Jessica Simpson posts cheeky bikini photo ahead of 40th birthday: 'Final days in my 30s'

Jessica Simpson is embracing the end of her 30s! The 39-year-old fashion designer took to Instagram to share a bootylicious bikini photo of herself wearing a brown and white cow skin-printed two-piece from her own collection, a black lace coverup, and a black cowboy hat with gold embellishments.

"YEE-HAW to my final days in my 30’s 😜," she captioned the shot.

The mother of three officially turns 40 on July 10. She's been hard at work staying fit amid quarantine.

Last month a source close to Simpson told ET, "She is walking outdoors and on her treadmill. It’s the way she stays sane, so it’s as much for mental health as it is for physical wellness."

And when it comes to diet, it's all about moderation for Simpson. "There has definitely been a lot of baking going on with the kids and she doesn’t totally deny herself," the source added, noting that portion control is important for the mother of three.

For more on how Simpson's staying healthy and fit following the birth of her daughter Birdie in 2019, watch the clip below: