Jessica Simpson Celebrates the End of Her 30s by Getting Back Into Her 14-Year-Old Jeans

Jessica Simpson turns 40 on July 10 and celebrated one night early by fitting into a pair of jeans she bought in her 20s. On Thursday night, Simpson posted a mirror selfie in which she was modeling the jeans in question, sharing that she first bought them 14 years ago. “I have kept these throwback True Religion jeans in my closet for 14 yrs (I’m not exaggerating!),” she wrote. “I figured that since I’m in the final hours of my 30’s I’d give them another try, and hello 40, so nice to meet you.”

After giving birth to daughter Birdie in March 2019, Simpson lost 100 pounds, a milestone she celebrated in September. “6 months. 100 pounds down (Yes, I tipped the scales at 240),” she captioned two photos of herself at the time. “My first trip away from #BIRDIEMAE and emotional for many reasons, but so proud to feel like myself again. Even when it felt impossible, I chose to work harder.”

“She set a goal and she went for it,” a source told PEOPLE of Simpson’s weight loss. “She had a hard time not feeling like herself.” Along with working with a trainer and doing plenty of walking, the insider said that Simpson “really cut out junk food.”

“She ate a lot of vegetables. She also discovered the vegetables she likes that can also be masked into different dishes,” the source said. “And she limited foods that were fried and high in calories. But she did not deny herself and gave herself nice healthy meals. She believes in moderation and she was conscious of her goal. At certain times she allowed herself to indulge.”

Prior to her birthday, Simpson and husband Eric Johnson celebrated six years of marriage earlier this week and Simpson used Instagram to share a picture of the two with her gift, a crystal geode in the shape of a butterfly. “Eric Johnson, my Husband, I love you,” the designer wrote. “6yrs ago today I married my perfect soulmate. Our unity was written in God’s sky of colliding stars. Together we manifest dreams, nurture desire and hold space. Destined, it always has been and always will be, forevermore. Also, anyone who knows me at all knows that this crystal butterfly is my dream gift.”