Percentage calculator
This percentage calculator handles the three most common percentage tasks at once: what a given percentage of a number is, what portion one number is of another as a percentage, and by how many percent a value has changed. Results are computed instantly right in your browser, so there is nothing to upload and nothing to install.
How the percentage calculator works
A percentage expresses a ratio relative to a base of 100. The notation 20% means twenty hundredths, that is 0.20. Our calculator runs three separate, independent rows, and each uses a different formula:
- What is A% of B — multiplies the base by the percentage fraction:
A × B ÷ 100. - A is what % of B — finds the ratio and converts it to a percentage:
A ÷ B × 100. - Percentage change from A to B — computes the difference relative to the original value:
(B − A) ÷ A × 100. A positive result means growth, a negative one a decline.
Every result is rounded to two decimal places. The change is shown with a sign (for example +25% or −12.5%) so you can immediately tell the direction.
How to use the percentage calculator
- Choose the row that matches your question (percentage of a number, share as a percentage, or change).
- Type your numbers into the fields — the result recalculates instantly on every keystroke, no button needed.
- Leave the other rows alone, or use them for a parallel calculation.
An example of inputs and results:
| Input | Formula | Result |
|---|---|---|
| What is 20% of 150 | 20 × 150 ÷ 100 | 30 |
| 30 is what % of 120 | 30 ÷ 120 × 100 | 25% |
| Change from 100 to 125 | (125 − 100) ÷ 100 × 100 | +25% |
What the percentage calculator is good for
You run into percentages almost daily, and this calculator covers the typical situations:
- Discounts and prices — how much you save at 30% off or the final price after a discount.
- VAT and markups — adding or removing tax and margin.
- Tips and splitting — how much to add to a restaurant bill.
- Year-over-year comparison — by how many percent revenue, website traffic, or costs grew.
- School and tests — what percentage of the maximum points you scored.
Because the whole calculation runs locally in your browser, none of the numbers you enter leave your device — nothing is uploaded to a server, and the tool works offline once the page has loaded.
FAQ
How do I calculate what a given percentage of a number is?
Use the first row: enter the percentage and the base. The calculator multiplies the base by the percentage fraction using A × B ÷ 100. For example, 20% of 150 is 30.
How do I find what percentage one number is of another?
Use the second row. The calculator divides your number by the base and multiplies by one hundred: A ÷ B × 100. For example, 30 out of 120 is 25%.
How is percentage change or increase calculated?
The third row uses the formula (new − original) ÷ original × 100. A positive number is an increase, a negative one a decrease. A change from 100 to 125 is +25%.
Why does the change show a plus or minus sign?
The sign shows direction: <strong>+</strong> means the value went up, <strong>−</strong> means it went down. This lets you tell at a glance whether the number rose or fell.
How precisely are results rounded?
Each result is rounded to two decimal places. For most everyday calculations (prices, discounts, taxes) this is entirely sufficient.
Are my numbers sent to any server?
No. The entire calculation runs directly in your browser using JavaScript. No value you enter leaves your device, and the tool works even without an internet connection.
What if I enter zero as the base?
Division by zero has no valid result, so the second and third rows show a dash instead of a number. Enter a non-zero base for the ratio to make sense.
How do I work out the price after a discount?
First use the first row to calculate the discount itself (e.g. 30% of 800 = 240), then subtract that amount from the original price. The final price is 800 − 240 = 560.
📅 Last updated: 11 July 2026