Percentage Calculator

Percentages, explained simply

A percentage is just a way of describing a part of a whole where the whole is always counted as one hundred. The word comes from the Latin per centum, meaning "for each hundred". When a shop says an item is 25% off, it is telling you that for every hundred units of price, twenty-five are being taken away. Because everything is scaled to the same base of one hundred, percentages let you compare things that would otherwise be hard to line up — a discount on a small purchase and a discount on a large one, a test score out of forty and another out of sixty, or the growth of two very different businesses.

This calculator brings together the three percentage questions people ask most often, so you never have to remember which formula goes where. Each section works on its own, updates the moment you type, and keeps everything inside your browser. Nothing you enter is sent anywhere, saved, or used to track you.

The three tools on this page

Percentage of a number. The first box answers the classic question "what is P percent of N?" Type the percentage into the first field and the number into the second, and the result appears instantly. This is the calculation behind sales discounts, tips, tax, commissions and almost any "take this share of that amount" situation.

One number as a percent of another. The second box answers "this value is what percent of that value?" Enter the part in the first field and the whole in the second. It is the tool you want when you have a score, a count or an amount and you need to express it as a percentage — for example, working out that 18 correct answers out of 24 questions is 75%.

Percentage increase or decrease. The third box compares an original value with a new one and tells you how much it changed in percentage terms. Enter where you started and where you ended up. A positive answer means the value went up, and a negative answer means it went down. This is exactly how price changes, salary rises, population growth and investment returns are usually described.

How each calculation works

To find a percentage of a number, divide the percentage by one hundred and multiply by the number. For example, 20% of 150 is 0.20 × 150 = 30. It helps to remember that "percent" literally means "divide by a hundred", so 20% is simply another way of writing 0.2.

To express one number as a percentage of another, divide the first number by the second and multiply by one hundred. So 18 out of 24 is 18 ÷ 24 × 100 = 75%. If the result is more than 100%, that simply means the first number is larger than the second — 30 out of 20 is 150%, which is perfectly valid.

To calculate percentage change, subtract the original value from the new value, divide by the original value (ignoring its sign), and multiply by one hundred. Going from 40 to 50 is (50 − 40) ÷ 40 × 100 = 25%, an increase. Going from 50 to 40 is (40 − 50) ÷ 50 × 100 = −20%, a decrease. Notice that the same ten-unit gap gives different percentages depending on where you started, which is one of the most common sources of confusion with percentages.

Everyday examples

Percentages turn up far more often than most people notice. When you leave an 18% tip on a 60 restaurant bill, you are finding a percentage of a number: 0.18 × 60 = 10.80. When a phone that cost 900 is on sale for 720, the percentage change tells you the discount is (720 − 900) ÷ 900 × 100 = −20%, so you are saving a fifth. When a student scores 42 out of 50 on an exam, expressing it as a percentage gives 84%, which is far easier to compare against other results than the raw marks.

The same maths applies to money and business. Interest rates, sales tax, profit margins, markups, and the returns on an investment are all percentages. Being comfortable moving between a raw amount and its percentage form is one of the most useful everyday numeracy skills there is, and it is exactly what the three tools above are designed to make effortless.

A few things worth remembering

Percentages do not simply add up in the way it feels like they should. If a price rises by 10% and then falls by 10%, you do not end up back where you started. Say something costs 100: a 10% rise takes it to 110, and a 10% fall from 110 removes 11, leaving 99. The second percentage is taken from a different, larger base, so the two changes do not cancel out. This is why the third tool always asks for the actual starting and ending values rather than a single percentage.

It is also worth keeping the difference between percentage points and percent clear. If an interest rate moves from 4% to 6%, that is a rise of two percentage points, but it is a 50% increase relative to the original 4%. Both statements are correct; they just measure different things. When you read news about rates, taxes or poll numbers, noticing which one is being used will help you avoid a very common misunderstanding.

Finally, remember that a percentage on its own can hide the size of what it describes. A 50% increase sounds dramatic, but 50% of a tiny number is still tiny, while a 5% increase on something enormous can be a huge amount in absolute terms. Whenever a percentage matters, it is worth glancing at the underlying quantities too. The calculator above shows both the numbers you enter and the percentage they produce, so you always keep sight of both sides.

Using the calculator

Pick whichever of the three tools matches your question, type your two numbers, and read the answer as it appears. There is no submit button and nothing to reset — just change a value to try another calculation. Results are rounded to two decimal places and formatted for your language so they are easy to read, while the calculation itself keeps full precision behind the scenes. Because it all runs locally, it works offline and responds instantly, making it handy whether you are checking a shop discount, marking a test, or working through homework.