do the math

• do the maths (UK)

• Audio (General Australian):

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• Audio (Mid-Atlantic US):

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do the math (third-person singular simple present does the math, present participle doing the math, simple past did the math, past participle done the math)

1. (chiefly US) To perform a mathematical calculation.
   • 2002 February 17, Amanda Hesser, “Food Diary: Local Hero”, in New York Times, retrieved 18 December 2018:

     Before my family left for Rome, I did the math. Over 11 days, with a lunch and a light dinner, each of us could taste approximately 55 dishes.

2. (chiefly US, idiomatic) To determine the explanation for or precise nature of a situation, such as the motive underlying someone's behavior, based on available facts.
   • 2003 November 16, James Poniewozik, “All The News That Fits Your Reality”, in Time, retrieved 18 December 2018:

     Gore has looked into buying cable channel News World International. Despite initial reports, Gore's camp says he and his backers intend to make the channel not a liberal mouthpiece but a "hip" news channel. […] Maybe; maybe not. (Gore has long complained about the undue influence of conservatives on talk radio and Fox News, so you do the math.)

   • 2012, Racine Lavelle, Embracing the Wolf, →ISBN, page 117:

     “The child has marks all over. I saw them when I took her to the bathroom. Ian, she is hurting this child. Now I don't know for sure what's going on here, and maybe it's none of my business. Nevertheless, even I can do the math. […] You can't let her keep this child for one more day.”

   • 2015 December 22, Mitch Smith, “Sandra Bland’s Family Calls for Criminal Charges Against Texas Trooper”, in New York Times, retrieved 18 December 2018:

     “I can’t tell you what we’re going back to consider,” said Darrell Jordan, a special prosecutor assigned to the case, who cited Texas law regarding grand jury secrecy. “But you can do the math and figure out what it is.”

• In idiomatic usage, often used in the imperative mood.
• Although US in origin, the phrase is becoming increasingly common in the UK, despite the fact that the UK abbreviation for mathematics is maths. In UK English, the idiom may also become do the maths.

• check the math
• crunch numbers