The Body Mass Index (BMI) is a widely used metric to categorize a person's weight relative to their height. While commonly used to assess if someone is underweight, normal weight, overweight, or obese based on their current weight, a BMI Reverse Calculator helps answer a different question: "Given a desired BMI and my current height, what weight should I be?" This tool is invaluable for individuals setting health and fitness goals, such as aiming for a specific weight range or understanding what weight corresponds to a healthy BMI category for their stature.
The BMI Formula
The standard formula for calculating BMI is:
BMI = weight (kg) / height (m)²
Where:
weight is measured in kilograms (kg).
height is measured in meters (m).
How the BMI Reverse Calculator Works
The reverse BMI calculator rearranges the standard BMI formula to solve for weight. To do this, we first isolate the weight component:
Starting with: BMI = weight / height²
Multiply both sides by height²:
weight = BMI * height²
This is the core calculation performed by this reverse calculator. You input your desired BMI value and your current height in meters, and the calculator outputs the target weight in kilograms that would achieve that BMI.
Use Cases for a BMI Reverse Calculator
Setting Realistic Weight Goals: If you know a healthy BMI range is, for instance, 18.5 to 24.9, you can use the calculator to determine the specific weight targets within that range for your height.
Fitness Planning: Personal trainers or individuals can use this to set appropriate weight benchmarks for training programs.
Understanding Health Categories: If someone wants to know what weight they need to be to fall out of the "overweight" category (BMI > 25) or into the "normal" range (BMI 18.5-24.9), this calculator provides the exact number.
General Health Awareness: It provides a clear numerical target for weight management efforts, making goals more tangible.
Example Calculation
Let's say you want to achieve a BMI of 22.5 (which is well within the healthy range) and your current height is 1.70 meters.
Using the reverse formula:
Target Weight = Target BMI * (Height in meters)²
Target Weight = 22.5 * (1.70)²
Target Weight = 22.5 * 2.89
Target Weight = 65.025 kg
Therefore, to achieve a BMI of 22.5 with a height of 1.70 meters, your target weight would be approximately 65.03 kg.
The BMI Reverse Calculator is a straightforward yet powerful tool for anyone looking to quantify their weight management goals based on the universally recognized BMI scale.
function calculateReverseBmi() {
var targetBmiInput = document.getElementById("targetBmi");
var currentHeightInput = document.getElementById("currentHeight");
var resultDiv = document.getElementById("result");
var targetBmi = parseFloat(targetBmiInput.value);
var currentHeight = parseFloat(currentHeightInput.value);
// Clear previous result
resultDiv.innerHTML = "";
resultDiv.style.display = "none";
resultDiv.style.backgroundColor = "var(–success-green)"; // Reset color
// Input validation
if (isNaN(targetBmi) || targetBmi <= 0) {
resultDiv.innerHTML = "Please enter a valid target BMI.";
resultDiv.style.backgroundColor = "#dc3545"; // Error color
resultDiv.style.display = "block";
return;
}
if (isNaN(currentHeight) || currentHeight <= 0) {
resultDiv.innerHTML = "Please enter a valid height in meters (e.g., 1.75).";
resultDiv.style.backgroundColor = "#dc3545"; // Error color
resultDiv.style.display = "block";
return;
}
// Calculation: weight = BMI * height^2
var targetWeight = targetBmi * Math.pow(currentHeight, 2);
// Display result with formatting
resultDiv.innerHTML = targetWeight.toFixed(2) + " kg" +
"Your target weight for a BMI of " + targetBmi + " at " + currentHeight + " meters height.";
resultDiv.style.display = "block";
}