Excel BODMAS rule and the errors that can arise

One of the most common logic errors made in Excel is not using the BODMAS or BIDMAS rule that applies to maths and is used within Excel. A recent error we found in a clients spreadsheet related to the incorrect use of the Excel BODMAS rule.

What is BODMAS

BODMAS stands for Brackets Of Division Multiplication Addition Subtraction and tells you the order the you must prioritize the calculations. This is important to get the correct answer.

Example of BODMAS errors

So imagine we are doing movement studies and have determined that an event takes 0.2 of an hour to go the one way and 0.1 of an hour to repeat the process on the return leg. If you want to see what the total return time is in minute we need to add these 2 together and multiple the answer by 60 to convert it to minutes.

Below the answers you get depending on whether you put in the brackets into the Excel calculation or not.

0.2+0.1*60=6.2 minutes

vs

(0.2+0.1)*60=18 minutes

In the first option, because we have no brackets, the BODMAS rule multiplies the 0.1 by 60 (BODMAS) and then adds the result to the 0.2 (BODMAS). This is clearly very wrong and results in a 67% error. When you use the brackets, it correctly treats the addition portion correctly.

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