Percentage Calculator

Calculate percentage of a number, what percent X is of Y, and change

What is it and how does it work?

A percentage calculator answers the three questions that come up constantly but are easy to fumble in your head: what is X% of a number, what percent one number is of another, and how much something changed in percentage terms. "What is 15% of 80?", "37 is what percent of 200?" and "the price went from 50 to 65 — what increase is that?" are different calculations, and mixing them up is the usual source of mistakes. This tool keeps them separate so you pick the question and get the right answer.

The maths behind each is simple but worth understanding: a percentage is just a fraction of 100, so 15% of 80 is 0.15 × 80, and a percentage change is the difference divided by the original value. The trap most people fall into is percentage change being asymmetric — a rise from 50 to 65 is a 30% increase, but going back from 65 to 50 is only a 23% decrease, because the base changed. This tool computes each correctly and runs entirely in your browser.

Common use cases

• Working out a discount or tip: find 20% of a bill to leave a tip, or 30% off a price during a sale.
• Calculating a change: see the percentage increase or decrease between an old and new value, such as a price or a score.
• Finding a proportion: work out what percent one figure is of another, like 37 correct answers out of 200 questions.

Frequently asked questions

How do I calculate what percent one number is of another?

Divide the part by the whole and multiply by 100. So 37 out of 200 is (37 ÷ 200) × 100 = 18.5%. This tool does it for you — enter the two numbers and it returns the percentage directly.

Why is a percentage increase not the reverse of the decrease?

Because the base changes. Going from 50 to 65 is a 30% rise (15 ÷ 50), but going back from 65 to 50 is a 23% drop (15 ÷ 65). The same absolute change is a different percentage when measured against a different starting value.

What is the difference between percentage points and percent?

A change from 10% to 15% is a rise of 5 percentage points, but a 50% increase in relative terms (5 ÷ 10). They answer different questions, and confusing them is a common error when discussing rates and statistics.

How do I add or remove a percentage from a price?

To add 20%, multiply by 1.20; to remove 20%, multiply by 0.80. Note that removing a percentage you previously added does not return the original number unless you reverse the exact factor — a common pitfall with tax-inclusive prices.

Math

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