General Math Question (1 Viewer)

[tmyers]

Within Access, I am trying to determine margins and percent markups and such. I was doing a simple calculation of profit/total sale and then converting that to a percentage. I am however getting what I feel is not the right number, but can't figure out as to why.

In my testing, I took a cost of $29.70 and applied an 8% margin to it to give me a sale of $32.30. I had a quantity of 8 which brings the total of $258.40. All of which is correct. But on my sub-form where I am giving a breakdown of all cost (shipping, add-on's etc.), my percentage is showing as 10.22%. For one item it should just be 8% correct? So I am confused as to why I am getting 10.22% in that sub-form. Maybe I am just doing the math wrong.

 

[theDBguy]

You're only getting the wrong margin on one item out of the eight?

 

[Minty]

If you are working out the margin backwards, after it's added you can't use the same formula.

Add 10 % to 100 - You get 110
If you subtract 10% from that 110 you get 99

I suspect you are possibly doing something similar.

 

[tmyers]

You're only getting the wrong margin on one item out of the eight?

No, in the test it is (8) of the same item. So in theory, since there is only one item being calculated, if I apply an 8% market up, my overall percentage should be 8%, not 10.22% correct? Regardless of quantity because it is the same item.

If you are working out the margin backwards, after it's added you can't use the same formula.

Add 10 % to 100 - You get 110
If you subtract 10% from that 110 you get 99

I suspect you are possibly doing something similar.

You are probably right. Currently I am taking the values derived from other various textboxes (that contain formulas), then once everything is added together for total sale price, I subtracted cost from sale to get profit. I then divide profit by sale to get the percentage. That is the only method I know.

 

[Minty]

You are on the right track.

Using my earlier example to get from the 110 back to 100 you need to divide by the percentage increase (or 1 + the original markup = 1.1)

110 / (110 / 100) = 100
110 / 1.1 = 100

Using 30 %

100 + 30% = 130
130 / 1.3 = 100

 

[theDBguy]

Put another way:

100 * 1.1 = 110
110 / 1.1 = 100
100 * 1.3 = 130
130 / 1.3 = 130