How Many Calories Do I Burn a Day? (BMR and TDEE Explained)

Your body is burning calories right now, even as you read this. Not from working out. Not from walking. Just from existing.

That constant background burn has a name: your Basal Metabolic Rate, or BMR. And once you know roughly what yours is, a lot of nutrition and weight loss advice starts to make much more sense.

What is BMR?

BMR stands for Basal Metabolic Rate. It is the number of calories your body needs to stay alive at complete rest. Think of it as the energy cost of running your organs: your heart pumping blood, your lungs breathing, your kidneys filtering, your liver processing nutrients, your brain staying active, and your body keeping a stable temperature.

If you did absolutely nothing for 24 hours, no movement, no food, just lying still, your body would still burn your BMR amount of calories just to keep you alive.

For most adults, BMR accounts for around 60 to 75% of total daily calorie burn. That is more than exercise, more than digestion, more than any other single factor. Which means your BMR is not a small detail you can ignore. It is the foundation everything else is built on.

What is TDEE?

TDEE stands for Total Daily Energy Expenditure. It is your total calorie burn across a full day, covering your BMR plus everything else: walking, cooking, commuting, working out, fidgeting, and even digesting food (which uses roughly 8 to 10% of your daily calories on its own).

BMR is your floor. TDEE is your real daily number. And your TDEE is what you need to match, exceed, or stay below depending on your goal.

To lose weight, you eat below your TDEE. To gain muscle, you eat slightly above it. To maintain, you match it. That simple framework explains almost all calorie-based nutrition advice.

How to calculate your BMR

The most widely used formula for estimating BMR is the Mifflin-St Jeor equation. It was developed in 1990 and uses your weight, height, age and sex to produce a reliable estimate. Research has consistently found it to be one of the more accurate prediction equations for resting metabolic rate in healthy adults. (PubMed)

Mifflin-St Jeor formula

For men:

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5

For women:

BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161

Example: man

A 30-year-old man who is 180 cm tall and weighs 80 kg:

BMR = (10 x 80) + (6.25 x 180) - (5 x 30) + 5
BMR = 800 + 1,125 - 150 + 5
BMR = 1,780 calories/day

His body burns approximately 1,780 calories per day at rest.

Example: woman

A 35-year-old woman who is 165 cm tall and weighs 65 kg:

BMR = (10 x 65) + (6.25 x 165) - (5 x 35) - 161
BMR = 650 + 1,031 - 175 - 161
BMR = 1,345 calories/day

Her body burns approximately 1,345 calories per day at rest.

Skip the maths entirely with our free BMR Calculator, which works out both your BMR and TDEE in seconds.

Activity multipliers: from BMR to TDEE

Once you have your BMR, multiply it by an activity factor to estimate how many calories you actually burn each day. This step is where most people underestimate themselves, or overestimate, so read the descriptions carefully before choosing.

Using the example above: If the 30-year-old man (BMR 1,780) is moderately active:

TDEE = 1,780 x 1.55 = 2,759 calories/day

He needs roughly 2,759 calories per day to maintain his current weight. To lose weight at a steady pace, he could aim for around 2,250 to 2,459 calories per day.

One honest tip: if you are unsure which activity level to pick, most people slightly overestimate how active they are. When in doubt, start one level lower and adjust based on your results over 2 to 3 weeks.

What affects your BMR?

Two people of the same weight can have meaningfully different BMRs. Here is what drives those differences.

Body composition

Muscle tissue burns more calories at rest than fat tissue. People with higher muscle mass have a higher BMR than someone of the same body weight but with more fat. This is why strength training has a long-term effect on how many calories you burn, even on days you do not work out.

Age

BMR gradually decreases with age. From around 30 onwards, most people lose a small amount of muscle mass each decade unless they actively train against it. Less muscle means a slightly lower resting burn. This is one reason it gets harder to maintain weight as you get older, even if your eating habits do not change much.

Sex

Men typically have higher BMRs than women of the same height and weight. This is mostly because men on average carry more muscle mass and less body fat, not because of any fundamental metabolic difference.

Height and body size

Larger bodies have more cells to maintain, more surface area to regulate temperature, and more organ mass. All of that adds up to a higher BMR.

Genetics

Some people do naturally burn slightly more or fewer calories at rest. This is real, but the effect is smaller than most people assume. Studies suggest genetic variation accounts for roughly 5 to 10% of the difference in BMR between individuals.

Thyroid function

Thyroid hormones regulate how fast your cells produce energy. An underactive thyroid (hypothyroidism) can slow BMR meaningfully. If you feel persistently cold, fatigued, or find weight loss unusually difficult despite eating in a deficit, it is worth speaking with a doctor to rule out thyroid issues.

Diet history

Extended periods of very low calorie intake can cause your BMR to decrease. Your body adapts to less food by reducing how much energy it burns. This is sometimes called metabolic adaptation, and it is one reason aggressive crash diets tend to backfire over time. A moderate deficit is more sustainable and puts less downward pressure on your metabolic rate.

How to use your BMR number

Once you have your estimated TDEE, here is how to apply it to your goal:

• Lose weight: Eat 300 to 500 calories below your TDEE per day. This produces roughly 0.3 to 0.5 kg of weight loss per week, which is a sustainable pace for most people.
• Gain muscle: Eat 200 to 350 calories above your TDEE per day, combined with consistent strength training. A small surplus reduces unnecessary fat gain while still supporting muscle growth.
• Maintain weight: Eat roughly at your TDEE. Your weight will naturally fluctuate a few pounds week to week, so watch the trend over 2 to 3 weeks rather than reacting to daily changes on the scale.

Your TDEE is an estimate, not a guarantee. Track your weight trend over 2 to 3 weeks. If nothing is changing when you expect it to, your actual burn is likely slightly different from the calculator's estimate. Adjust your intake by 100 to 200 calories in the right direction and check again.

For a complete picture of how to set your calorie target based on your goal, see our article on how many calories you should eat per day.

Common BMR and metabolism myths

Myth: Eating small meals frequently boosts metabolism

The number of meals you eat does not meaningfully change your total daily calorie burn. What matters is total intake, total protein, and your overall energy balance across the day. Meal frequency is a personal preference, not a metabolic lever.

Myth: Some foods "burn fat" by boosting metabolism

Certain foods like green tea or chilli have a tiny thermogenic effect, but it is far too small to produce noticeable fat loss on its own. The effect is measured in single-digit calories per day in most studies.

Myth: A slow metabolism is why most people gain weight

Research comparing people who gain weight easily to those who do not has generally found only small differences in BMR after adjusting for body composition. In most cases, weight gain comes down to eating habits and activity levels more than a meaningfully slower metabolic rate.

Frequently asked questions

Is BMR the same as metabolism?

Your metabolism covers all the chemical processes happening in your body at any given moment. BMR is one specific measurement within that: the energy cost of staying alive at rest. When people say someone has a fast metabolism, they usually mean a high BMR.

How accurate is the Mifflin-St Jeor equation?

Research suggests it is one of the more reliable formulas for the general adult population. In practice, it may be off by around 5 to 10% for some individuals, particularly athletes with very high muscle mass or people who are very sedentary. Treat it as a starting estimate and adjust based on your real-world results.

Can I increase my BMR?

Yes. Building muscle through strength training is the most effective long-term approach. Even a small increase in lean body mass can raise your resting calorie burn by 50 to 100 calories a day over time. Getting enough sleep also matters, as poor sleep has been linked to reduced metabolic function.

Does eating breakfast boost metabolism?

No. Skipping breakfast does not meaningfully slow your metabolic rate. BMR is driven by your body composition and size, not when you eat your first meal of the day. The idea that breakfast kicks your metabolism into gear each morning is a myth.

Should I eat my BMR calories if I am trying to lose weight?

Eating at or below your BMR for long periods is not recommended for most people. At very low intake, it becomes hard to get enough protein, vitamins and minerals, and muscle loss becomes more likely. A moderate deficit below your full TDEE is a healthier and more sustainable approach.

What is the difference between BMR and RMR?

BMR is measured under very strict conditions: a 12-hour fast, complete physical and mental rest. RMR (Resting Metabolic Rate) is measured under less strict conditions and tends to come out around 10 to 15% higher than BMR. Most online calculators technically estimate RMR but label the result as BMR.

How often should I recalculate?

Recalculate after a meaningful weight change (around 5 kg or more), after a sustained shift in your activity level, or roughly every 3 to 6 months. As your body weight and composition change, your BMR and TDEE change with it.