Sedentary (Little or no exercise)
Lightly Active (Exercise 1-3 days/week)
Moderately Active (Exercise 3-5 days/week)
Very Active (Exercise 6-7 days/week)
Extra Active (Physical job or training 2x/day)
Please enter valid values for Age, Height, and Weight.
Basal Metabolic Rate (BMR)
0kcal/day
Calories burned at complete rest
Total Daily Energy Expenditure (TDEE)
0kcal/day
Calories needed to maintain current weight
Calorie Needs by Goal
Mild Weight Loss (-0.25kg/week)0 kcal
Weight Loss (-0.5kg/week)0 kcal
Extreme Weight Loss (-1kg/week)0 kcal
Mild Weight Gain (+0.25kg/week)0 kcal
Understanding Your Metabolic Rate in the UK
Whether you are trying to lose weight, gain muscle, or simply maintain a healthy lifestyle, understanding your numbers is the first step. This Metabolic Rate Calculator UK is designed specifically for British users, allowing you to input your weight in Stone and Pounds and your height in Feet and Inches, converting them seamlessly into the scientific metrics required for accurate calculation.
What is BMR (Basal Metabolic Rate)?
Your Basal Metabolic Rate (BMR) represents the number of calories your body burns while at complete rest. Imagine you stayed in bed all day without moving; your body would still consume energy to keep your heart beating, lungs breathing, and brain functioning. For most people, BMR accounts for about 60-75% of total daily calorie expenditure.
Knowing your BMR is crucial because it acts as the baseline for all dietary planning. Eating significantly below your BMR can be dangerous and may actually slow down your metabolism.
What is TDEE (Total Daily Energy Expenditure)?
While BMR is what you burn at rest, your TDEE includes the energy you burn through physical activity and the digestion of food. This calculator uses the standard multipliers to adjust your BMR based on your lifestyle:
Sedentary: Desk job, little to no exercise.
Lightly Active: Walking or light exercise 1-3 times a week.
Moderately Active: Moderate exercise or sports 3-5 days a week.
Very Active: Hard exercise or physical job 6-7 days a week.
The Formula Used
This calculator utilises the Mifflin-St Jeor equation, widely considered by the NHS and dietetic associations to be the most accurate formula for estimating calorie needs in healthy adults. The formula calculates metric BMR as follows:
Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Our tool automatically converts your input of Stones/Pounds to Kilograms and Feet/Inches to Centimetres before running this calculation.
How to Use These Results
Once you have your TDEE (Maintenance Calories), you can adjust your intake based on your goals:
To Lose Weight: Aim for a deficit of 500 calories per day to lose approximately 1lb (0.45kg) per week.
To Gain Muscle: Aim for a surplus of 250-500 calories per day, combined with resistance training.
To Maintain: Simply eat roughly the amount of calories shown in your TDEE result.
Note: Metabolism varies from person to person. Use these numbers as a starting point and adjust based on your progress over 2-3 weeks.
function calculateMetabolism() {
// 1. Get Inputs
var gender = document.getElementById('gender').value;
var age = parseFloat(document.getElementById('age').value);
var feet = parseFloat(document.getElementById('heightFt').value);
var inches = parseFloat(document.getElementById('heightIn').value);
var stones = parseFloat(document.getElementById('weightSt').value);
var pounds = parseFloat(document.getElementById('weightLbs').value);
var activityLevel = parseFloat(document.getElementById('activity').value);
// 2. Input Validation (Handling NaNs and empty fields)
if (isNaN(age) || isNaN(feet) || isNaN(stones)) {
document.getElementById('error-message').style.display = 'block';
document.getElementById('results-area').style.display = 'none';
return;
}
// Handle inches or pounds being empty (treat as 0)
if (isNaN(inches)) inches = 0;
if (isNaN(pounds)) pounds = 0;
document.getElementById('error-message').style.display = 'none';
// 3. Convert Imperial to Metric for Formula
// 1 Foot = 30.48 cm, 1 Inch = 2.54 cm
var heightCm = (feet * 30.48) + (inches * 2.54);
// 1 Stone = 6.35029 kg, 1 Pound = 0.453592 kg
var weightKg = (stones * 6.35029) + (pounds * 0.453592);
// 4. Calculate BMR (Mifflin-St Jeor Equation)
var bmr = 0;
if (gender === 'male') {
// Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else {
// Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
// 5. Calculate TDEE
var tdee = bmr * activityLevel;
// 6. Calculate Goals (Deficits and Surpluses)
// 1lb fat approx 3500 calories. 500 cal deficit/day = 1lb loss/week
var mildLoss = tdee – 250;
var standardLoss = tdee – 500;
var extremeLoss = tdee – 1000;
var mildGain = tdee + 250;
// Safety check for extreme loss (don't go below BMR ideally, or 1200)
if (extremeLoss < 1200) {
// Just a visual flag logic or keep raw numbers, usually keep raw but maybe warn in real app
// We will output raw math for calculator purity
}
// 7. Update UI
document.getElementById('bmr-result').innerText = Math.round(bmr);
document.getElementById('tdee-result').innerText = Math.round(tdee);
document.getElementById('loss-mild').innerText = Math.round(mildLoss) + " kcal";
document.getElementById('loss-standard').innerText = Math.round(standardLoss) + " kcal";
document.getElementById('loss-extreme').innerText = Math.round(extremeLoss) + " kcal";
document.getElementById('gain-mild').innerText = Math.round(mildGain) + " kcal";
document.getElementById('results-area').style.display = 'block';
}