What is a Percentage Calculator?

A percentage is a ratio expressed as a fraction of 100. The word comes from the Latin per centum— meaning “per hundred.” Percentages appear in almost every area of daily life: a shop advertises 20 % off, a bank quotes a 4.5 % annual interest rate, a test is graded as 78 %, or a diet app shows that a meal covers 35 % of your daily calorie target. This tool handles the two most common percentage calculations so you never have to remember the formula.

The calculator supports two modes. X% of Yanswers questions like “What is 15% of 240?” — useful for discounts, tips, tax amounts, and commission values. A is what % of Banswers questions like “50 is what percent of 200?” — useful for comparing results, measuring progress, or expressing one quantity relative to another.

How to Use the Percentage Calculator

To find X% of Y: enter the percentage in the first field and the base value in the second field of the left card. The result updates instantly as you type.
To find what percent A is of B: enter the partial value (A) in the first field and the total value (B) in the second field of the right card. The result shows the percentage to four decimal places.
Both cards share the base value field — changing it updates both calculations simultaneously, which is handy when you are working with a fixed total and want to see multiple percentages at once.

The Maths Behind the Results

The two formulas used are straightforward:

X% of Y = (Y × X) ÷ 100. Example: 15% of 240 = (240 × 15) ÷ 100 = 36.
A as a % of B = (A ÷ B) × 100. Example: 50 as a percentage of 200 = (50 ÷ 200) × 100 = 25%.

Results are displayed to four decimal places to avoid rounding errors when the value is used in further calculations, for example when computing VAT-inclusive prices or apportioning budget lines. Round to two decimal places for money and whole numbers for counts.

Everyday Use Cases

Shopping discounts: A jacket costs €120 and is 30% off. Enter 30 and 120 into the X% of Y card — the discount is €36, so the final price is €84.

Restaurant tip: The bill is $85. Enter 18 and 85 to find an 18% tip of $15.30.

Test score:You answered 43 out of 56 questions correctly. Enter 43 and 56 into the “A is what % of B” card — your score is 76.7857%.

Budget tracking: You have spent €3,400 of a €12,000 project budget. 3400 ÷ 12000 × 100 = 28.33% used.

Frequently Asked Questions

How do I calculate a percentage increase?

Subtract the original value from the new value, divide by the original value, then multiply by 100. For example, a price rising from €80 to €92 is an increase of (92 − 80) ÷ 80 × 100 = 15%. This specific formula is not included in the current tool but can be derived using the “A is what % of B” card with the difference as A and the original as B.

Why does the result show four decimal places?

Four decimal places prevent premature rounding when the result feeds into a further calculation. If you only need a clean number, round to two decimal places for money or zero decimal places for whole-number counts.

What happens if I enter 0 as the base?

Dividing by zero is undefined in maths. The calculator returns 0% for the “A is what % of B” result when the base is 0, rather than showing an error, to keep the interface stable while you are still typing.

Can I use this for VAT calculations?

Yes. To find the VAT amount on a net price, use X% of Y with your VAT rate and the net price. For example, 19% of €500 = €95 VAT. To find what percentage tax was applied, use the A is what % of B card with the tax amount and the net price.