Jessica Simpson
Simpson is certain she's having a baby girl, but NFL hubby Eric Johnson isn't so sure. Reuters

Jessica Simpson is pregnant, and the 31-year-old star and fiance Eric Johnson plan to find out the gender of their baby on Monday.

Will it be a boy, or a Jessica-look-a-like girl?

I'm so excited! Simpson told Us Weekly about learning the sex of her growing baby.

Simpson said she and Johnson are waiting for the gender determination to decide on a name for the baby.

We have a couple names picked out for (if it's a boy or a girl), but we're going to keep that private, she told Us Weekly.

She's not one of those who wants to wait until the baby is born to know whether it's a boy or a girl -- Simpson wants to know now.

I like to plan things out, Simpson said. It'll be good to know what colors to make the nursery. I'm obsessed with thinking about what it's going to look like.