Formula to Calculate Margin

Just because I see this so often in spreadsheets:

Costs * 1.Margin = Resale

The proper way to apply a margin to your cost is:

Cost / ( 1 - Margin) = Resale

It makes a big difference on the final number:

100 * 1.3 = 130
100 / ( 1 - .3) = 142.86

If you do it the first way at some point you are going to be wondering why you are short 7%.

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