Percentage Calculator
Calculate percentages instantly — find X% of a number, percentage change, and more.
Percentage Calculator is a fast, browser-based tool that solves the four most common percentage problems in one click. It is useful for students checking scores, shoppers calculating discounts, accountants applying markup or tax, and anyone who needs a quick answer without opening a spreadsheet. All calculations run directly in your browser — nothing is sent to a server.
Tool interface
The interface is organized into four tabs, one for each calculation type:
- % of Number — enter a percentage and a number to find the result (e.g. 25% of 200 = 50)
- X is what % of Y — express one value as a percentage of another (e.g. 50 out of 200 = 25%)
- % Change — enter an original value and a new value to find the increase or decrease
- Add / Subtract % — apply a percentage markup or discount to any number
Each panel shows the result instantly with a plain-English summary below the value. Switch between tabs at any time — each panel keeps its own inputs.
Percentage formulas
| Calculation | Formula | ||
|---|---|---|---|
| X% of Y | result = (X / 100) × Y |
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| X is what % of Y | result = (X / Y) × 100 |
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| % increase or decrease | `change = ((new − old) / | old | ) × 100` |
| Add X% | result = number × (1 + X / 100) |
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| Subtract X% | result = number × (1 − X / 100) |
Common use cases
- Shopping — find the discount amount before confirming a purchase
- Finance — apply VAT, sales tax, or a markup to a price
- School — convert a raw score to a percentage grade
- Analytics — measure growth or decline between two period values
- Salary — calculate what a raise or pay cut is as a percentage
FAQ
What is X% of a number?
Multiply the number by X then divide by 100. For example, 25% of 200 equals (25 / 100) × 200 = 50. The % of Number tab calculates this directly.
How do I find what percentage X is of Y?
Divide X by Y and multiply by 100. For example, 50 out of 200 equals (50 / 200) × 100 = 25%. Use the X is what % of Y tab for this.
How is percentage change calculated?
Subtract the original value from the new value, divide by the absolute value of the original, then multiply by 100. A positive result means an increase; a negative result means a decrease. The % Change tab shows increases in green and decreases in red.
How do I add or subtract a percentage from a number?
To add X%: multiply the number by (1 + X / 100). To subtract X%: multiply by (1 − X / 100). For example, adding 20% to 500 gives 500 × 1.20 = 600. The Add / Subtract % tab handles both operations with a dropdown for the direction.
Is this calculator accurate?
Yes. It uses standard JavaScript floating-point arithmetic and displays up to 10 significant digits. For everyday calculations the result is exact. Very large or very small numbers follow standard IEEE 754 double precision behaviour.