Jessica Simpson's maternal instincts are kicking in -- the singer is feeling pretty sure about her unborn baby's gender.

I think it's a girl, she told People. But I don't know yet.

Fiancé Eric Johnson disagrees.

I think it's a boy, he told People. We're pretty much at a standstill there.

They won't have to wait long, though.

Simpson and Johnson will find out their baby's gender on Monday, she told the style Web site Fashionista.com.

I find out on Monday, she told the Web site. I can't wait to go home to find out!