Free Online Calculators: Percentages and Everyday Maths

Calculators

Percentages, discounts and tips, loans and compound interest, health measures, and the odds behind a draw: the arithmetic you would otherwise redo three times on a phone calculator, with no record of which attempt was right.

Percentages

Percentages: four questions, not one

"Percentage" is four different sums wearing the same word. What is 15% of 240? 36 is what percentage of 240? A value that went from 36 to 54 changed by what percentage? And what is 240 increased by 15%? They look alike and produce four different answers, and a calculator that assumes you meant one of them is how the wrong number ends up in a document.

The percentage calculator asks which of the four you mean and shows the working, so the answer can be checked by hand. It also keeps apart the two things people mix up most: a change of two percentage points and a change of two percent. Going from 4% to 6% is both — a rise of two points and a rise of half — and which sentence is true depends on what is being measured.

Why there are no rate tables on these pages

None of these calculators contains a tax rate, an interest rate, a salary benchmark, a unit price or any other table of real-world numbers. That is a deliberate limit rather than a missing feature. A rate table is only useful if you can check where it came from and when it was true, and we have not found sources we would be willing to cite — let alone keep current.

So the calculators take the numbers you already have, from your own payslip, loan offer, recipe or form, and do the arithmetic in full view. The consequence is worth stating plainly: they will tell you what an 18% annual rate compounds to over four years, and they will not tell you whether the loan is a good idea. That second question depends on your income, your alternatives and the terms in the contract, and no calculator on the internet knows them.

Why a browser is the right place for this arithmetic

The sums in this category are pure functions of what you type, so there is nothing for a server to add except a copy of your numbers and a bill for running them. Every calculator here runs in the page you already loaded: nothing is sent anywhere, nothing is logged, and there is no usage limit, because a calculation that stays in your browser costs us nothing to run.

It also means the pages work with no connection once loaded, which matters more than it sounds for the ones people reach for on a phone in a shop or a bank branch. The single exception on the whole site is the ATS keyword check in the career category, which needs a language model and therefore runs on our server and is rate limited. We would rather say that out loud than hide a limit behind a vague error message.

Which one do you need?

• What is 15% of this number? Use the percentage calculator — that is the first of its four questions.
• This number went from 40 to 55 — what is the percentage change? The same tool, third question. Check whether you want the change as a percentage or as percentage points before quoting it.
• A price with a discount, or a bill with a service charge? Percentage increase and decrease are the fourth question in the same tool; the arithmetic is the same whether the number is going up or down.
• How much longer is this text than the limit? Use the word and character counter in the text category, then the percentage calculator to express it as a share of the limit.
• How many working days until the deadline? That is date arithmetic rather than a percentage: the business days calculator counts them, with your own holidays.

Other tools and guides on this site

These calculators do arithmetic on numbers you supply. When the question turns out to be about dates or about money over time, these are the pages that continue it.

• Date and time — the gap between two dates, working days, and Unix timestamps.
• Business days calculator — when the percentage is really a deadline.
• Job offer comparison calculator — percentages and totals across two offers, including bonuses and equity.
• All tools — every calculator and utility on the site, grouped by what it is for.
• Editorial policy — how these pages are written, and what we refuse to state without a citable source.

Common questions

Are these calculators free, and is there a usage limit?

Free and unlimited. The arithmetic happens in your browser, so there is no server call to meter, no account to create and no daily cap. Close the tab and the numbers you typed are gone; open it again and you start from an empty form rather than someone else's half-finished calculation.

Why is there no tax rate, interest rate or tip percentage built in?

Because those are local, they change, and they need a source we could cite. A tax rate that looks authoritative and is a year out of date is worse than no rate at all, so these calculators take the numbers you already have and do the arithmetic on them. A percentage is a percentage wherever you are; the rate actually offered to you is written on your own paperwork.

Can I use these for a real money decision?

For the arithmetic, yes — that is all they do, and you can check every figure by hand or with a second calculator. What they will not do is tell you whether the answer is good: a loan at a given rate over a given term is a fact, while whether to take it depends on your income, your alternatives and the terms in the contract.

Why do two of your percentages disagree with each other?

Usually because one is a percentage change and the other is a percentage-point difference. Going from 4% to 6% is a rise of two percentage points and a rise of 50%, and both statements are true. The percentage calculator asks which of the four questions you mean rather than assuming, because mixing them up is the most common error in this category.

Do they work offline, and do they work on a phone?

Both. Each page is a static file with a local module behind it, so once it has loaded a lost connection changes nothing, and there is no app to install. The forms are ordinary inputs and the results update as you type, so a phone keyboard and a desktop keyboard behave the same way.