[Updated] Are native calculators on both Apple macOS and iOS flawed?

Update (March 15):

Here are a few more equations that we tested, confirming the problem:

Original story:

No, I am not a mathematician, so I don’t have the technical knowledge to prove this. But yes, I have substantial proof to conclude that Apple’s calculators on both macOS and iOS work on logics that are different from what similar software from other – and equally respected – companies follow.

Giving credit where it’s due, the problem was seemingly first spotted by ex-Apple employee Ryan Jones, who then shared it on Twitter.

To put it in simple words, the problem is when the equation 100/20% is given to macOS’ Spotlight software to calculate, it produces 0.05 as the result. But if you use most other calculator software (for example, Ryan used Soulver), the answer is 500.

Expectedly, a healthy (and quite informative) discussion followed, with people in Ryan’s circle offering their view points on the matter. It’s worth mentioning that Ryan said he has the latest macOS version on their system – so it should be 10.13.3.

Interestingly, Nick Arnott then pointed out that Spotlight on their macOS 10.12.6 system gives 500 as the answer to the same equation.

We at PiunikaWeb then tried confirming this at our end, and could easily reproduce this change in calculator behavior – macOS 10.13.3 said 0.05, while 10.12.6 said 500.

Then we quickly tried calculating the same equation on latest iOS 11.2.6, and found Siri says 0.05 (the parenthesis you see in the following calculation were automatically added by Siri – we just asked “what is hundred divided by twenty percent”):

While the native calculator app says 500 (you can easily give it a try).

We then tried the same test on iOS 11.2.5 and iOS 10.3.3, and found they all also produce exactly same results (Siri says 0.05, while the native Calculator app says 500).

By this time, we were baffled, as not only calculation logic on macOS got silently changed, core iOS software have also been producing conflicting results for not sure how long.

How can there be two answers?

It’s actually simple, as it depends on how the calculating software is interpreting the equation. In this case, if you interpret 100/20% as (100/20)% – like Siri clearly shows it’s doing – you get 0.05. Else you get 500.

What software on other platforms say?

As Apple’s core math calculating tools were producing different results, we thought of trying out calculators from other companies.

Our first attempt was with Google’s own calculator that you get by default when you put in a mathematical equation in the Google search bar. Well, the answer came out to be 500.


Then we had a couple of Linux machines (CentOS and Ubuntu) at our disposal, so we did a quick test on them, and found the answer was again 500.


Finally, we turned to Windows, and tested on Microsoft Excel, only to find the answer was again 500.

Turning to experts

Well, as I said in the beginning of this story, I am no position to conclude how the equation in question should be solved. So I tried finding someone whom I can trust. Gladly, through one of my friends, I got in touch with an expert at one of the elite government research organizations, who – when presented with the equation in question – said the answer is 500. The explanation they offered is similar to the following:

% is a complex equator n excel rules should be given priority

Sadly, I couldn’t get more explanation from the source. However, one thing I can confirm is that by “excel rules” they meant the rule set on which Microsoft Excel works.

We managed to dig that out on Microsoft’s official website, and here’s a screenshot from the support document showing the order of precedence Excel follows.


Clearly, if you apply this to 100/20%, you’ll see it’s the % operator that should be resolved first (as division operator holds a lower priority). This means the answer should indeed be 500.

So is it a bug at Apple’s end?

Two core Apple software (Siri and the Calculator app) producing different results for a simple mathematical query does seem to be an issue. However, the change in behavior of Spotlight calculator from macOS Sierra to High Sierra could be intentional.

So, it’s for Apple to come forward and explain what’s the rationale behind the change and inconsistencies we’ve highlighted here. Hope that happens soon. Meanwhile, hop on the comments bandwagon and let us know your point of view on this matter.

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Dr. Aparajita Sharma

A budding entrepreneur by profession, and a psychologist by education. As a founding member of PiunikaWeb, I am nurturing this firstborn with my sharp-eyed expertise and even journalistic writing when needed.