Percentage Calculator
It answers the three standard percentage questions: X% of Y, percentage change from A to B, and A as a percentage of B.
15.00% of 240.00
36.00
What it calculates
It answers the three standard percentage questions: X% of Y, percentage change from A to B, and A as a percentage of B.
Why it matters
Percentages underpin discounts, tax, interest, tips, grades and statistics — and they are the most commonly mis-calculated everyday math.
Who it's for
Shoppers, students, analysts and anyone comparing before-and-after numbers.
Formula
- X%
- The rate applied
- Y
- The base value
Worked example
Price rises from 80 to 96
- 1Difference = 96 − 80 = 16
- 2Divide by the original: 16 ÷ 80 = 0.2
- 3× 100
A 20% increase
How the percentage calculator works
Percent of: (X ÷ 100) × Y. Percentage change: ((new − old) ÷ old) × 100. Share: (A ÷ B) × 100. The base always goes on the bottom — that is where most errors come from.
These three variants cover almost every percentage question asked online: taking a percentage of a number, expressing one number as a percentage of another, and measuring change between two values.
A negative result in change mode means a decrease. Note that a 50% drop needs a 100% rise to get back to where it started.
Common mistakes
- Reversing a percentage increase with the same percentage decrease — +20% then −20% does not return to the start.
- Dividing by the new value instead of the original when calculating change.
- Confusing percentage points with percent (a rise from 4% to 6% is 2 points, or 50%).
Tips and best practice
- To remove a 20% markup, divide by 1.2 rather than subtracting 20%.
- X% of Y always equals Y% of X — handy for mental math.
Frequently asked questions
How do I calculate percentage increase?
Subtract the old value from the new, divide by the old value, then multiply by 100.
What is the difference between percent and percentage points?
Points measure absolute difference between two percentages; percent measures relative change.
How do I reverse a percentage?
Divide by (1 + rate). A price of 120 after a 20% increase started at 120 ÷ 1.2 = 100.
How do I work out a percentage discount?
Multiply the price by (1 − discount/100), or use the discount calculator for savings and final price together.
Related calculators
Further reading
Methodology & trust
- Formula source
- Elementary arithmetic definitions of percentage.
- Last updated
- 2026-07-28
- Privacy
- Every calculation runs in your browser. No inputs are sent to a server or stored.
- Accessibility
- Keyboard navigable, labeled inputs and WCAG AA color contrast.