How Many Calories Do You Need? BMR and TDEE

"How many calories should I eat?" has a different answer for everyone, but it starts with two numbers that you can estimate yourself: your BMR and your TDEE. This guide explains what they are, how they're calculated, and how to use them sensibly.

This is general information, not medical or dietary advice. Calorie needs vary, and anyone with a health condition, who is pregnant, or who is planning a significant change in eating should speak to a doctor or registered dietitian first.

What BMR is

Basal Metabolic Rate is the energy your body uses just to stay alive at complete rest: breathing, circulation, keeping organs working and maintaining body temperature. For most people it makes up the biggest share of the calories they burn in a day.

What TDEE is

Total Daily Energy Expenditure is BMR plus everything else: walking around, exercise, work, digesting food and even fidgeting. It's your estimate of the calories you burn in a whole day, and so roughly the amount you'd eat to keep your weight steady, your maintenance calories.

How BMR is estimated

One of the most widely used formulas is Mifflin-St Jeor, which uses weight, height, age and sex:

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

A worked example for a 30-year-old man who weighs 80 kg and is 180 cm tall: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 800 + 1,125 − 150 + 5 = 1,780 calories per day at rest.

And for a 30-year-old woman who weighs 65 kg and is 165 cm tall: 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = about 1,370 calories per day.

From BMR to TDEE: the activity multiplier

TDEE is BMR multiplied by a factor that reflects how active you are:

Activity level	Multiplier	Typical description
Sedentary	1.2	Little or no exercise, desk job
Light	1.375	Light exercise 1 to 3 days a week
Moderate	1.55	Moderate exercise 3 to 5 days a week
Active	1.725	Hard exercise 6 to 7 days a week
Very active	1.9	Very hard exercise or a physical job

For the man above: moderate activity gives 1,780 × 1.55 = about 2,759 calories to maintain his weight. For the woman, light activity gives 1,370 × 1.375 = about 1,884 calories.

Be honest when you choose the activity level. People tend to overestimate it, and a slightly lower choice is usually closer to the truth.

Using the number for weight loss or gain

Your maintenance figure is the reference point:

• Eat less than maintenance and, over time, your weight tends to fall.
• Eat more than maintenance and it tends to rise.

A common rule of thumb is that about 3,500 calories equals roughly 0.45 kg (1 lb) of body fat, so a daily gap of 500 calories works out to around 0.45 kg a week. Treat that as a rough guide only: real results vary, because your metabolism adjusts and the estimate itself is approximate.

The Calorie Calculator does this for you. It returns your BMR, your maintenance calories, and targets for mild and standard weight loss (250 and 500 calories below maintenance) and mild and standard weight gain (250 and 500 above). For the woman in our example, a mild deficit would be about 1,634 calories and a 500-calorie deficit about 1,384.

Important cautions

• These are estimates. Formulas are based on averages. Your real needs can differ by several hundred calories a day.
• Don't cut too far. Very low intakes are hard to sustain, can leave you short of nutrients and aren't safe without supervision. Seek advice before eating much less than your maintenance figure suggests.
• Quality matters, not just quantity. The same calories from whole foods, protein and fibre feel very different from the same number in sugary snacks.
• Your needs change. Weight, age and activity all shift your BMR and TDEE, so recalculate every so often.
• Special situations differ. Pregnancy, breastfeeding, growing teenagers, medical conditions and some medications change energy needs, and general calculators don't account for them.

A practical way to use it

1. Estimate your maintenance calories with a calculator.
2. Track what you actually eat for a week or two and see how your weight responds.
3. Adjust in small steps, 100 to 250 calories at a time, and give each change a couple of weeks.
4. Pair it with the basics: regular movement, enough sleep and mostly unprocessed food.
5. Check in with a professional if you want a plan for a specific goal.

How it fits with BMI

BMI gives a snapshot of weight relative to height; BMR and TDEE estimate energy use. They answer different questions. Our post on what BMI does and doesn't tell you covers the first, and you can calculate your BMR on its own with the BMR Calculator or check your BMI with the BMI Calculator.

The short version

BMR is what your body burns at rest; TDEE is what it burns in a day once activity is included. Estimate both with a standard formula, treat the results as a starting point rather than a precise figure, make changes gradually, and get professional advice before making big changes or if you have any health concerns.