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Accurate BMR Calculator

Male Female

Your Basal Metabolic Rate (BMR)

Calories per day at rest

function calculateBMR() { var gender = document.getElementById("gender").value; var weight = parseFloat(document.getElementById("weight").value); var height = parseFloat(document.getElementById("height").value); var age = parseInt(document.getElementById("age").value); var resultBox = document.getElementById("bmr-result-box"); var output = document.getElementById("bmr-output"); if (isNaN(weight) || isNaN(height) || isNaN(age) || weight <= 0 || height <= 0 || age <= 0) { alert("Please enter valid positive numbers for weight, height, and age."); return; } var bmr = 0; // Mifflin-St Jeor Equation if (gender === "male") { bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5; } else { bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161; } output.innerHTML = Math.round(bmr).toLocaleString() + " kcal"; resultBox.style.display = "block"; }

Understanding Your Basal Metabolic Rate (BMR)

Your Basal Metabolic Rate, or BMR, is the minimum number of calories your body needs to function while at rest. Even when you are sleeping or sitting perfectly still, your body is hard at work circulating blood, breathing, regulating body temperature, and growing new cells. BMR accounts for roughly 60% to 75% of the total calories you burn each day.

The Science: The Mifflin-St Jeor Equation

This calculator utilizes the Mifflin-St Jeor Equation, which is currently considered the most accurate formula for predicting BMR in healthy adults. Developed in 1990, it replaced the older Harris-Benedict formula because it more accurately reflects modern lifestyles and body compositions.

  • Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
  • Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

BMR vs. TDEE: What's the Difference?

It is important to remember that your BMR is not your total daily calorie requirement. To find your Total Daily Energy Expenditure (TDEE), you must multiply your BMR by an activity factor:

Activity Level Multiplier
Sedentary (Little or no exercise) BMR x 1.2
Lightly Active (1-3 days/week) BMR x 1.375
Moderately Active (3-5 days/week) BMR x 1.55
Very Active (6-7 days/week) BMR x 1.725

Realistic Example Calculation

Let's look at a 35-year-old male who weighs 85kg and stands 180cm tall:

  1. (10 × 85) = 850
  2. (6.25 × 180) = 1,125
  3. (5 × 35) = 175
  4. Calculation: 850 + 1,125 – 175 + 5 = 1,805 Calories

In this scenario, the individual requires 1,805 calories just to maintain vital organ function. If he has a desk job and does no exercise, his actual daily maintenance calories would be approximately 2,166 (1,805 x 1.2).

Why Should You Know Your BMR?

Whether your goal is weight loss, muscle gain, or weight maintenance, BMR is your starting line. To lose weight, you typically need to consume fewer calories than your TDEE (creating a calorie deficit). Knowing your BMR ensures you don't drop your calorie intake dangerously low, which can stall your metabolism and cause muscle loss.

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