How to use the percentage calculator
This calculator offers three modes. Mode 1 finds X% of a value — for example, 20% of 150 = 30. Mode 2 finds what percentage one number is of another — for example, 30 is 20% of 150. Mode 3 calculates the percentage change between two values — for example, going from 80 to 100 is a +25% increase. Fill in the two inputs in any section and the result appears instantly.
Percentage formulas
The three core formulas: (1) X% of Y = (X / 100) × Y. (2) What % is A of B = (A / B) × 100. (3) % change from A to B = ((B − A) / |A|) × 100. A positive result in mode 3 means an increase; a negative result means a decrease.
Frequently Asked Questions
What does a negative percentage change mean?
A negative result in the percentage change calculator means the value decreased. For example, going from 100 to 80 is a −20% change. Going from 80 to 100 is a +25% change — note the asymmetry: the base value is different.
How many decimal places are shown?
Results are rounded to four significant decimal places to avoid floating-point noise while still showing meaningful precision. Copy the result and round further as needed.