About this calculator
Percentage questions trip people up because the base matters. A 20% rise and a 20% fall do not cancel out: falling 20% from 100 leaves 80, and rising 20% from 80 gives 96, not 100. That asymmetry comes from always dividing by the base.
How it works
This calculator shows the formula for whichever calculation you choose, so the answer is auditable rather than a black box. It covers the six forms of percentage question that come up in everyday money and business decisions.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For 15% of 250, that is 250 × 0.15 = 37.5.
Why is a 20% drop not cancelled by a 20% rise?
Because each percentage uses a different base. From 100, a 20% drop leaves 80. A 20% rise on 80 gives 96, which is below the original 100.
What is the difference between percent change and percent difference?
Percent change describes a movement from an original value and uses the original as the base. Percent difference compares two values with no original and uses the average as the base.
How do I calculate a 15% tip?
Multiply the bill by 0.15. On a $60 bill that is $9, giving a total of $69. For quick mental maths, 10% is a tenth and 5% is a twentieth, so 15% is a tenth plus a twentieth.
What is a good percentage for a salary raise?
Typical annual raises run 3 to 5%, with larger increases for a promotion or a job change. A raise of your own rate compounds, so three 5% raises total about 15.8%.
How do I calculate a percentage increase in price?
Multiply the original price by one plus the increase rate. Raising 40 by 10% gives 44. To reverse a 10% increase, you must divide by 1.10, not subtract 10%, because 44 less 10% is 39.60.