function calculatePercentageIncrease() {
// Get input values using standard JS
var oldRateInput = document.getElementById('oldRate');
var newRateInput = document.getElementById('newRate');
var resultBox = document.getElementById('resultBox');
var errorMsg = document.getElementById('errorMsg');
var diffDisplay = document.getElementById('diffDisplay');
var percentDisplay = document.getElementById('percentDisplay');
// Parse values
var oldRate = parseFloat(oldRateInput.value);
var newRate = parseFloat(newRateInput.value);
// Validation logic
if (isNaN(oldRate) || isNaN(newRate)) {
errorMsg.style.display = 'block';
resultBox.style.display = 'none';
errorMsg.innerText = "Please enter valid numbers for both fields.";
return;
}
// Check for division by zero
if (oldRate === 0) {
errorMsg.style.display = 'block';
resultBox.style.display = 'none';
errorMsg.innerText = "The original rate cannot be zero when calculating percentage increase.";
return;
}
errorMsg.style.display = 'none';
// Calculation Logic
var difference = newRate – oldRate;
var percentage = (difference / oldRate) * 100;
// Formatting results
// If the result is negative, it indicates a decrease
var sign = difference > 0 ? "+" : "";
diffDisplay.innerText = sign + difference.toFixed(2);
percentDisplay.innerText = sign + percentage.toFixed(2) + "%";
// Display results
resultBox.style.display = 'block';
}
How to Calculate Percentage of Rate Increase
Understanding how to calculate the percentage of a rate increase is a fundamental mathematical skill used in various real-world scenarios, from analyzing pay raises and inflation adjustments to tracking utility bill hikes or subscription fee changes. It allows you to standardize the change between two numbers to understand the relative magnitude of the increase.
The Rate Increase Formula
To calculate the percentage increase between an original rate and a new rate, use the following formula:
Percentage Increase = ((New Rate – Original Rate) / Original Rate) × 100
This formula determines the difference between the two values, divides that difference by the starting value (the baseline), and then multiplies by 100 to convert the decimal into a percentage.
Step-by-Step Calculation Guide
Identify the Original Rate: This is your starting number or baseline value before the increase occurred.
Identify the New Rate: This is the current number or the value after the increase.
Calculate the Difference: Subtract the Original Rate from the New Rate (New – Original).
Divide by the Original: Take the result from step 3 and divide it by the Original Rate.
Convert to Percentage: Multiply the result by 100 to get the percentage.
Real-World Examples
Example 1: Hourly Wage Increase
Imagine your hourly wage was $25.00 (Original Rate) and it was increased to $28.50 (New Rate). How much did your pay rate increase in percentage terms?
Difference: 28.50 – 25.00 = 3.50
Division: 3.50 / 25.00 = 0.14
Percentage: 0.14 × 100 = 14%
Your hourly rate increased by 14%.
Example 2: Subscription Price Hike
A streaming service raises its monthly fee from $12 to $15.
Difference: 15 – 12 = 3
Division: 3 / 12 = 0.25
Percentage: 0.25 × 100 = 25%
The subscription rate increased by 25%.
Why is the "Original Rate" important?
The most common mistake when calculating percentage increase is dividing by the New Rate instead of the Original Rate. Percentages are always relative to the starting point. If you divide by the new rate, you are calculating what portion of the current cost is made up of the increase, which is a different metric entirely.
Handling Negative Results
If your calculation results in a negative number (e.g., -10%), this indicates a rate decrease rather than an increase. The formula works for both scenarios. If the new rate is lower than the old rate, the percentage change will be negative, signifying a reduction in value.