Solve everyday percentage problems in seconds with this Percentage Calculator
Percentages turn up everywhere — a discount in a shop, the tip at the end of a meal, the interest on a savings account, your score on a test, the VAT or sales tax on an invoice, or how much a price has risen since last year. This percentage calculator handles the three questions that cover almost all of those situations: what is a percentage of a number, what percent one number is of another, and how much a value has gone up or down. You type your two numbers and the answer appears straight away, complete with the working written out so you can check it or copy it into homework or a report.
It is built for anyone who would rather not reach for a phone calculator and start juggling the ÷ 100 step in their head. Students checking marks, shoppers sizing up a sale, freelancers adding tax to a quote, and anyone splitting a bill can all get a clean answer here. There is nothing to install and no account to create, everything runs in your browser on the device in front of you, and the layout is sized so the buttons and inputs stay easy to tap on a small phone screen.
How to use it
- Choose a mode at the top: % of a number, X is what %, or % change.
- Type your two numbers into the boxes — decimals and negative numbers are fine.
- The result updates as you type; there is no calculate button to press.
- Read the highlighted answer and the one-line working underneath it.
- Switch modes any time — the calculator keeps the numbers you have already entered.
The three modes, and which one to pick
Use % of a number when you know a percentage and want the actual amount — for example 20% of a 150 bill, the size of a 15% tip, or how many of 500 students passed. Use X is what % when you have two real amounts and want the percentage between them — 30 marks out of 150, or 45 sales out of a target of 60. Use % change when you want to compare an old value with a new one — a price moving from 100 to 150, your weight last month versus this month, or last year's revenue against this year's. The difference matters: "20% of 150" and "what percent is 30 of 150" use the same numbers but answer completely different questions.
The simple formulas behind it
The maths is short and worth knowing. To find a percentage of a number, multiply the number by the percentage and divide by 100 — 20% of 150 is 150 × 20 ÷ 100 = 30. To find what percent one number is of another, divide the first by the second and multiply by 100 — 30 ÷ 150 × 100 = 20%. To find a percentage change, subtract the original from the new value, divide by the original, then multiply by 100 — from 100 to 150 is (150 − 100) ÷ 100 × 100 = a 50% increase, while 150 down to 120 is a 20% decrease. The calculator colours an increase green and a decrease red so the direction is obvious at a glance.
Common mistakes to avoid
The biggest trap is the base of a percentage change: the percentage is always measured against the original value, not the new one. Going from 100 to 150 is a 50% rise, but going back from 150 to 100 is a 33.3% fall, not 50% — because the starting point changed. A second trap is assuming percentages reverse: a price cut by 20% then raised by 20% does not return to where it started, because the second 20% is taken from a smaller number. It is also easy to mix up "percent" and "percentage points" — moving from 10% to 15% is a 5 percentage-point change but a 50% relative increase. When you keep an eye on which number is the base, these mix-ups disappear.
Accuracy and privacy
Results are rounded to six decimal places, which is more than enough for money, marks, and everyday figures. Dividing by zero is handled for you — the calculator will ask for a non-zero number rather than show a broken result. Because all the calculation happens locally in your browser, nothing you type is sent to a server, saved, or shared; close the tab and the numbers are gone. That makes it safe to use for private figures like salaries, grades, or business numbers.