do the math

verb2

1. •
   (US) To perform a mathematical calculation.

   • 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. — 2002
2. •
   (US) To determine the explanation for or precise nature of a situation, such as the motive underlying someone's behavior, based on available facts.