Understanding BMR and TDEE Properly to Find Your Right Daily Calories

When you start a diet, the very first question you run into is, "How many calories should I eat in a day?" Every YouTube channel and every app gives a different number, so it's no wonder it gets confusing. The truth is, the right answer isn't decided by someone else, it comes from the energy your own body uses each day. The two key concepts behind this are your Basal Metabolic Rate (BMR) and your Total Daily Energy Expenditure (TDEE). Today, let's actually calculate both of these and work through how to set your own appropriate calorie target.

What is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate (BMR) is the energy your body burns just lying down and breathing all day. These are the calories spent keeping you alive, things like your heartbeat, breathing, maintaining body temperature, and organ function. Remarkably, about 60–70% of your total daily calorie burn goes here. In other words, even without exercising, your body is already using quite a lot of energy by default. The reason a higher muscle mass raises your BMR is that muscle is tissue that burns energy even when you're at rest.

Calculating Your BMR (the Mifflin-St Jeor formula)

The most widely used and most accurate formula is the Mifflin-St Jeor equation. You just plug in your weight (kg), height (cm), and age (years).

• Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
• Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
• Ex.) A 30-year-old woman, 162cm tall, 60kg → (10×60) + (6.25×162) − (5×30) − 161 = 600 + 1012.5 − 150 − 161 ≈ 1,302kcal
• Ex.) A 35-year-old man, 175cm tall, 75kg → (10×75) + (6.25×175) − (5×35) + 5 = 750 + 1093.75 − 175 + 5 ≈ 1,674kcal

TDEE: The Total Calories You Actually Burn in a Day

BMR is the number for when you're 'only lying down.' But we go to work, walk around, and exercise too. The value you get by multiplying in your activity level is your TDEE (Total Daily Energy Expenditure), the total calories you actually burn in a day. Your diet calorie target should be based on this TDEE, not on your BMR. You calculate it by multiplying your BMR by an activity factor.

• Barely moves (sedentary lifestyle): BMR × 1.2
• Light activity (exercise 1–3 times/week): BMR × 1.375
• Moderate activity (exercise 3–5 times/week): BMR × 1.55
• Active (exercise 6–7 times/week): BMR × 1.725
• Ex.) The woman above (BMR 1,302) × 1.375 = about 1,790kcal as her maintenance calories

Setting Your Right Weight-Loss Calorie Target

To lose 1kg of body fat, you need a calorie deficit (intake < expenditure) of about 7,700kcal. So the key is to 'eat less than your TDEE,' not to starve yourself outright. A gentle deficit of about 300–500kcal per day off your TDEE is generally recommended. For the woman above (TDEE about 1,790kcal), that means setting a target of roughly 1,300–1,500kcal per day. Done this way, in theory you can lose weight at a healthy pace of about 0.3–0.5kg per week, or about 1.5–2kg per month.

How to Distribute Nutrients Within Your Calorie Deficit

Even at the same calorie count, what you fill it with matters. During a weight-loss phase in particular, eating enough protein is key to preventing muscle loss. Generally, about 1.2–1.6g of protein per kg of body weight is recommended during weight loss (e.g., about 72–96g for someone weighing 60kg). Rather than slashing carbs and fats to the extreme, distribute them in a balanced way, and boosting fullness with fiber-rich vegetables and whole grains lets you get by feeling less hungry even on fewer calories.

1. ① Calculate your BMR using the Mifflin-St Jeor formula
2. ② Multiply by an activity factor to get your TDEE (maintenance calories)
3. ③ Subtract 300–500kcal from your TDEE to set your target calories
4. ④ Secure protein first at 1.2–1.6g per kg of body weight
5. ⑤ Fill the remaining calories with carbs and fats, and add fullness with vegetables
6. ⑥ Watch your weight change over 2–4 weeks and fine-tune your calories

The Trap of Rapid Weight Loss: Rebound and Muscle Loss

Extreme calorie restriction like 800kcal a day makes your weight drop fast at first, but a large part of what you lose is water and muscle. When muscle decreases, your BMR drops along with it, which easily leads to a 'plateau' where you stop losing weight even while eating little, and to the dreaded 'rebound.' Also, if you cut your sleep short or are under heavy stress, the appetite hormone ghrelin rises while the satiety hormone leptin falls, so the urge to binge grows regardless of your willpower. That's why getting enough sleep (around 7 hours) is also part of dieting.

The starting point of a diet isn't 'how little you eat,' but knowing 'how much you burn in a day.'

To sum up, the most sustainable diet formula is to know your basic burn through your BMR, multiply by your activity level to find your TDEE, and then create a gentle deficit from there. The people who get enough protein, sleep well, and lose weight slowly are the ones who make it to the end. That said, the calculations and guidance in this article are general references, not medical advice. If you have an underlying condition such as diabetes or thyroid disease, or are pregnant or breastfeeding, please be sure to consult a doctor or nutrition professional before restricting calories.