BMR & TDEE Calculator

Your body is a furnace that never shuts off. Even if you spent an entire day motionless in bed, your heart would beat roughly 100,000 times, your lungs would cycle through 20,000 breaths, and your brain would consume about 20% of your energy just to keep the lights on. This baseline energy cost is your Basal Metabolic Rate, or BMR. It represents the absolute minimum calories your body needs to keep you alive.

But you don't spend your days motionless. You walk to the kitchen, climb stairs, fidget during meetings, and maybe hit the gym. Total Daily Energy Expenditure (TDEE) accounts for all of this activity by multiplying your BMR by an activity factor. A sedentary office worker might multiply their BMR by 1.2, while a construction worker who also trains might use 1.9. The result is your actual daily calorie burn, and it's the number that actually matters for weight management.

This calculator gives you both numbers using three different scientific formulas, then shows exactly how many calories to eat whether you want to lose fat, maintain your current weight, or build muscle. No guesswork, just math.

The Mifflin-St Jeor equation, developed in 1990, has become the gold standard because it predicts BMR within 10% accuracy for most people. For men, the formula is: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women, replace the +5 with −161. Take a 35-year-old man who weighs 82 kg and stands 178 cm tall. His calculation runs: (10 × 82) + (6.25 × 178) − (5 × 35) + 5, which equals 820 + 1112.5 − 175 + 5, giving a BMR of 1,762 calories.

To find his TDEE, multiply this BMR by an activity multiplier. If he exercises moderately three times per week and has a desk job, the standard multiplier is 1.55. So 1,762 × 1.55 equals 2,731 calories per day. This is his maintenance level. Eating 500 fewer calories daily (about 2,230) would create a weekly deficit of 3,500 calories, roughly one pound of fat loss.

The calculator also shows Harris-Benedict and Katch-McArdle results for comparison. Harris-Benedict tends to run slightly higher, sometimes by 50-100 calories. Katch-McArdle requires your body fat percentage but rewards you with better accuracy if you have that measurement.

Sarah is a 42-year-old nurse who weighs 74 kg, stands 165 cm, and wants to lose about 5 kg before her daughter's wedding in three months. She enters her stats into the calculator and selects 'lightly active' since she's on her feet all day but doesn't formally exercise. Her BMR comes out to 1,418 calories, and her TDEE lands at 1,950 calories.

For sustainable fat loss, the calculator suggests a moderate deficit of 400-500 calories below maintenance. Sarah chooses 1,500 calories daily, creating a 450-calorie daily deficit. Over 12 weeks, this deficit totals about 37,800 calories, equivalent to roughly 4.8 kg of fat. She's right on target without resorting to extreme restriction.

The macro breakdown helps her structure meals. At 1,500 calories with a moderate protein target of 1.6 grams per kilogram of body weight, she needs about 118 grams of protein daily. The calculator suggests filling remaining calories with roughly 45% carbohydrates and 25% fats, giving her enough energy for her demanding shifts while preserving muscle mass.

Competitive athletes use these calculations for reverse dieting after a strict cut. A bodybuilder who competed at 1,800 calories doesn't jump straight back to their TDEE of 2,600. Instead, they add 100-150 calories weekly, letting their metabolism recover gradually while minimizing fat regain. The calculator's maintenance number becomes a destination, not a starting point.

People recovering from eating disorders also find these numbers helpful as objective anchors. When your relationship with food has been chaotic, having a scientifically calculated maintenance target removes some of the anxiety around eating enough. A therapist might use the TDEE figure to show a client that eating 2,200 calories isn't excessive for their body, it's actually what keeps them healthy.

Shift workers face a particular challenge since their activity levels vary wildly. A nurse working three 12-hour shifts might use the 'very active' multiplier on work days and 'sedentary' on days off, then average the two TDEE values for weekly meal planning.

The most common error is overestimating activity level. That gym session three times a week doesn't make you 'very active' if you sit at a desk the other 160 waking hours. Most people with office jobs who exercise regularly are genuinely 'lightly active' at best. Choosing 'moderately active' when you shouldn't can inflate your TDEE by 300 or more calories, erasing your entire planned deficit.

Another frequent mistake is treating these numbers as gospel rather than starting points. Your actual metabolic rate might be 10-15% higher or lower than any formula predicts due to genetics, hormonal status, or metabolic adaptation. Use the calculator's output for two weeks, track your weight, and adjust if nothing changes. If you're eating at the suggested deficit but the scale hasn't moved, cut another 100-150 calories.

Ignoring the formula differences also causes problems. Someone with 30% body fat will get more accurate results from Mifflin-St Jeor, while a lean athlete with 12% body fat should trust Katch-McArdle instead. Running all three formulas and comparing the outputs helps you spot which one aligns best with your real-world experience.