BOSTON - If a stay-at-home mum could be compensated in cash rather than personal satisfaction and unconditional love, she'd earn nearly $US117,000 ($A124,000) a year.That's according to a US study released today by Salary.com, a Waltham, Massachusetts-based firm that studies workplace compensation.The eighth annual survey calculated a mum's market value by studying pay levels for 10 job titles with duties that a typical mom performs, ranging from housekeeper and day care centre teacher to van driver, psychologist and chief executive officer.This year, the annual salary for a stay-at-home mum would be $US116,805, while a working mum who also juggles an outside job would get $US68,405 for her motherly duties.One stay-at-home mum said the six-figure salary sounds a little low."I think a lot of people think we sit ... home and have a lot of fun and don't do a lot of work," said Samantha Russell, who left her job as pastry chef to raise two boys, ages 2 and 4. "But they should try cleaning their house with little kids running around and messing it up right after them."The biggest driver of a mum's theoretical salary is the amount of overtime pay she'd receive for working more than 40 hours a week. The 18,000 mums surveyed about their typical week reported working 94.4 hours - meaning they'd be spending more than half their working hours on overtime.Working mums reported an average 54.6 hour "mum work week" besides the hours they spent at paying jobs.Russell agreed her job as a stay-at-home mum is more than full-time. But she said her "job" brings intangible benefits she wouldn't enjoy in the workplace."The rewards aren't monetary, but it's a reward knowing that they're safe and happy," Russell said of her sons. "It's worth it all." AP