Cormier, who turned 40 on March 20, told TMZ Sports he's already surpassed his first plan for retirement and said his rematch with Miocic in Anaheim, California, could mark the end of the road.
"I always said that I was gonna fight [until I was 40]," he said. "I couldn't make that one, so if I hold true to what I was saying, then this would be the final one."
With his submission victory over Derrick Lewis in November, Cormier became the first fighter to successfully defend the UFC heavyweight and light heavyweight titles as a dual champion. He subsequently relinquished the 205-pound belt to focus his remaining time on the heavyweight division.
The Oklahoma State product secured the heavyweight title with his first-round knockout victory over Miocic last July.
Cormier told TMZ he doesn't expect such a lopsided bout this time around.
"I truly believe he's gonna be a better version of himself," he said. "... I think it'll be a much more difficult fight."
Cormier owns a 22-1 career record with one no-contest. His resume includes victories over Frank Mir, Dan Henderson, Anderson Silva and Anthony Johnson. His only loss came to Jon Jones in a January 2015 clash for the light heavyweight belt.
A spot in the UFC Hall of Fame awaits him whenever his career does come to a close.