Find exactly how many calories your body needs every day
This BMR calculator tells you your Basal Metabolic Rate — the number of calories your body burns just to stay alive while you rest. It also shows your Total Daily Energy Expenditure (TDEE), which is what you actually burn once you factor in how active you are. Whether you want to lose weight, gain muscle, or simply eat the right amount, these two numbers are where every nutrition plan starts.
Everything is calculated right here in your browser. No data is stored, and nothing you enter is uploaded anywhere.
How to use the BMR calculator
- Enter your age in years.
- Select your sex (biological sex affects the formula).
- Enter your height in centimetres (cm).
- Enter your weight in kilograms (kg).
- Choose your activity level from the dropdown — from sedentary (desk job, little exercise) to very active (hard training most days).
- Hit Calculate. You'll see your BMR and your estimated daily calorie needs (TDEE) instantly.
Worked example
Say Maria is 34 years old, 165 cm tall, weighs 68 kg, and has a desk job with light weekend exercise (lightly active).
- BMR result: ~1,469 kcal/day
- TDEE result: ~2,021 kcal/day (BMR × 1.375)
That means Maria's body burns roughly 1,469 calories just lying still all day. To maintain her current weight with her lifestyle, she needs about 2,021 calories per day. To lose weight at a steady pace, she might aim for a modest deficit of 300–500 kcal below that.
How BMR is calculated — the Mifflin-St Jeor formula
This calculator uses the Mifflin-St Jeor equation, the formula most widely recommended by dietitians today. It was validated in a 1990 study and is considered more accurate for most adults than older equations like Harris-Benedict.
The formulas in plain words: start with your weight, add a fraction of your height, subtract a fraction of your age, then add or subtract a sex-based constant.
For women:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161For men:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5Plugging Maria's numbers in: (10 × 68) + (6.25 × 165) − (5 × 34) − 161 = 680 + 1031.25 − 170 − 161 = 1,380.25 — rounded to ~1,380 kcal for her BMR. (Small differences appear depending on rounding method used.)
Activity multipliers (to get TDEE from BMR)
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Little or no exercise, desk job | × 1.2 |
| Lightly active | Light exercise 1–3 days/week | × 1.375 |
| Moderately active | Moderate exercise 3–5 days/week | × 1.55 |
| Very active | Hard exercise 6–7 days/week | × 1.725 |
| Extra active | Very hard training or physical job | × 1.9 |
How to read your result — and what it can't tell you
Your BMR is a starting estimate, not a lab measurement. Real-world calorie burn varies based on muscle mass, hormones, sleep, body temperature, and more. Think of it as a solid baseline, not an exact number to follow to the calorie.
BMR and TDEE figures don't tell you anything about the quality of the food you eat, your nutrient balance, or medical conditions that affect metabolism (like thyroid disorders). Two people with the same BMR can have very different health outcomes depending on what they eat and how they live.
If you need to make real decisions about weight loss, muscle gain, or managing a health condition, a registered dietitian or your doctor can put these numbers in context for your specific situation. The NHS Eat Well guide is a free, evidence-based starting point for general nutrition advice.
Practical tips once you know your calorie needs
- For gradual weight loss: Aim for a daily deficit of 300–500 kcal below your TDEE. Larger cuts often backfire — your body adapts and hunger increases.
- For muscle gain: A modest surplus of 200–300 kcal above TDEE, combined with resistance training, gives your body the fuel to build without excess fat gain.
- For maintenance: Eating close to your TDEE over time keeps weight stable — small fluctuations day to day are completely normal.
- Revisit the calculator when your weight, activity level, or age changes significantly. Your calorie needs shift as your body does.
- Prioritise protein and fibre: They help you feel full and preserve muscle, which keeps your BMR higher over time.
- Move more in small ways: Non-exercise activity (walking, standing, fidgeting) can add hundreds of calories to your daily burn — choose your activity level honestly.
This calculator is for general educational purposes only. It is not medical advice. Always speak with a qualified healthcare professional before making significant changes to your diet or exercise habits, especially if you have a health condition.
Ready to see your numbers? Use the calculator above — it takes under a minute and gives you a clear, personalised starting point.