The Horrible Bosses actress insisted that she is not expecting a baby with partner Justin Theroux, nor is she marrying the Rock Of Ages writer.
"I'm not having triplets. Not having twins. Nor am I having one baby," she told the US edition of GQ, lifting up her shirt and gesturing to her flat stomach.
"I did not elope… You heard it here. I'm not knocked up now. I recently quit smoking, and you do put on some extra pounds. It makes a difference, especially if you're not 20."
As to why the rumors about her becoming a mother have persisted, Aniston mused: "I think people maybe want me to have a kid now... I still kind of go with, if it happens, it happens. I'm calm and peaceful with whatever the plan is. It's not something where I'm going, 'I gotta have a kid!'"
Aniston added that she is being realistic about the future of her relationship with Theroux, which she admitted was full of "awkward moments".
"It's a growing, literally living thing," she said. "There's going to be growing pains, there's going to be awkward moments - your lanky phase, your pimpled phase.
"But if the road starts to diverge and one person is growing this way and the other is growing that way... Sometimes that can happen and you can stay together, and sometimes you can't."
Aniston recently described reports of a feud with Angelina Jolie, the partner of her ex-husband Brad Pitt, as "a story headline that won't go away".
Watch Jennifer Aniston in the trailer for Wanderlust below: