When you start a diet or a fitness plan, the first stumbling block is usually the question “how many calories should I actually eat?” Search online and you get different numbers from different people, and the difference between “basal metabolic rate” and “calories burned” is easy to mix up.
In this guide, we explain how to calculate your basal metabolic rate (BMR) and daily calorie needs in plain terms. You will learn the widely used Mifflin-St Jeor equation, how to choose an activity level, and how to set intake targets for losing, maintaining or gaining weight.
BMR vs total daily energy expenditure
Let’s start by untangling two terms that are often confused:
| Term | Meaning | Includes |
|---|---|---|
| BMR (basal metabolic rate) | Energy burned at complete rest | Heartbeat, breathing, body temperature |
| TDEE (total daily energy expenditure) | BMR plus all activity | Walking, work, exercise, chores |
Your BMR is the minimum energy needed to stay alive, and it typically accounts for 60-70% of your total daily burn. The remaining 30-40% comes from activity. For weight management, what matters is the gap between the calories you eat and your TDEE.
Units: calories are measured in kilocalories (kcal) - the unit printed on food labels. This guide uses kcal throughout.
Calculating BMR with the Mifflin-St Jeor equation
Several formulas exist for estimating BMR, but the one most commonly recommended today is the Mifflin-St Jeor equation. It uses sex, age, height and weight:
Men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161Worked example
For a 30-year-old man who is 170 cm tall and weighs 65 kg:
10 × 65 + 6.25 × 170 − 5 × 30 + 5
= 650 + 1062.5 − 150 + 5
= 1567.5 → about 1,568 kcalFor a 25-year-old woman at 160 cm and 50 kg:
10 × 50 + 6.25 × 160 − 5 × 25 − 161
= 500 + 1000 − 125 − 161
= 1214 kcalWhy it drops with age: muscle mass tends to decline as we age, which lowers BMR. At the same weight, someone with more muscle burns more at rest - so regular exercise has a lasting effect on your daily burn.
Multiply by activity level for total daily burn
Multiplying BMR by an activity factor gives your total daily energy expenditure (TDEE). Five levels are commonly used:
| Activity level | Factor | Typical lifestyle |
|---|---|---|
| Mostly inactive | ×1.2 | Desk job, little exercise |
| Light (1-3 days/week) | ×1.375 | Occasional walks or light workouts |
| Moderate (3-5 days/week) | ×1.55 | Regular gym or sports |
| Active (6-7 days/week) | ×1.725 | Exercise almost every day |
| Very active | ×1.9 | Athlete-level training |
Using our example (30-year-old man, BMR of 1,568 kcal) with light activity (×1.375):
1568 × 1.375 = about 2,155 kcalThat is his total daily energy expenditure - roughly the amount he can eat to maintain his current weight.
Setting intake targets
Once you know your TDEE, adjust intake based on your goal:
| Goal | Suggested intake |
|---|---|
| Losing weight | TDEE − 500 kcal |
| Maintaining | Around TDEE |
| Gaining weight | TDEE + 500 kcal |
For our example, that is about 1,655 kcal to lose and 2,655 kcal to gain. A 500 kcal adjustment corresponds to roughly 2 kg of change per month and is widely used as a moderate pace.
Caution: cutting calories too aggressively causes muscle loss, lowers your BMR and makes regain more likely. Keep intake above about 1,200 kcal and aim for 0.5-1 kg per week at most. If you have health conditions or plan a large change, consult a doctor or registered dietitian.
How to use the Tools Hub calorie calculator
Doing this by hand invites arithmetic errors. The Tools Hub calorie & BMR calculator takes your sex, age, height, weight and activity level, then shows your BMR, TDEE and target intakes at once. Your details never leave your browser.
How to use it (three steps)
Enter your details
Select your sex and enter your age, height and weight.
Pick an activity level
Choose one of five levels matching how often you exercise. When unsure, choose the lower level.
Check the results
Your BMR, TDEE and target intakes for losing, maintaining and gaining appear instantly.
The tool from this guide
Calorie & BMR Calculator
Free, no sign-up required, and everything runs in your browser.
Summary
- BMR is the energy burned at rest; TDEE adds all daily activity on top of it
- Estimate BMR with the Mifflin-St Jeor equation using sex, age, height and weight
- TDEE = BMR × activity factor (five levels from 1.2 to 1.9)
- Losing weight means eating about TDEE − 500 kcal; gaining means TDEE + 500 kcal
- Extreme restriction backfires; keep intake above about 1,200 kcal
- Results are estimates - adjust based on your actual weight trend
Calorie calculation is the first step toward understanding how much energy your body actually uses each day. Knowing the number lets you adjust food and exercise gradually - which is what makes a diet sustainable.
FAQ
What is basal metabolic rate?
It is the energy your body burns at rest - the minimum required for your heartbeat, breathing and body temperature. In adults it typically makes up 60-70% of total daily burn.
How do I calculate my daily calorie needs?
Calculate BMR with the Mifflin-St Jeor equation, then multiply by an activity factor between 1.2 and 1.9. If doing this by hand feels tedious, the Tools Hub calculator computes it automatically.
How do I set a calorie target for weight loss?
Subtract 500 kcal from your total daily burn - roughly a 2 kg loss per month. Keep intake above 1,200 kcal and avoid extreme restrictions.
How accurate is the result?
These are estimates. Actual burn varies with muscle mass, individual differences and day-to-day activity. Track your weight over several weeks and fine-tune your intake accordingly.
