Taking a note from her mother, Golden Globe winner Diane Ladd, Dern says she plans on rejecting the concept of birthdays and aging all together.
"My mother has made her age, I think, 20 years younger," Dern joked with ET's Nischelle Turner at the premiere of her new HBO series, Big Little Lies, at the Chinese Theatre in Hollywood on Tuesday. "Which means she was like 11 when she had me. So, I think I'm about 44 this year."
"My mom's like, 'I'm an actress, we don't discuss age,' so now, I'm kind of going with that," she added.
Dern also opened up about working on her new crime dramedy series alongside her Wild co-star Reese Witherspoon, who stars in and produces the series.
"I've only known Reese as my producer and [fellow] actress, both on Wild and now on this," Dern said. "So for me, it's an amazing gift."
"She's the most supportive producer, she's an amazing friend and an incredible actor," she added. "It's amazing to have all of that in one person and a beautiful gift to work with."
Big Little Lies premieres Feb. 19 at 9 p.m. ET/PT on HBO.