×1.55, very active ×1.725 and extra active ×1.9. The five-row table lets you see exactly how much daily movement is worth in calorie terms — often several hundred calories between neighbouring rows.
How to Use This Calculator
- Enter your age in years.
- Select male or female — the equation uses a different constant for each.
- Add your height in centimetres and your weight in kilograms.
- Press Calculate to see your BMR as the headline result.
- Read down the activity table and find the row that matches your normal week; that figure is your estimated daily calorie burn and the right starting point for any eating plan.
Example
A 30-year-old man, 175 cm tall and 70 kg: BMR = (10 × 70) + (6.25 × 175) − (5 × 30) + 5 = 1,648.75 calories a day. His TDEE table reads: sedentary 1,978.50, lightly active 2,267.03, moderately active 2,555.56, very active 2,844.09 and extra active 3,132.63 calories a day.
A second example: a 45-year-old woman, 165 cm and 60 kg, has a BMR of (10 × 60) + (6.25 × 165) − (5 × 45) − 161 = 1,245.25 calories. At a moderately active lifestyle (×1.55) she burns about 1,930 calories a day — noticeably less than the first example, which is exactly why personalised numbers beat generic diet-book figures.
Understanding Your Result
BMR typically accounts for 60–70% of everything you burn; the rest is movement and the small cost of digesting food. That is why the activity table spans such a wide range — the same body can need 1,980 or 3,130 calories depending on how it spends its days. For weight maintenance, eat around your activity row. To lose or gain, adjust from that row (our Calorie Calculator turns these numbers into ready-made targets).
Estimates have limits. Mifflin-St Jeor is usually within about 10% for people near average body composition, but it cannot see muscle mass: two people with identical stats can differ if one is muscular and the other is not, because muscle burns more at rest. Illness, fever, thyroid conditions, pregnancy and some medicines also shift real metabolic rate in ways no formula captures. Treat BMR as a well-founded estimate and a planning anchor — if your weight trend disagrees with it over several weeks, trust the trend and adjust. Anyone managing a medical condition should get personalised advice from a clinician rather than relying on a general calculator.
The activity table also hides one everyday variable: NEAT, the energy burned by non-exercise movement — standing, walking around the office, stairs, housework, even fidgeting. Two people in the same job and gym routine can differ by several hundred calories a day purely through NEAT, which is why step counts and daily movement habits often explain plateaus better than a formula can.
BMR Calculator FAQs
What is the difference between BMR and TDEE?
BMR is what you burn at complete rest. TDEE (total daily energy expenditure) is BMR multiplied by an activity factor, so it includes work, walking, exercise and daily life — it is the better number for planning what to eat.
Does BMR really drop with age?
Yes, gradually — the formula subtracts 5 calories for every year of age, reflecting the slow loss of muscle mass over adulthood. Staying active and keeping muscle through resistance training softens the decline.
Why is women’s BMR calculated differently?
On average, women carry a higher proportion of body fat and less muscle than men of the same size, and fat tissue burns fewer calories at rest than muscle. The −161 constant reflects that average difference.
Can I eat exactly my BMR to lose weight?
You would lose weight, since your total burn is higher than BMR, but eating at BMR level can feel very restrictive and may undershoot nutrients. A moderate deficit below your TDEE is safer and more sustainable for most people.
How accurate is the Mifflin-St Jeor equation?
It is considered the most accurate of the common predictive formulas, typically within about 10% of measured values for most adults. Direct measurement requires laboratory equipment, so an estimate like this is the practical option.
Related calculators: Calorie Calculator, BMI Calculator, Body Fat Calculator.