The 36-year-old singer and designer marked the occasion Wednesday by sharing a family photo of herself with Johnson, 5-year-old daughter Maxwell and 3-year-old son Ace.
"7 years, 2 kids, and a whole lotta love later #may21 #MAXIDREW #ACEKNUTE," she captioned the picture for her 3.7 million Instagram followers.
"We got an IUD. Nothing's going to get in that uterus," she told host Ellen DeGeneres. "I have two beautiful children and I'm not having a third. They're too cute. You really can't top that."
Simpson had said in an interview with Access Hollywood in 2014 that marrying Johnson shaped her identity more even more than motherhood.
"Eric is the best. Being married, for me, it defines me so much more than even having kids," the designer said.
"[Marriage] actually has changed my style," she added. "I'm very into slip dresses and everything's a little bit sexier. I feel sexier as a wife and a mom!"
Simpson last released the holiday album Happy Christmas in 2010.