Learn the simple mathematical formulas for calculating percentage change, an essential skill for tracking prices, salaries, and metrics.
Understanding how to calculate percentage increase and decrease is an essential life skill. Whether you're figuring out how much your rent went up, calculating the return on an investment, or tracking weight loss, percentage change provides a clear, standardized way to measure growth or decline. You can perform these calculations instantly with our Percentage Calculator.
The Universal Formula
There is one master formula for calculating percentage change, whether it's an increase or a decrease:
If the result is a positive number, it is a percentage increase. If the result is a negative number, it is a percentage decrease.
Example 1: Calculating Percentage Increase
Let's say your monthly electricity bill was ₹1,200 last month (Old Value) and it is ₹1,500 this month (New Value). How much did it increase?
- Subtract the old value from the new value: 1,500 - 1,200 = 300. (This is the absolute increase).
- Divide the increase by the old value: 300 / 1,200 = 0.25.
- Multiply by 100 to get the percentage: 0.25 × 100 = 25%.
Your bill increased by 25%.
Example 2: Calculating Percentage Decrease
Imagine you bought a stock at ₹80 (Old Value) and its price dropped to ₹60 (New Value). What is the percentage decrease?
- Subtract the old value from the new value: 60 - 80 = -20.
- Divide by the old value: -20 / 80 = -0.25.
- Multiply by 100: -0.25 × 100 = -25%.
Your stock's value decreased by 25%.
A Common Trap: The Reversibility Myth
A very common mistake is assuming that percentage increases and decreases are perfectly reversible. They are not.
If a ₹100 item is marked up by 50%, the new price is ₹150. If that ₹150 item is then discounted by 50%, the final price is ₹75, NOT ₹100. Why? Because the 50% decrease is calculated on the new base of ₹150, not the original base of ₹100.
Always pay attention to what your base value (Old Value) is when calculating percentage changes.
Need a quick answer without doing the math? Use our Percentage Calculator to find percentage changes instantly.