How do you calculate a percentage?

Divide the part by the whole and multiply by 100, or multiply the whole by (percent ÷ 100). Example: 15% of 200 = 0.15 × 200 = 30.

Is this percentage calculator free?

Yes. PercentBox is free, works in your browser, and does not require an account.

Which mode should I open first?

If the sentence contains “what is __% of,” use percent-of. If it contains “what percent is A of B,” use the reverse mode. If you have two full measurements and want the growth between them, use percentage change — not percent-of.

Why do increase and change both exist?

Increase applies a rate you already know to one value. Change discovers the rate from two values. They meet only when you check your work: apply the rate you found and see if you land on the second value.

Does this page replace the dedicated calculators?

It uses the same formulas. The dedicated pages exist so a single question — a tip split, a VAT-inclusive price, a loan payment — gets a longer explanation than a tab label. Use this page to identify the question. Use the dedicated page when the question is already clear and the surrounding mistakes matter.

Why does the formula line change when I only change tabs?

Because the tab is the formula. The digits in the boxes are raw numbers until a formula claims them. A 15 and a 200 on percent-of mean 30. The same digits on the reverse tab mean 15 is 7.5% of 200. The formula line under the result is the authority, not the memory of the previous tab.

Are the results stored anywhere?

The calculation runs in the browser. An optional history list keeps a few recent summaries in local storage on this device. Clearing site data, or clearing history in the calculator, removes them. Nothing on this page requires an account.

What should I do with a percent that came from a percent?

Slow down. “20% of a 15% fee” is not 35% and not 5%. It is a percent of a percentage, a smaller piece of the original. The guide on that pattern walks through it. This calculator will happily multiply whatever you type, including a number that is already a rate.

Percentage Calculator

Use this free percentage calculator to solve everyday percent problems in seconds. Choose a mode, enter your numbers, and get an instant answer with the formula shown.

Written and maintained by Ricardo Rodrigues · Last updated October 7, 2026 · What changed

Who this calculator is for

This is the desk calculator: six modes, one page, and a formula line that changes when you change tabs. It is for the moment you have a percent problem and you are not yet sure which sentence it is. A student checking homework, a freelancer sanity-checking a quote, and someone splitting a bill can all start here. If you already know the sentence — “what percent is this of that,” “down by,” “from last month to this month” — the dedicated page for that sentence is the better teacher, because it stays on one formula.

The page will not decide the sentence for you. “15% of 200,” “200 increased by 15%,” and “from 200 to 230” are three different questions that can all be true of the same story. The tabs exist so you can see which one you are actually asking before you copy a number into an email.

What is X% of Y?

Find a percentage of a number

Percentage (X%)

Of number (Y)

Quick select

Result

Enter values to calculate

Comparison table

Quick reference: X% of Y
%	40	80	250	1200
5%	2	4	12.5	60
10%	4	8	25	120
15%	6	12	37.5	180
20%	8	16	50	240
25%	10	20	62.5	300
50%	20	40	125	600

Each column is one base. Reading across shows how the same percent scales with the base.

About this percentage calculator

This page is the multi-mode tool: percent of a number, the reverse question, increase, decrease, change, tip, and discount. The modes share a percent sign and do not share a base. “15% of 200” divides the percent by 100 and multiplies. “From 80 to 100” divides a gap by the starting value. Switching tabs changes the formula, not just the label.

If you already know which sentence you are in, a dedicated calculator below is harder to mis-type. If you are still translating a word problem into a sentence with the word “of,” stay here and read the formula line under the result before you copy it.

How to use each field

Mode tabs (% of, is % of, Inc / Dec, Change, Tip, Discount): Each tab is a different formula, not a skin. The page opens on “% of.” Switching tabs keeps whatever digits were already typed, which is convenient when you meant to stay in the same problem and dangerous when you did not. Read the title under the tabs after you switch. If it does not match the sentence in your head, you are about to answer a different question.
Percentage (X%) and Of number (Y): These two boxes are the “what is X% of Y?” mode. X is the rate. Y is the whole, the number after the word “of.” 15 and 200 produce 30. Quick-select buttons write a common rate into X and leave Y alone.
Number (X) and Is what % of (Y): On the reverse tab, X is the part you already have and Y is the whole you are comparing it with. 9 and 12 produce 75%. Y is the denominator. Zero in Y is undefined, and the page should not invent a percent.
Starting value, By percentage, and Direction: Increase / Decrease applies a rate you already know. Starting value is the base the rate sticks to. By percentage is the rate. Direction chooses add or subtract. 100 increased by 15% is 115. The same digits with Decrease are 85. The amount added or removed is shown beside the new total.
From and To: Percentage change does not take a rate as an input. From is the reference measurement, usually the earlier one. To is the later one. From 80 to 100 is a 25% increase. Swap them and you get a 20% decrease. The gap in units is 20 either way; the percent changes because the base changed.
Bill, tip, people, price, and discount: Tip multiplies the bill by the tip rate and divides the total by the headcount. Discount subtracts one percent-off from the original price and reports both what you pay and what you save. Those tabs are shortcuts. The tip and discount pages explain the customs and the stacked-offer mistakes in more detail.
Quick select, copy, and history: Quick select fills the percent box for the mode that has one. It does nothing useful on Change, which has no percent input. Copy puts the result on the clipboard. History keeps a short list of recent summaries in this browser only; it is not an account and it does not sync.

When to use this calculator

You are hopping between two kinds of percent question and want one place that shows the formula for the mode you picked.
You want a quick sanity check of mental math (10% anchors) against a live result.
You do not yet know whether you need a tip, a discount, or a plain percent-of.

Worked examples

Example calculations for Percentage Calculator
Question	Answer
What is 15% of 200?	30
What is 20% of 50?	10
What is 7.5% of 80?	6

Walkthroughs

A quote that looks like one problem and is three

A client says: “The draft was €800. We want 15% more scope, and the new total should be shown against the old one.” Start on Increase, not on percent-of. Starting value 800, by percentage 15, direction Increase. The new fee is 920, and the piece you added is 120. Percent-of would have stopped at 120 and left you quoting the raise instead of the fee.

Then check the story with Change: from 800 to 920. The result is 15% increase. That match is the point of having both tabs. If someone later says “15% of 800 was added,” that sentence is also true, and it is the percent-of tab: 120. Three sentences, three tabs, one project. Copy the one that matches the line in the proposal.

Why 10% anchors fail on the reverse tab

You remember that 10% of 200 is 20, so 20% is 40. That anchor lives on the percent-of tab. It does not answer “45 is what percent of 200.” Divide 45 by 200 and multiply by 100: 22.5%. The 10% anchor can still check the neighborhood — 45 is a bit more than 40, so a bit more than 20% — but the tab has to be the reverse one or the anchor is answering a different question.

Formula

Goal	Formula
X% of Y	(X ÷ 100) × Y
X is what % of Y	(X ÷ Y) × 100

Percent-of multiplies: (X ÷ 100) × Y. Reverse percent divides: (X ÷ Y) × 100. Increase multiplies by (1 + rate/100). Decrease multiplies by (1 − rate/100). Change divides the gap by the absolute value of the start: ((new − old) ÷ |old|) × 100. Tip is percent-of applied to a bill, then added back. Discount is a decrease, with the savings line called out separately.

A useful check is to run the reverse of what you just did, on purpose. If 15% of 200 is 30, then 30 should be 15% of 200 on the reverse tab. If 100 increased by 15% is 115, the change from 100 to 115 should also be 15%. When those disagree, a digit moved or a tab did. The formulas meet there. They are not interchangeable on the way in.

The calculator labels money fields with a dollar sign because the input needs a currency glyph. The arithmetic does not know whether you meant dollars, euros, or points. A percent of a count works the same way as a percent of a price. What changes is the sentence you are allowed to say afterward.

Mistakes this page will not catch for you

Leaving the previous mode’s numbers in place

A bill typed for a tip is not a meaningful “X is what percent of Y” pair. Clear the inputs when you change mode, or you will get a confident answer to a question you are no longer asking.

Reading 200% of as a 200% increase

200% of 50 is 100. A 200% increase of 50 is 150. The mode name is the difference. Percent-of keeps only the piece (which can be larger than the original). Increase keeps the original and adds the piece.

Letting Quick select rewrite a rate you typed on purpose

The buttons are for 5, 10, 15, 18, 20, and the other usual suspects. If you had typed 7.5 for a fee schedule, tapping 10 replaces it. The result updates immediately, with no calculate button to warn you. Glance at the percent box before you copy.

FAQ

How do you calculate a percentage?: Divide the part by the whole and multiply by 100, or multiply the whole by (percent ÷ 100). Example: 15% of 200 = 0.15 × 200 = 30.
Is this percentage calculator free?: Yes. PercentBox is free, works in your browser, and does not require an account.
Which mode should I open first?: If the sentence contains “what is __% of,” use percent-of. If it contains “what percent is A of B,” use the reverse mode. If you have two full measurements and want the growth between them, use percentage change — not percent-of.
Why do increase and change both exist?: Increase applies a rate you already know to one value. Change discovers the rate from two values. They meet only when you check your work: apply the rate you found and see if you land on the second value.
Does this page replace the dedicated calculators?: It uses the same formulas. The dedicated pages exist so a single question — a tip split, a VAT-inclusive price, a loan payment — gets a longer explanation than a tab label. Use this page to identify the question. Use the dedicated page when the question is already clear and the surrounding mistakes matter.
Why does the formula line change when I only change tabs?: Because the tab is the formula. The digits in the boxes are raw numbers until a formula claims them. A 15 and a 200 on percent-of mean 30. The same digits on the reverse tab mean 15 is 7.5% of 200. The formula line under the result is the authority, not the memory of the previous tab.
Are the results stored anywhere?: The calculation runs in the browser. An optional history list keeps a few recent summaries in local storage on this device. Clearing site data, or clearing history in the calculator, removes them. Nothing on this page requires an account.
What should I do with a percent that came from a percent?: Slow down. “20% of a 15% fee” is not 35% and not 5%. It is a percent of a percentage, a smaller piece of the original. The guide on that pattern walks through it. This calculator will happily multiply whatever you type, including a number that is already a rate.