# Using percent key on calculator **URL:** \ **Category:** Factual Questions\ **Created:** [March 27, 2012, 3:29am UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923 "2012-03-27T03:29:46Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![srzss05](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@srzss05](https://boards.straightdope.com/u/srzss05)\ **Post date:** [March 27, 2012, 1:53pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/21 "2012-03-27T13:53:54Z")
> [@srzss05](#): > > That works for 100, but what would you do for, say, 8.25% of 67? > I just enter 67+67\*.0825, and get the correct results. I never found a calculator that used the percentage key the same way each time, and never bothered to use it when it had one. Too late to edit, but I just realized I had a brain fart. Even so, the last part is relevant. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [March 27, 2012, 1:56pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/22 "2012-03-27T13:56:24Z")
> [@Dervorin](#): > > It’s also consistent with the behaviour of the multiplication, since 100 \* 0.1 = 10. I think this is the key: it’s _only_ consistent with the multiplication (and division I guess). That’s purely what it’s designed for. That it fails to work how one would expect addition of a % to work would probably have been irrelevant to the original programmers - because I bet the calc app was just ported over from an old calculator. ---
**Author:** ![Dervorin](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Dervorin](https://boards.straightdope.com/u/Dervorin)\ **Post date:** [March 27, 2012, 3:16pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/23 "2012-03-27T15:16:06Z")
> [@jjimm](#): > > I think this is the key: it’s _only_ consistent with the multiplication (and division I guess). That’s purely what it’s designed for. That it fails to work how one would expect addition of a % to work would probably have been irrelevant to the original programmers - because I bet the calc app was just ported over from an old calculator. As \*\*jragon \*\*noted above, it’s how programmers think. Clearly programmers are strange and curious folk. I should know; I am one. Normal people, however, are less likely to want their calculators to behave like this, and more likely to want them to give the increase in percentage based on the original value (i.e. 100 + 10% = 110). I think all desk calculators behave this way, as do all the Casio scientific calculators that I’ve owned. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [March 27, 2012, 3:42pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/24 "2012-03-27T15:42:44Z")
> [@Mr.Greenjeans](#): > > Not really. > > I typically wouldn’t use the % key at all for this calculation. To add 8.25% to 100, I would enter: > > 100 \* 1.0825 This is almost exactly what I was going to say. ---
**Author:** ![spanna](https://avatars.discourse-cdn.com/v4/letter/s/a6a055/32.png) [@spanna](https://boards.straightdope.com/u/spanna)\ **Post date:** [March 27, 2012, 3:46pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/25 "2012-03-27T15:46:16Z")
> [@Dervorin](#): > > As \*\*jragon \*\*noted above, it’s how programmers think. Clearly programmers are strange and curious folk. I should know; I am one. > > Normal people, however, are less likely to want their calculators to behave like this, and more likely to want them to give the increase in percentage based on the original value (i.e. 100 + 10% = 110). I think all desk calculators behave this way, as do all the Casio scientific calculators that I’ve owned. My calculator is a Casio fx-991MS ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [March 27, 2012, 4:09pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/26 "2012-03-27T16:09:55Z")
This is simple: to add 8.25% tax to a sum, enter **sum X 1.0825 = \_\_\_\_** Works every time. ahh- beaten to it- ---
**Author:** ![Dervorin](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Dervorin](https://boards.straightdope.com/u/Dervorin)\ **Post date:** [March 27, 2012, 4:43pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/27 "2012-03-27T16:43:45Z")
> [@spanna](#): > > My calculator is a Casio fx-991MS Interesting. I should go home and check, in case my memory is playing me false. Windows calculator gives me 110, and the scientific mode doesn’t have a % button. Apparently in scientific mode you’re too cool to need a % button. ---
**Author:** ![Heracles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/heracles/32/487_2.png) [@Heracles](https://boards.straightdope.com/u/Heracles)\ **Post date:** [March 27, 2012, 5:03pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/28 "2012-03-27T17:03:05Z")
> [@Dr.Strangelove](#): > > It sounds like an odd way to implement a percent function, but I’ll point out that (100% - 8.25%) of 108.99 is almost exactly 100. It is as if instead of multiplying by 1.0825, it is dividing by 0.9175. Same goes for your other example: 50\*1.06 = 53, while 50/0.94=53.19. Go to [this page at CalculateNow.biz](http://www.calculatenow.biz/business/markup.html) and enter : Selling price : 108.99 Cost price : 100 Click Calculate and you will get : Gross Profit (%) : 8.25 % ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [March 27, 2012, 5:58pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/29 "2012-03-27T17:58:06Z")
> [@Heracles](#): > > Click Calculate and you will get : > > Gross Profit (%) : 8.25 % I guess it makes sense if the calculator has some kind of switch to select markup vs. gross profit mode, though that still seems odd to me. I’m having a hard time imagining a situation where you know the original number and not the final, and want to work with gross profits. I can see having original+markup and wanting the final price, or having the final price+gross profit and wanting to calculate the original number, but other combinations sound less useful. Anyway, as others say, just avoid the percent key and use straight decimals. No ambiguity. ---
**Author:** ![Kimballkid](https://avatars.discourse-cdn.com/v4/letter/k/b5a626/32.png) [@Kimballkid](https://boards.straightdope.com/u/Kimballkid)\ **Post date:** [March 27, 2012, 6:09pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/30 "2012-03-27T18:09:58Z")
I’ve never done it the way **awottokat** does it. The way I did it on my ancient Casio calculator was: 100 \* 8.25% + = and got the correct result. When I did it as 100+8.25%, I got the same result as he/she did. ---
**Author:** ![cochrane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cochrane/32/10441_2.png) [@cochrane](https://boards.straightdope.com/u/cochrane)\ **Post date:** [March 27, 2012, 6:21pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/31 "2012-03-27T18:21:50Z")
I guess from the responses, people’s calculators can function differently from each other, but I tried using the % on two different calculators, one I bought in the 80s, and the other built into my iPhone and got identical results. Taking 8.25% of 100, and adding it to 100, I entered # 100 + 8.25 % key 8.25 (shows on display) 108.25 Taking 8.25% of 67 and adding it to 67, I entered # 67 + 8.25 % key 5.53 (shows on display) 72.53 Both calculators gave the same correct answers in each case. So, although not all calculators treat percentages in the way **awottokat** was looking for in the OP, at least a few do. I guess it’s best not to depend on it for consistency, but better to just use a decimal all the time since different models of calculators can vary widely in some of their functions. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [March 27, 2012, 9:17pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/32 "2012-03-27T21:17:53Z")
This is why I never use the % button on a calculator. I already know what I want, so I just calculate it. To use the % button, I’d have to figure out how it works. Then remember it for the next time. Then hope the next calculator I use works the same way. ---
**Author:** ![hogarth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hogarth/32/1773_2.png) [@hogarth](https://boards.straightdope.com/u/hogarth)\ **Post date:** [March 28, 2012, 3:39pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/33 "2012-03-28T15:39:23Z")
> [@jjimm](#): > > On my Android calculator app, 100 + 10% = 100.1 > > WTF. Not exactly intuitive. Huh. I thought all calculator % keys did this. I always thought it was pretty useless as a kid, but it’s what I’m used to. ---
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [May 2, 2012, 7:57am UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/34 "2012-05-02T07:57:47Z")
> [@Dervorin](#): > > As \*\*jragon \*\*noted above, it’s how programmers think. Clearly programmers are strange and curious folk. I should know; I am one. > > Normal people, however, are less likely to want their calculators to behave like this, and more likely to want them to give the increase in percentage based on the original value (i.e. 100 + 10% = 110). I think all desk calculators behave this way, as do all the Casio scientific calculators that I’ve owned. I know this thread is old, but let me explain **why** I think this way. The percent symbol has a meaning, there’s a difference between 10% of x (as in “10% of my 20ml of alcohol is Vodka”) and 10% off x (as in “this fabulous blouse was 10% off its normal $20 price at Macy’s”). Former: 10% \* x Latter: x - (10% \* x) Now, you might say, “but x - 10% \* x” is intuitive, it’s what I think of when I say x - 10%!" Well, yes, but now you’re defining the percent key to have completely different meanings depending on context. That’s not something you usually want in a calculator. Even as a non-programmer, I want my calculator keys to be as unambiguous as possible, I want to know that the -\>Frac button will turn a rational decimal into a simplified fraction every time. I don’t want to have to guess on a test, or while doing life-saving ballistics calculations, that the percent key MAYBE does this or that. Even if you still want it to be context dependent, what does it do in the case of y + 10% \* x? Sure, you can define rules (such as multiplication takes precedence by PEMDAS so it makes it operate as .1), but given there’s no standard rules for this behaviour it introduces even more guesswork. This leaves only one real option – 10% = .1; which does make it a rather useless button, but it’s the only uniform option that really makes sense to me. Like I said above, I can see a reasonable need/desire for a button such as x + 10%OF which is a macro for x + 10%\*x, but I think making the default percent key assume that makes the user do too much guessing. Granted, according to this thread making it NOT do that is already making the user do too much guessing. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 2, 2012, 2:44pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/35 "2012-05-02T14:44:23Z")
I hate the percent key on the calculator. And I hate the percent format in Excel. I never use either. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [May 2, 2012, 4:54pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/36 "2012-05-02T16:54:17Z")
I never noticed before this thread, but my HP 12C (I think 12C; label fell off) has both a % key and a delta% key. My wife’s 11C has them too. A \ B % gives B% of A. i.e. it gives B \* A / 100 A \ B delta% gives the percentage change from A that gets you B. i.e it gives you 100 \* (B-A)/A. (For those who don’t know, HP 12C uses Reverse Polish Notation. i.e., it has an Enter button, and no = button. So to add 2 and 3, I’d press 2 \ 3 +. The result 5 would be on the display.) ---
**Author:** ![Shark\_Sandwich](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@Shark\_Sandwich](https://boards.straightdope.com/u/Shark_Sandwich)\ **Post date:** [May 2, 2012, 5:37pm UTC](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923/37 "2012-05-02T17:37:18Z")
I’ve always understood that calculators that can calculate percentages the way we’re talking here (100 - X% or 100 + X%) are called “sales calculators.” They’re designed to assist people in the sales industry to easily calculate margin, sell price, etc. [Previous page](https://boards.straightdope.com/t/using-percent-key-on-calculator/616923.md?page=1)