Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep you alive — powering your heart, brain, breathing and other organs. It is the largest part of most people daily energy use.

How are my daily calorie needs calculated?

This tool uses the Mifflin-St Jeor equation to estimate BMR from your age, gender, weight and height, then multiplies it by an activity factor (1.2 to 1.9) to estimate the calories you burn in a typical day, known as your maintenance calories.

How many calories should I eat to lose weight?

A common starting point is a deficit of about 500 calories per day below maintenance, which roughly targets losing about half a kilo (one pound) per week. This is only an estimate — speak to a doctor or dietitian before making big changes.

BMR & Calorie Calculator — Mifflin-St Jeor

Estimate your Basal Metabolic Rate and daily calorie needs with the trusted Mifflin-St Jeor equation. Enter your details to see calories burned at rest, your maintenance level, and targets for gentle weight loss or gain — all worked out privately in your browser.

How to use this calculator

Gender — select male or female (the equation uses a small sex-based adjustment).
Age, weight and height — enter your age in years, weight in kilograms and height in centimetres.
Activity level — pick the option that best matches a typical week, from sedentary to very active.
Read your BMR, maintenance calories, and the weight-loss and weight-gain targets — everything updates instantly as you change a value.

Nothing is submitted or saved: your figures never leave your device, so you can check them privately.

What is BMR and how is it calculated?

Your Basal Metabolic Rate is the energy your body burns while completely at rest — keeping your heart beating, your lungs working and your cells running. It usually accounts for 60–70% of the calories most people use each day. This tool uses the Mifflin-St Jeor equation, widely regarded as the most accurate predictive formula for healthy adults:

Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

From BMR to daily calories

BMR alone assumes you do nothing all day, so we multiply it by an activity factor to estimate your Total Daily Energy Expenditure — the calories you actually burn. The factors are 1.2 (sedentary), 1.375 (light), 1.55 (moderate), 1.725 (active) and 1.9 (very active). The result is your maintenance calories: eat about that many to keep your weight steady. To lose weight gently, the calculator shows maintenance minus 500 calories a day; to gain, it shows maintenance plus 500. Roughly speaking, a 500-calorie daily change targets about half a kilogram (one pound) per week.

Health note: These numbers are general estimates and are not medical advice. Real energy needs depend on muscle mass, genetics, hormones, health conditions and more. Very low calorie intakes can be harmful. Always consult a qualified doctor or registered dietitian before changing your diet, especially if you are pregnant, unwell or under 18.

Is it private?

Yes. Every calculation runs entirely in your browser using plain JavaScript. Your age, weight, height and activity level are never uploaded, logged or sent to any server — there is no account, no tracking of your inputs, and nothing to delete.

Frequently asked questions

Which activity level should I choose?

Be honest and lean conservative. "Sedentary" suits a desk job with little exercise; "moderate" suits a few solid workouts a week; "very active" is for hard daily training or heavy physical work. Most people overestimate, so if unsure, pick the lower option.

How do I convert pounds and feet to kg and cm?

Divide your weight in pounds by 2.205 to get kilograms. Multiply your height in inches by 2.54 to get centimetres (so 5 ft 9 in = 69 in ≈ 175 cm).

Is this accurate for me?

The Mifflin-St Jeor equation is accurate on average for healthy adults but cannot account for your exact body composition or health. Treat the result as a sensible starting estimate, then adjust based on real-world results and professional advice.