Calorie Calculator

How do BMR and TDEE actually work?

Calculating your calorie needs might seem like a science project, but it comes down to a few basic variables: how much energy your body needs to survive at rest, and how much extra energy you expend going about your day. Your Basal Metabolic Rate (BMR) represents that baseline survival energy. If you stayed in bed all day without moving a single finger, your heart, lungs, and brain would still burn your BMR calories just to keep you alive.

Once you add in physical movements — from typing at your desk and brushing your teeth to intense lifting sessions or running marathons — you get your Total Daily Energy Expenditure (TDEE). Think of TDEE as your caloric "break-even" point. If you consume exactly your TDEE in food every day, your weight will remain practically unchanged.

The Mifflin-St Jeor Formula: Why We Use It

There are several popular formulas for calculating metabolic rates, including the classic Harris-Benedict equation. However, modern nutritional science and clinical studies generally favor the Mifflin-St Jeor equation because it has proven to be the most accurate predictor of metabolic rate for the vast majority of healthy adults. Developed in the 1990s, it provides a tighter calculation that aligns closer to actual measured laboratory results than older mathematical models.

While no formula is 100% perfect (since it cannot account for differences in lean muscle mass or genetics without advanced tools), Mifflin-St Jeor provides a highly reliable starting line. If you find you are losing or gaining weight slower than calculated, you can easily adjust your daily intake by 100–200 calories to match your real-world progress.

Navigating Deficits, Surpluses, and Macro Splits

To lose weight, you must create a calorie deficit; to gain weight, a calorie surplus. We've structured the goals here based on the standard guideline that 1 kg of body fat is roughly equivalent to 7,700 calories of stored energy. This means that reducing your intake by 550 calories below your TDEE each day will result in approximately 0.5 kg of weight loss per week. However, we strongly suggest not letting your daily calories dip below 1,200 for women or 1,500 for men unless guided by a professional. Doing so makes it incredibly hard to hit your essential micronutrient goals.

Once your target calorie number is set, how you divide those calories between carbohydrates, proteins, and fats (your macro split) defines how you feel and perform. A balanced approach works beautifully for general activity. If you are highly active and focused on muscle retention or muscle growth, raising protein ratios to 30%–40% supports muscle protein synthesis. Meanwhile, people looking to keep insulin levels low or manage hunger triggers often find success with a lower-carb profile.