[do] the math
1
to perform mathematical calculations, especially arithmetic, to find a solution or answer to a mathematical problem
- He had to do the math to calculate the area of the square.
- Doing the math is essential for balancing the budget.
- Let's do the math to determine the total cost of the groceries.
- She did the math to figure out how much she needed to save.
- She did the math to determine the percentage of increase.