Why this calculator exists

Almost every calculator on the internet is built for someone who already knows which calculation they need. This one is built for someone who does not.

Who this is for

Some people were taught maths badly. Some were taught it in a language they were still learning. Some were ill for the term when percentages were covered and never caught up. Some are simply out of practice, because it has been twenty years and there has been a phone in their pocket the whole time.

None of that means a person is stupid, and all of it means the usual calculator is the wrong tool. A grid of buttons assumes you know which buttons to press. A field labelledbase value assumes you know what a base value is. If you were confident about the maths, you would not be looking it up in the first place.

So this site starts from the other end. You do not choose a formula. You choose the question you already have in your head — how much tip should I leave, what will I pay in the sale, what percent did I get — and we ask you a couple of ordinary questions and show you the answer.

How everything here is written

There are a few rules we hold ourselves to, and they are the whole product:

• Every calculator is named after your question, not the technique. Not "percentage increase" but "how much did it go up or down". Not "weighted mean" but "what is my final grade".
• Every field asks something in words. If a label needs a definition, the label is wrong.
• Every answer is explained underneath in an ordinary sentence. You should be able to see how we got there and judge whether it sounds right, instead of trusting a number from a machine.
• No jargon and no clever writing. This site is read all over the world, and a great deal of that reading is done in a second or third language. Idioms, jokes and figures of speech are the first things to break in translation, so they are left out.
• There is no equals button. The answer appears while you type, and changing a number changes the answer. Nothing is submitted and nothing can be got wrong.
• We say so when we cannot help. If a target grade is no longer reachable, or a discount is impossible, the site says that plainly instead of showing a confident, meaningless number.

How we try to keep the answers right

A calculator that is friendly and wrong is worse than no calculator at all. Every calculator here has been checked against arithmetic worked out independently of the code, including deliberately awkward cases: very large numbers, zero, a bill split between nobody, a discount of more than the whole price, scores entered as fractions, and text that is not a number at all. Where an input has no sensible answer, the aim is a plain explanation rather than a crash or a silent wrong result.

That said, this is a free tool made by people, and people make mistakes. Please do not rely on it alone for anything that really matters — a tax return, a loan, a medical dose, an official grade. Check important numbers a second way. If you ever see an answer here that looks wrong,tell us and we will look at it properly.

What happens to your numbers

Nothing. The calculations run inside your own browser, on your own device. What you type is never sent to us, because there is nowhere for it to be sent — there is no account, no login and no database of your sums. When you close the page, the numbers are gone.

Your browser does remember a couple of settings so you do not have to choose them twice, such as whether you prefer the light or dark appearance and which grading scale your school uses. Those stay on your device and say nothing about who you are.

We do count visits, so we can tell which calculators are actually helping people and which need rewriting. That is ordinary page counting and it cannot see anything you type. Theprivacy policy sets all of this out in full, including how to switch the counting off if you would rather not be included.

How this is paid for

The site is free and always will be. There is no paid version, no premium tier and nothing to unlock.

Running it costs money, so the plan is to show a small number of advertisements on some pages. If and when that happens, the advertisements will be clearly labelled as advertisements, they will never be dressed up to look like part of a calculator, and they will not be placed where they can be tapped by accident. We would rather earn less than confuse the person we built this for.

Who makes this

Online Simple Calculator is a small independent project rather than a company — one person, working on it in their own time, with a lot of care given to the wording. The illustrations are byStoryset.

Because it is small, feedback genuinely changes things. Several calculators on this site exist because somebody said they could not find a simple one anywhere, and a good number of the labels have been rewritten because a reader said they did not understand them. If something here confuses you, that is useful information and it is our fault rather than yours — write tohello@onlinesimplecalculator.com or use thecontact page.

Where to start

If you are not sure what you need, the home page lists everything in three groups — money, school and everyday — and each one is described in a single line. Thecommon questions page explains percentages, tips and grades from the very beginning, assuming nothing.