 For full-time working mothers with children under 18, they earned a median salary of roughly $55,000 last year, while full-time working fathers with children under 18 earned roughly $72,000. And that's a gap that translates to loss of roughly $1,400 a month for mothers annually. This is $17,000. And if that pay gap didn't improve over the next 30 years, it could add up to over $500,000 in lost wages for mothers.