Whether you want to lose weight, gain muscle, or maintain your current physique, everything starts with one number: your daily calorie needs. Eat too little and your body slows down. Eat too much and you gain weight. Finding the right balance is the key to reaching your goals.
What Is BMR?
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep you alive. It powers your breathing, circulation, cell production, brain function, and all the things your body does without you thinking about it.
BMR typically accounts for 60-70% of your total daily calorie burn. That means most of the calories you consume are used just to stay alive, not for walking, exercise, or digestion.
The Mifflin-St Jeor Equation
There are several formulas to estimate BMR, but the Mifflin-St Jeor equation is considered the most accurate for most people. It's used by the Academy of Nutrition and Dietetics and is the clinical gold standard (Mifflin MD, et al., American Journal of Clinical Nutrition, 1990).
Example: A 30-year-old male, 175 cm, 70 kg:
BMR = (10 × 70) + (6.25 × 175) - (5 × 30) - 5 = 700 + 1093.75 - 150 - 5 = 1,639 kcal/day
From BMR to TDEE
Your BMR is just the resting burn. To find your total daily energy expenditure (TDEE), you multiply BMR by an activity factor:
- Sedentary (desk job, little exercise): BMR × 1.2
- Lightly active (exercise 1-2 days/week): BMR × 1.375
- Moderately active (exercise 3-5 days/week): BMR × 1.55
- Very active (exercise 6-7 days/week): BMR × 1.725
- Super active (athlete, daily intense): BMR × 1.9
Using our example (BMR = 1,639, moderately active):
TDEE = 1,639 × 1.55 = 2,540 kcal/day — this is the amount to maintain current weight.
Why Your Number Changes (and How to Recalibrate It)
The activity multipliers above are population averages, not laws. Real-world needs vary with body composition, daily movement (NEAT), and hormones. You can recalibrate your estimate with a simple home experiment over 3-4 weeks: track your weight and food intake carefully, then compare actual progress to expected. As a rough anchor, a sustained deficit of about 3,500 kcal produces roughly one pound (0.45 kg) of weight change — so if you are losing about a pound a week while eating 2,000 kcal, your real maintenance is closer to 2,500. Re-run the calorie calculator whenever your weight shifts by 5-10 pounds; the number that worked at your starting weight will quietly stop being right.
Setting Your Calorie Target
To Lose Weight
Creating a calorie deficit of 500 kcal/day results in approximately 0.5 kg (1 lb) of fat loss per week. This is considered a safe and sustainable rate. Going below 1,200 kcal/day for women or 1,500 kcal/day for men is generally not recommended without medical supervision.
To Gain Weight
A surplus of 300-500 kcal/day combined with strength training promotes lean muscle gain. Gaining more than 0.25-0.5 kg per week usually means you're also gaining excess fat.
To Maintain
Eating at your TDEE maintains your current weight. This is the goal for people who are happy with their body composition and want to sustain their lifestyle.
Find your exact calorie needs in seconds
Use the Calorie Calculator →Common Mistakes
- Ignoring exercise calories — activity multipliers already account for your exercise level; don't double-count
- Eating too little — severe restriction slows metabolism and causes muscle loss
- Not tracking accurately — portion sizes are often underestimated by 30-50%
- Using BMI as calorie guide — BMI doesn't tell you your calorie needs; BMR does
- Expecting linear progress — weight loss has plateaus; consistency matters more than perfection
The Bottom Line
Calculate your BMR using the Mifflin-St Jeor equation, multiply by your activity level to get TDEE, then adjust by 300-500 kcal based on your goal. Track for 2-3 weeks and adjust as needed. Your metabolism isn't static — it adapts. The most important thing is consistency over time, not perfection on any single day.