This informal expression refers to the processing, calculation, or analyzing numerical data, especially in relation to how much money is available or needed for something. When you crunch the numbers you work out the calculation of something. Crunching the numbers often involves boring, time-consuming work that is done by a person or a computer. The term can be used in a social context, especially in relation to personal finances, and professionally with regards to sales, profits, quotas etc. Another informal phrase with a similar meaning is 'do the math,' which tends to be more commonly used in North America.