% Percentage Calculator
Of, change, increase and decrease percentages
How it works
Percentages are everywhere — tips, discounts, taxes, raises, test scores — but the three operations people need are always the same: finding a percentage of a number, finding what percentage one number is of another, and finding the percentage change between two numbers. This calculator handles all three, so you never have to wonder whether to multiply or divide again.
Under the hood, a percentage is just a fraction out of 100. Once you see 25% as "25 per 100" (or 0.25), every percentage problem becomes ordinary multiplication or division.
The formula
What is X% of Y? (X ÷ 100) × Y. What percentage is A of B? (A ÷ B) × 100. What is the percentage change from old to new? ((new − old) ÷ old) × 100 — a positive answer is an increase, a negative one a decrease. To add X% to a number in one step, multiply by (1 + X ÷ 100); to subtract X%, multiply by (1 − X ÷ 100).
Worked example
An 18% tip on an $84.50 restaurant bill: (18 ÷ 100) × 84.50 = 0.18 × 84.50 = $15.21. A $120 jacket at 25% off: $120 × (1 − 0.25) = $120 × 0.75 = $90. And a salary rising from $55,000 to $61,600: (61,600 − 55,000) ÷ 55,000 = 6,600 ÷ 55,000 = 0.12, a 12% raise.
Frequently asked questions
What is the difference between percent and percentage points?
If a rate rises from 10% to 15%, that is a 5 percentage point increase — but a 50% increase relative to where it started. Politicians and advertisers mix these up constantly; now you will not.
If a price goes up 10% then down 10%, is it back to the start?
No — it ends at 99% of the original. The 10% decrease applies to the already-increased price, so it takes a bigger bite in dollars. Sequential percentages never simply cancel.
How do I convert a decimal to a percentage?
Multiply by 100. A decimal of 0.12 is 12%, and 1.5 is 150% — which just means one and a half times the original.