Percentage change calculator
Old value in, new value in, and you get the percentage increase or decrease with its direction, plus the trap most people fall into, explained.
Guide
How to use it
- Put the old value first and the new value second. Order matters.
- Read the tile: the size of the change and whether it is an increase or a decrease.
- Check the note underneath for the absolute change and the return-journey percentage.
Examples
Worked examples
(1.56 − 1.42) ÷ 1.42 × 100 = 9.86% increase. Small unit prices produce big-feeling percentages.
(449 − 649) ÷ 649 × 100 = 30.82% decrease. Useful for checking whether a claimed sale discount is real.
A 148% increase. More than 100% simply means it more than doubled.
Method
How it works
Change = (new − old) ÷ old × 100. The old value is the base, which is why direction matters and why a rise and the fall that undoes it have different percentages. The tool prints the return journey under every result so that asymmetry never catches you out.
Runs entirely in your browser, nothing you type is sent anywhere.
FAQ
Frequently asked questions
What is the percentage change formula?
New value minus old value, divided by the old value, times 100. A positive result is an increase, a negative one a decrease.
Which number goes first?
The old value is the base. From 80 to 100 is a 25% increase. Swap them and you get a 20% decrease, which is a different question.
Why do increase and decrease percentages differ for the same numbers?
Each direction measures against its own starting point. 80 to 100 is +25% because the base is 80; 100 back to 80 is −20% because the base is 100. The tool shows the return journey under every answer.
Can percentage change be more than 100%?
Yes. From 40 to 100 is a 150% increase. Anything more than doubling is over 100%.
What if the old value is zero?
Percentage change from zero is undefined, you cannot divide by zero. Report the absolute change instead, or start from the first non-zero value.
Is this the same as percentage difference?
Not quite. Percentage difference compares two values symmetrically against their average, with no direction. Percentage change measures movement from old to new, which is what prices, pay and traffic reports mean.
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