How to use the Percentage Calculator
- Choose the calculation you need using the tabs: percentage of a number, what percent X is of Y, percentage increase, or percentage decrease.
- Enter your values into the fields — the result updates instantly as you type.
- Read the result and supporting figures in the panel on the right.
Formula
Percentage of a number:
(percentage ÷ 100) × number
X is what % of Y:
(X ÷ Y) × 100
Percentage change:
((new − old) ÷ |old|) × 100
(percentage ÷ 100) × number
X is what % of Y:
(X ÷ Y) × 100
Percentage change:
((new − old) ÷ |old|) × 100
Worked example
What is 15% of 240?
(15 ÷ 100) × 240 = 36
If a $50 item rises to $65, the percentage increase is ((65−50)÷50)×100 = 30%.
What this number means
A percentage expresses a number as a fraction of 100. It's the same underlying math whether you're calculating a tip, a grade, a discount, or a raise — only the labels change. Percentage increase and decrease always divide by the original value, not the new one, which is the detail most people get wrong.
Common mistakes
- Dividing by the new value instead of the original when calculating percentage change.
- Forgetting that a 50% decrease followed by a 50% increase does not return you to the original number.
- Mixing up 'percent of' with 'percentage points' — a change from 40% to 50% is a 10 percentage-point increase, but a 25% relative increase.
Frequently asked questions
How do I calculate a percentage increase?+
Subtract the original value from the new value, divide by the original value, then multiply by 100. A negative result means a decrease.
What's the difference between percentage and percentage points?+
Percentage measures relative change (e.g. a 25% increase), while percentage points measure the raw difference between two percentages (e.g. going from 40% to 50% is 10 percentage points).
Can a percentage be negative?+
Yes — a negative percentage typically represents a decrease, such as a loss or a drop in value.