But the folks at Salary.com take time every year to figure out how much the actual work is worth.
This year, they say the work of a stay-at-home mom would command an annual salary of more than $138,000. That's up about 3 percent from last year, but not as much of an increase as employers predict for their workers: 3.9 percent.
For working mothers, the amount is put at more than $85,000 this year. That is on top of any money earned in the workplace.
Much of the theoretical salary, by the way, is figured on overtime.
"Mom works multiple jobs and rarely gets a break from the action, working an average of 52 hours of overtime," said Bill Coleman, senior vice president and chief compensation officer at Salary.com, in a press release.
According to the Salary.com survey, stay-at-home moms work a 92-hour workweek while working mothers logged 49 hours, or nine hours more than their formal workweek.
By the way, Mother's Day is May 13 this year.