It is a tool that lets you do a simple calculation: how many percent of X is Y? The tool is pretty straightforward. All you need to do is fill in two fields and the third one will be calculated for you. Other than being helpful with learning percentages and fractions, this tool is handy in many different situations. For example, you may calculate an amount of income tax. That is pretty much all you need to know. Keep reading if you would like to know a little more.
What is percent?
One percent is a hundredth. We use a % sign or pct to denote it. So 5 percent is the same as 5%, 5 pct, 0.05, 5/100 or five hundredths. It is as simple as that and percentage calculator is a tool to do it :). Read more on What is percentage.
It is all nice, but we usually do not use percents just by themselves. Sometimes we want to say how big is one number in relation to another number. For example, what is 40% of 20? It is 40 hundredths of 20, so if we divided 20 cookies into 100 even parts (good luck with that!), 40 of those parts would be our 40% of 20 cookies. Let's do the math:
40/100 * 20 = 8. A little tip is in order: to divide by 100, simply move the dot two spaces to the left. In our calculation,
40/100 * 20 could be done as
(40 * 20) / 100 (same thing).
40 * 20 is 800. Move the dot in 800 by 2 digits to the left and you get 8.00. 8! In our calculator, enter 40 and 20 (so it reads "40% of 20" is...). To learn all the tricks, read how to calculate percentage.
On another occasion we want to say that one number changed by some percents. For example, if we had 10 apples and we ate 2 of them... We lost 20%. Why? Because 8 is 80% of 10. We had all of the apples 100%. Now we just have 80%, so we lost 20% (because
100 - 80 = 20). In percentage calculator you would use the form which has the sentence "8 is 20 percent decrease from 10". Here is more: percentage increase and percentage decrease pages.
The term percent is often attributed to Latin per centum ("per hundred"). Actually it is wrong. We got the term from French pour cent. However, the whole idea of thinking in the terms of hundredths comes from ancient Greece. Please note that it is based on Wikipedia and there is a  right where we would like to see a source. So do not quote me on that!
Percent or per cent?
It depends on your diet, really. If you eat hamburgers for majority of your meals, it is percent. If you prefer fish and chips, it is per cent. If you spray your fish-smelling chips with vinegar, then it is per cent, mate (as opposed to burger eaters' percent, dude). When it comes to percentage, both sides of the pond are in agreement: it should be a single word. Still confused? Americans say percent, British use per cent. Something tells me American English is more popular nowadays, so this website uses a single-word form.
What is per mille?
Per mille, per mil, per mill or simply ‰ is similar to percent, only it is one thousandth (1/1000 or 0.001). If our household's budget is $2400 and we allocated 1 per mille of that to buying chewing gum, we would spend 2.4 dollars (2 dollars 40 cents) on annoying our teachers (well, 20 years ago it was not allowed in Polish schools... do not know the rules nowadays :-) ). if you wanted to use percentage calculator to count per mille, simply use numbers 10x lower (0.2 instead of 2, 4 instead of 40).
We use percentage points when we talk about a change between two percentages. When interest rate increases from 5% to 6% it's an increase by 1 percentage point (or by 20%).