How do I calculate the percentage in cells Example 250 + 5% = 262.5

Simple arithmetic? 250 x 1.05 = 262.5

An explanation in addition to what @robleyd posted: You may read 1.05 as (100% + 5%).
“250 + 5%” Is gravely misleading. What you mean is “250 + 5% of 250”, and that’s “105% of 250”.
Now 105% is simply applied as a factor of 1.05

for those not familiar with 5% == 0,05: ‘=250*(1+5%)’ works too
(i’d hate my math teacher for not pointing this out, other pupil failed the test and turned away from math)
hello @Lupp … sleepless? you posted while i was editing …

I’m considering if your math teacher would be interested in my answer posted to this question: How to calculate percentage with 2 decimal value and percentage sign?

From long experience with many software packages, I avoid using functions that include units (%, $, etc). My advice is to do the arithmetic from first principles, properly, and if you need to be reminded of the units (%, $, etc) then put them in text in the heading of the column. It makes life easier.

A remark: Listing the percent character together with designators for units is, at least, doubtable. I would even call it wrong.
You may see it as analogous to some old numerical measures like the dozen (sometimes abbreviated as dz), but there is the fundamental difference, that it -at least in a spreadsheet- actually changes the value dividing it by 100. If you enter 5 into a cell and format the cell to an US currency format, you may get shown 5.00$, but the value of the cell will still simply be 5. If you enter 5 again, and format the cell to “percentage”, you will get 500%, and if you entered 5%, the value will be 0.05.
This is different from the usage of units. The % sign is treated as a postfix operator.
?? Of course spreadsheets respect the bad traditions of teaching about “percentages”, and manage to top them: If you enter 5% a second time into the same cell as before, you get the text “5%%” - and with 0.05, you get 0.05%. I call it the “OptimalMessPrinciple” (OMP).

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The comments left to your original query are not really answering the question [which is also my question]; from what I can gather, the % formatting in LibreOffice Calc is just a visual formatting [in my opinion, a misleading one since it provides an unexpected result] and it’s unusable.

Developers and tech people my justify the current Calc behavior as much as they like and however they want, the fact is that, for an average end-user who possibly doesn’t even bother visiting help/community pages such as this one, the current behavior is most certainly ‘not working as expected’ (in other words ‘wrong’, ‘broken’ etc.); this may also contribute to losing interest in using LibreOffice Calc and/or losing trust in using LibreOffice altogether.

There are intrinsic behaviors associated to the ability of formatting a cell as percentage that end-users are accustomed to; deviating from the ‘norm’ for the sake of winning an argument it’s just not helpful and probably harmful to the credibility of otherwise a decent and valuable tool.

If I understand correctly, what can be taken from this conversation thus far is “the percentage formatting is available but you shouldn’t be using it! And even if you did use it, it doesn’t work as you would expect…” :grimacing:

… which further boils down to “everyone who use it happily are wrong, and only my point of view is correct”.

Percent is “one hundredth”. And 1% in Calc is exactly that: 1%=0,01. There are so many uses of “percent” in the world. There is some very narrow use case for calculators, where the range of operations is very limited (and they use % amount as a multiplier for a preceding summand) - but Calc can’t use that, because its formulas are infinitely more rich.

What would be your idea what should be the result of:

  • =20+30+10% - should it use 10% of 30 or of 50? If you use summation rules, it’s left to right; but if you use multiplication, it is like you multiply 30 by 1.1 - so it should be the other way.
  • =50%+10% - should it sum the two percentages, or add 10% of 50% - the difference would be 60% vs 55%

… and so on.
People who don’t need the great flexibility of spreadsheets are better served by calculators. People who need more powerful tools need to learn how to use the power. Please avoid the “you all don’t know what you are talking about” mindset.