A standard Body Mass Index (BMI) calculator helps you determine your current BMI based on your weight and height. A Reverse BMI Calculator works differently. Instead of inputting your current weight, you input a desired or target BMI value, along with your height, to calculate the ideal weight you should aim for to achieve that specific BMI. This tool is useful for individuals who have a specific weight goal in mind, whether it's to reach a healthy BMI range or a particular physique.
How is BMI Calculated?
The formula for BMI is:
BMI = (Weight in kilograms) / (Height in meters)^2
Or, if using pounds and inches:
BMI = (Weight in pounds / (Height in inches)^2) * 703
How the Reverse BMI Calculator Works
To find the target weight for a desired BMI, we rearrange the BMI formula. Using the metric system (kilograms and meters):
Weight (kg) = BMI * (Height in meters)^2
The calculator takes your target BMI and your height (converted to meters) to compute the corresponding weight in kilograms.
Understanding BMI Categories
Here are the general BMI categories as defined by the World Health Organization (WHO):
Underweight: Below 18.5
Normal weight: 18.5 – 24.9
Overweight: 25 – 29.9
Obesity: 30 or higher
Using the reverse BMI calculator can help you set realistic weight targets to fall within the "Normal weight" or a specific desired range.
When to Use a Reverse BMI Calculator
Setting Realistic Weight Goals: If you know your height and want to achieve a specific BMI (e.g., 22.5), this calculator tells you the target weight.
Fitness Planning: Athletes or fitness enthusiasts might use it to target a particular body composition.
Health Consultations: It can be a helpful tool when discussing weight goals with a healthcare provider or nutritionist.
Disclaimer: BMI is a screening tool and does not diagnose body fatness or health. Consult with a healthcare professional for personalized health advice.
function calculateWeight() {
var bmiValueInput = document.getElementById("bmiValue");
var heightCmInput = document.getElementById("heightCm");
var resultDiv = document.getElementById("result");
var bmiValue = parseFloat(bmiValueInput.value);
var heightCm = parseFloat(heightCmInput.value);
resultDiv.textContent = "; // Clear previous results
resultDiv.classList.remove('error');
// Input validation
if (isNaN(bmiValue) || isNaN(heightCm)) {
resultDiv.textContent = "Please enter valid numbers for BMI and Height.";
resultDiv.classList.add('error');
return;
}
if (bmiValue <= 0) {
resultDiv.textContent = "BMI value must be positive.";
resultDiv.classList.add('error');
return;
}
if (heightCm <= 0) {
resultDiv.textContent = "Height must be a positive value.";
resultDiv.classList.add('error');
return;
}
// Convert height from cm to meters
var heightM = heightCm / 100;
// Calculate target weight in kg
// Formula: Weight (kg) = BMI * (Height in meters)^2
var targetWeightKg = bmiValue * (heightM * heightM);
// Display the result
// Using toFixed(2) for two decimal places for weight
resultDiv.textContent = "Target Weight: " + targetWeightKg.toFixed(2) + " kg";
}