Wiktionary
do the math
vb. (context idiomatic US English) To do the calculation for oneself.
Wikipedia
Do the Math
For the game show with the pricing game "Do the Math", see List of The Price is Right pricing games
"Do the Math" is a song recorded by Canadian country music artist George Fox. It was released in 1998 as the second single from his sixth studio album, Survivor. It peaked at number 17 on the RPM Country Tracks chart in September 1998.
Usage examples of "do the math".
They could do the math equally well, and the casualties appalled them.