๐Percentage Change Calculator
Find percentage increase, decrease, or reverse a known percentage change to find the original value.
Free Percentage Change Calculator
Our free percentage change calculator finds the percentage increase or decrease between two numbers instantly. Enter an original value and a new value, and get the exact percentage change along with the absolute difference โ perfect for tracking price changes, salary raises, weight loss, or any before-and-after comparison.
Switch to reverse mode to solve the opposite problem: if you know a value increased or decreased by a certain percentage, this tool works backward to find the original starting value. This is useful for figuring out a pre-discount price or a pre-raise salary.
Every result shows the formula and substitution used, so you can follow the math rather than just trust a black-box answer. No sign-up, no downloads โ everything runs instantly in your browser.
About the Percentage Change Calculator
Features
Two modes
Calculate % change between two values, or reverse a known % change to find the original.
Handles negatives
Correctly computes percentage change even when values cross or start below zero.
Step-by-step working
See the exact formula and substitution used to reach the result.
Instant validation
Undefined cases, like a zero original value, are flagged clearly.
Frequently Asked Questions
How is percentage change calculated?
Percentage change is calculated as (New Value โ Original Value) divided by the absolute value of the Original Value, multiplied by 100.
What's the difference between percentage increase and decrease?
A percentage increase is a positive percentage change (the new value is larger), while a percentage decrease is a negative percentage change (the new value is smaller).
What does reverse percentage mean?
Reverse percentage means working backward from a known result and percentage change to find the original starting value, such as finding a pre-discount price from a sale price and discount percentage.
Why can't the original value be zero?
Percentage change divides by the original value, so if it's zero the calculation is undefined (division by zero).
Can percentage change be negative?
Yes. A negative percentage change means the new value is smaller than the original, indicating a decrease.
How do I find the original price before a discount?
Use reverse mode: enter the sale price as the resulting value and the discount as a negative percentage (e.g. -20 for a 20% discount) to recover the original price.
Can I use this for salary raises?
Yes. Enter your old salary as the original value and your new salary as the new value to see the percentage raise.
What happens with a -100% change in reverse mode?
A -100% change means the value went to zero, so the original value cannot be mathematically recovered from a zero result; the calculator flags this case.
Does this handle negative values?
Yes, the formula uses the absolute value of the original number, so it correctly handles cases where values cross zero or start negative.
Is this calculator free to use?
Yes, the percentage change calculator is completely free with no sign-up, and all calculations run instantly in your browser.