Do the math is a fairly recently coined slang phrase that has entered the mainstream rather rapidly. Though it is unknown who first used the term do the math, we’ll look at the meaning of the idiom, when it was coined, and a few examples of its use in sentences.
Do the math means to add up facts and figures in order to come to a conclusion. Do the math might quite literally be a demand to analyze numbers in order to make a decision on whether to proceed on a project. It may also be used to encourage someone to look at the circumstances of a situation and come to a logical conclusion. The assumption implicit in the idiom do the math is that the answer is obvious, that in fact, no examination of the facts is needed. The term is often rendered as you do the math, giving the idiom a slightly caustic edge. Do the math is primarily an American English term that first appeared in the 1980s, its popularity has grown exponentially. It has now found its way into British English usage, sometimes rendered as do the math using the preferred American spelling of math, or as do the maths using the preferred British spelling of maths.
In episode three, for example, we see him interviewing with the Brooklyn District Attorney and he’s starting to sort of do the math on the differences between being a policeman and being a prosecutor: the different people, the different cultures. (The Hollywood Reporter)
“I know when we have recruitment for lateral people outside the area and even folks just starting out, we have to really do the math and make sure they will be able to afford to live here,” he said. (The San Luis Obispo Tribune)
But you do the maths: Mongolia’s 1.5 million square kilometres are shared by just 3 million people, making it the most sparsely populated country in the world. (The South China Morning Post)