Percentage Calculator
Three modes: find X% of Y, X is what % of Y, and percentage change from A to B.
Percentages are everywhere — discounts, tips, tax, interest, exam scores, statistics — yet they trip up almost everyone at some point, especially when the question is phrased in an unfamiliar way. This calculator handles the three percentage problems that come up most often: finding X% of a number, working out what percentage one number is of another, and calculating the percentage change between two values.
Each of these answers a different everyday question. "What is 15% of $80?" sizes up a tip. "45 is what percent of 60?" turns a test score into a grade. "Prices went from $50 to $65 — what's the increase?" measures change. By laying out all three modes clearly, the tool removes the guesswork about which calculation you actually need, and the page below explains the simple logic behind each so you can do them in your head when a calculator isn't handy.
Plug in some numbers —
we'll crunch.
How to use
- 1Select the mode that matches your question.
- 2Enter the two numbers.
- 3'What is X% of Y?' — finds a percentage of a number (e.g. 15% of 200 = 30).
- 4'X is what % of Y?' — finds what percentage one number is of another.
- 5'% change from A to B' — calculates percentage increase or decrease.
How it works
A percentage is just a fraction out of 100, so 'percent' literally means 'per hundred'. To find X% of a number, convert the percentage to a decimal (divide by 100) and multiply: 15% of 80 is 0.15 × 80 = 12. To find what percentage one number is of another, divide the part by the whole and multiply by 100: 45 of 60 is 45 ÷ 60 × 100 = 75%.
Percentage change measures how much a value grew or shrank relative to where it started: (new − old) ÷ old × 100. A jump from 50 to 65 is (65 − 50) ÷ 50 × 100 = 30% increase. The key subtlety is that the denominator is always the original value — a common source of error is mixing up which number you started from, which flips the result and changes its size.
Worked examples
Finding a percentage of a number
An item costs $80 and is marked 25% off.
- Convert: 25% = 0.25.
- Multiply: 0.25 × 80 = $20 discount.
- Final price = 80 − 20 = $60.
The discount is $20, leaving a sale price of $60. A quick mental check: 25% is one quarter, and a quarter of $80 is $20.
Percentage change — and why direction matters
A stock falls from $200 to $150, then recovers to $200.
- The drop: (150 − 200) ÷ 200 × 100 = −25%.
- The recovery: (200 − 150) ÷ 150 × 100 = +33%.
A 25% fall needs a 33% rise to get back to where it started, because the second calculation divides by the smaller number. This asymmetry surprises people and matters in investing.
Tips & common mistakes
The most common percentage mistake is dividing by the wrong number in percentage-change problems. The denominator is always the original (starting) value, never the new one. Mixing them up is exactly why a 25% loss and a 25% gain don't cancel out.
Watch out for percentage points versus percent. If an interest rate rises from 4% to 5%, that is a one-percentage-point increase but a 25% relative increase. News headlines and arguments often blur these two, making changes sound bigger or smaller than they are — being precise about which you mean prevents real confusion.
Use mental shortcuts to sanity-check the calculator: 10% is just moving the decimal one place left, 50% is half, 25% is a quarter, and 1% is two places left. You can also reverse percentages — 15% of 80 equals 80% of 15 — which sometimes makes the arithmetic easier. These tricks catch the occasional fat-fingered input before it leads you astray.
Frequently asked questions
Last reviewed: June 2026
About this calculator
Three modes: find X% of Y, X is what % of Y, and percentage change from A to B.