Percentage Change Calculator
Enter an original value and a new value to see the percent increase or decrease between them.
How it works
Percentage change measures movement relative to a starting point, not a static “X is what percent of Y” relationship. A price that moves from 80 to 60 has fallen 25% of the original 80, even though 60 is 75% of 80. The formula divides by the absolute value of the original amount so a change from −50 to −40 is a 20% increase (the number became less negative).
Formula
Percentage change = ((new − old) ÷ |old|) × 100
Worked examples
- old 50, new 75 → 50% increase
- old 80, new 60 → 25% decrease
Useful notes
- A result of 0% means the two values are equal.
- If the original value is 0 and the new value is not, the change is undefined — you cannot divide by zero.
- This is not the same as a discount calculator, which applies a chosen percent off a price.
FAQ
- How do I calculate percentage increase?
- Subtract the original value from the new value, divide by the absolute original value, and multiply by 100. From 50 to 75 that is ((75 − 50) ÷ 50) × 100 = 50%.
- What if the original value is zero?
- If both values are zero, the change is 0%. If the original is zero and the new value is not, percentage change is undefined because the formula would divide by zero.
- Is percentage change the same as “what percent is X of Y”?
- No. “10 is what percent of 50” is a static ratio (20%). Percentage change asks how far you moved from the starting number.
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