The 49-year-old actor marked the milestone Wednesday by sharing a sweet photo with the 46-year-old actress on Instagram.
The picture shows Smith smiling as he and Jada cozy up for the camera. The actor wears a fleece jacket, while Jada sports a yellow sweater and leopard-print scarf.
"I just realized... This year we've been together more than HALF OUR LIVES! @jadapinkettsmith," Smith captioned the post.
Smith and Jada married in December 1997, and are parents to 20-year-old son Jaden and 17-year-old daughter Willow. Smith explained in an interview in July why he and Jada no longer refer to themselves as married.
"We refer to ourselves as life partners, where you get into that space where you realize you are literally with somebody for the rest of your life," the star said on Tidal's Rap Radar podcast.
"There's no deal breakers. There's nothing she could do ever. Nothing that would break our relationship," he added. "She has my support till death and it feels so good to get to that space."
Jada posted a sultry bikini photo the same month during her family vacation with Smith and their children. Smith is also parent to 25-year-old son Trey with ex-wife Sheree Zampino.