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Percentage Calculator - Percent, Discounts and Change

Simple percentage calculator: percent of a number, sale price after a discount, share as a percent, and percent change.

Percent of a number

% of =

Sale price after a discount

%
You pay: You save:

What percentage?

of =

Percent change

=

How it works

Four everyday percentage calculations in one place: find a percentage of a number, work out a sale price after a discount, see what percentage one number is of another, and measure the percentage change between two numbers. Type in any field and the answers update live.

A quick reminder: "25% of 800" means 0.25 × 800 = 200. A "25% discount" on 800 means you pay 800 × 0.75 = 600 and save 200. The change from 800 to 600 is (600 - 800) / 800 = -25%. Everything is calculated locally in your browser.

About this tool

The percentage calculator does the four most common percentage jobs in one place: percent of a number, sale price after a discount, "what percentage is A of B", and percent change from A to B. Useful for shopping and sales, salary and raises, statistics, tax, returns, grade calculation, recipes, and anything else involving percent. All local, type in any field and see the answer update right away.

How to use it

  1. Choose which of the four modules you need.
  2. Enter the numbers in the fields.
  3. The answer updates automatically as you type.
  4. Copy the result directly from the screen.

Examples

Percent of a number
Input25% of 800
Output200
Sale price after discount
InputPrice 1200, discount 30%
OutputYou pay 840, saving 360
Common trap: two sequential 20% + 10% discounts do NOT give 30% total, but 28% (0.8 × 0.9 = 0.72 = 28% off). Percent calculations do not stack linearly.

Common use cases

  • Working out a tip at a restaurant or a service charge.
  • Checking "SALE" prices and comparing stores.
  • Calculating a raise in currency or new salary after a percentage rise.
  • Grade calculation, score calculation on tests and exams.
  • Statistics: how much did something change in percent since last year?

Frequently asked questions

What is the difference between percent and percentage points?
If a rate goes from 3% to 5%, the change is 2 percentage points, but 66.7% relative (2/3 = 0.667). A percentage point is an absolute difference between two percent values; percent change is relative to the starting point. Politicians and journalists often confuse these, so "the rate rose 2%" can mean either "from 3 to 5" or "from 3.00 to 3.06".
How do I find the price before a discount?
Divide the sale price by (1 - discount/100). Example: 840 after 30% off → 840 ÷ 0.7 = 1200 before discount. Useful for checking if "60% off" is real, or if the shop marked the original price up first. Consumer authorities in Norway (and the EU’s Omnibus directive) require the "before" price to be genuine.
How do I undo a percent change?
Not just by applying the same percent backwards! 100 → 120 (+20%) → 96 (−20%), a loss of 4. To reverse: if something rose by X%, it must fall by X / (100 + X) × 100% to return. +20% needs −16.67% back. This is why 10% stock-market "corrections" are not just quiet days.
Are my numbers private?
Yes. Everything runs in your browser in JavaScript. No numbers are sent to any server and we store nothing. Fine for work figures, budgets and other things you don’t want to share.

Technical background

Percent is just another way to write fractions with denominator 100: 25% = 25/100 = 0.25. The four modules use: (1) percent × number = p·x/100, (2) sale price = price × (1 - d/100), (3) A is (A/B × 100)% of B, (4) change = (new - old) / old × 100. All runs in IEEE 754 double-precision in the browser, with rounding at the 15th decimal (negligible for prices and statistics). Note the frequent confusion between percentage points and relative change: 3% → 5% is +2 percentage points or +66.7% relative. The calculator does the maths; correct interpretation is up to you.