Should amortization be deducted from sales for the calculation of gross profit?

I want to evaluate profitability by customer. For that I'm looking at gross profit by customer. But I don't know what to do with amortization. Should I take it into account in the GP calculation or after GP?

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I'm used to the term gross margin rather than gross profit. You subtract only the cost of sales, also called direct costs, or unit costs . . . those things that go up and down with sales.

Some special industries include amortization as direct costs, like rental business--but that's rare.

And then some people talk about gross profit as gross margin less expenses. In that case, amortization, which is an expense, would count.

Tim