What each mode calculates
- X% of Y — multiplies the value by the percentage. For example, 15% of 200 is 30.
- X is what percent of Y — divides the part by the total and multiplies by 100. For example, 30 out of 120 is 25%.
- Percentage change — takes the difference between the new and old values, divides by the old value, and multiplies by 100. Going from 80 to 100 is a +25% change.
Frequently asked questions
How is percentage change calculated?
It's (new − old) ÷ |old| × 100. A positive result means an increase, a negative result means a decrease. Using the absolute value of the starting number keeps the sign correct even for negatives.
Why does a result show a dash (—)?
That happens when the total or starting value is zero — you can't take a percentage of zero, so the result is undefined. Enter a non-zero value and it updates instantly.
Can it show a negative percentage?
Yes. In the change mode, a drop from a higher to a lower value shows as a negative percentage, for example 100 to 80 is −20%.
Is my input saved or uploaded?
No. The calculator runs entirely in your browser. Nothing you enter is stored or sent to a server.