Percentage Calculator — Percent Of and Change

What it is

Percentages show up all the time: sale prices, pay rises, test scores, growth figures, tips and fees. Nearly all of them come down to a handful of formulas. This calculator puts the seven most common ones on one page: B% of A, a part as a percent, percent change, sale price, the original price behind a sale price, increase or decrease by a percent, and the difference in percentage points. Change a number and the result updates immediately, and below it you see the formula filled in with your own values, so you can check how the answer was reached and reuse it in a spreadsheet.

How to use

1. Find the card that matches your question and type your numbers. Commas (1,250) and decimals (12.5) are fine.
2. The result and formula update as you type; there is no calculate button.
3. Press the copy button to take the result with you.
4. If an error appears, follow its hint and correct the number.

How it works

• B% of A: A × B ÷ 100. Negative numbers are calculated as they are.
• A as a percent of B: A ÷ B × 100. If B is 0 the answer does not exist.
• Percent change (A to B): (B − A) ÷ |A| × 100. Using the absolute value of A keeps the sign meaningful when you start from a negative number. If A is 0 the change is undefined.
• Sale price: original × (1 − rate ÷ 100); the amount saved is original × rate ÷ 100. The discount rate must be between 0 and 100.
• Original price from a sale price: sale ÷ (1 − rate ÷ 100). 35,000 after 30% off was 50,000 before, not 35,000 plus 30% (45,500). The rate must be at least 0 and below 100.
• Increase or decrease by B%: A × (1 + B ÷ 100); enter a negative B (−15) to decrease.
• Percentage points: the plain difference B − A between two rates. An interest rate falling from 3% to 2.5% is −0.5 pp, which is a relative change of about −16.7%.
• Display: results are rounded to 12 significant digits to remove binary floating-point noise, then shown with up to 6 decimals, so 0.1 + 0.2 reads as 0.3.
• Everything runs in your browser. Nothing you type is sent anywhere.

Examples

Question	Input	Result
B% of A	15% of 200	30
A as a percent of B	30 of 200	15%
Increase	80 to 100	+25%
Decrease	100 to 80	−20%
Sale price	50,000 with 30% off	35,000 (saves 15,000)
Decimals	7% of 19.99	1.3993
Original price	35,000 after 30% off	50,000
Increase	10,000 up 30%	13,000
Percentage points	32.5% to 41%	+8.5 pp (+26.15% relative)