Percentage Calculator
Calculate percentages, percentage change, and ratio. Runs on your device — nothing is uploaded, nothing is stored.
This percentage calculator puts the five calculations people actually look up on one page, each in its own card and all live at once. Work out what X% of a number is, what percentage one number is of another, the percentage change between an old and a new value, a number after adding and after subtracting a percentage, and the original value behind a total that already includes a percentage.
There is no calculate button. Fill in the two boxes in a card and its answer updates immediately; each card is independent, so you can use several without clearing anything. Percentage change reports both the size of the change and whether it is an increase or a decrease, along with the plain difference between the two numbers. The add-or-subtract card shows both outcomes side by side, which is handy for a price with and without a markup or discount.
Why this runs on your device
Honestly, a handful of numbers and a percentage are not sensitive, so privacy is not the point here. The benefit is that every card recalculates as you type, with no page reload and no account.
- Find the card that matches your question, such as percentage of a number or percentage change.
- Type the two numbers into its boxes.
- Read the answer shown under the boxes; it updates as you type.
- It does the arithmetic and nothing more: no rounding to currency, no tax or VAT presets, and no saved history. Results show up to four decimal places with trailing zeros removed.
- Empty boxes count as zero, so a card can show a result such as 0 before you have finished typing. Dividing by zero, for example a percentage change from an original value of 0, shows a dash instead of a number.
- The reverse card removes a percentage that was added. To undo a discount instead, enter the discount as a negative percentage, such as -20.
- Percentage change divides by the absolute value of the original number, so a move from -50 to -25 is reported as a 50% increase because the value went up.