When it comes to kids, three is the magic number... for stress.Mothers of three children stress more than moms of one or two, while mothers of four or more children actually report lower stress levels, according to an exclusive TODAYMoms.com survey of more than 7,000 U.S. mothers released Monday. Call it the Duggar effect: Once you get a certain critical mass of kids, life seems to get a bit easier.

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On a scale of 1-10, with 10 being the most stressed, the average mom in our survey puts herself at 8.5. What’s stressing moms out? Plenty, from money worries to balancing the demands of work and home to feeling like her husband is sometimes just another big kid demanding attention. But the big secret of mom stress is that a lot of it comes from within: 75 percent of mothers said they stress more about the pressure they put on themselves to be “perfect” than they do the pressure or judgment they get from other moms.

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More stress nuggets from the online survey of 7,164 U.S. mothers, conducted the week of April 17 by TODAY.com and Insight Express:

  • 46 percent of moms say their husbands/partners cause them more stress than their kids do.
  • 72 percent of moms stress about how stressed they are.
  • Biggest cause of stress: 60 percent say it’s lack of time to do everything that needs to get done.
  • 60 percent of moms say raising girls is more stressful than raising boys.
  • Nine out of 10 moms stress about staying fit and attractive.