Percentage Calculator — Percent Of, Change and Discount
What is X% of a number
A is what percent of B
Percent change between two values
Percent and percentage points are different things. An interest rate that moves from 2% to 3% is up one percentage point — and at the same time up 50%, because 1 is half of 2.
Discount on a price
Up 20% and then down 20% does not return to the start: 100 → 120 → 96. The second percentage works on a bigger number.
Results are shown rounded to 2 decimal places. The arithmetic itself keeps every digit, so nothing drifts.
The numbers stay in your browser and are never sent anywhere.
About the Percentage Calculator
Four percentage questions on one page: what is X% of a number, what percent one number is of another, how much a value rose or fell, and what a price becomes after a discount. Each panel is a single question worded the way you would say it. The answer appears as you type, and a line under it shows the exact arithmetic — 80 × 15 ÷ 100 = 12 — so you can check the recipe instead of trusting a black box.
Two ideas cause most everyday percentage mistakes, and both are built into the page. A rate that moves from 2% to 3% is up one percentage point and at the same time up 50% — the change panel labels which reading is which. And a rise does not cancel an equal fall: up 20% then down 20% turns 100 into 96, because the second percentage bites on a bigger number.
A few inputs are refused instead of guessed at: a whole of zero, since no number is a percentage of nothing, and a percent change that starts at zero or below, where no single agreed answer exists. Results are shown rounded to two decimal places while the arithmetic underneath keeps every digit.
How to use it
- Say the question in words first — what is 15% of 80, 12 is what percent of 60, from 250 to 310, 30% off 45 — and the wording points at the right panel. Each panel is one of those four sentences.
- Use the first panel for tips, taxes and fees: the bill is the number, the rate is the percent. A handy shortcut hides here too — 15% of 80 and 80% of 15 both give 12.
- In the second panel order matters: the part goes first, the whole second. The part may be bigger than the whole — 30 of 24 is 125%, and that is a legitimate answer, not an error.
- Read percent change left to right, old value to new. Swapping the two gives a different percentage, and the note under the result explains why the directions disagree.
- In the discount panel read both output lines — what you pay and what you save. The two always add back to the original price, which is a quick way to check a price tag.
Questions
Is the Percentage Calculator free, and do I need an account?
Free, and there is no account. The arithmetic runs in your own browser, so there is nothing to sign up for — the numbers never leave the page.
Why use this instead of a spreadsheet or a search box?
You do not have to remember a formula, and the arithmetic is shown back to you. In a spreadsheet like Excel, a percent problem still depends on you writing the right expression yourself — and the wrong one looks just as tidy. A search-box calculator gives one number and does not say what it computed. Here each panel already is the question, worded in plain language, with the worked line printed under the answer.
What is a percentage point?
A percentage point is the plain difference between two percentages. When an interest rate moves from 2% to 3%, it is up one percentage point — and at the same time up 50%, because 1 is half of 2. News reports mix the two constantly, which is why the change panel here spells out both readings.
Why doesn't a 20% rise cancel a 20% fall?
Because the second percentage is taken of a different number. Start at 100: up 20% is 120, and 20% of 120 is 24, so down 20% lands on 96, not 100. To undo a rise of 20% you would need a fall of about 16.67%.
How are results rounded?
The display rounds to two decimal places; the arithmetic underneath keeps every digit. A result that shows as 33.33% was computed from the full value, and the rounding never feeds back into the calculation.
Why can't the whole be zero?
Because asking what percent 5 is of 0 means dividing 5 by 0, and that operation has no answer — not a huge number, no number at all. The tool refuses the input and says why, rather than printing something confident and wrong.
Why does percent change refuse to start from zero or a negative number?
Because the conventions disagree and every choice misleads someone. From 0 to any number the increase is infinite — dividing by zero again. From -10 to 10, one convention counts it as up 200% and another says a sign-crossing ratio has no meaning. Rather than silently picking a side, the calculator asks you to start from a positive value.
Can it work out loan interest or investment returns?
No, and that is a decision rather than a gap. This page does plain percentage arithmetic — of, out of, change and discount — and those four answers are pure math with one right result. Interest and returns are not: they depend on compounding periods, fees and terms, and turning them into advice for your situation is exactly what a general calculator should not pretend to do.