The couple, who got engaged earlier this year, have decided to hold off their union until after the 'Friends With Benefits' star gives birth to their first child in October, reported Contactmusic.
"They're not planning to get married before the baby is born," a source said.
The couple, who are reportedly expecting a baby girl, recently invested in a new USD 10 million child-friendly mansion situated in Beverly Hills, which come up with plenty of privacy, after Ashton Kutcher, 36, put his bachelor pad on the market for USD 12 million.
"They have a lot going on right now. They've been focused on prepping for the baby and the new house. But they are really happy and in love. They can't wait for their baby to arrive," the source added.
The duo were originally planning to get married in a registry office in Los Angeles so that Mila Kunis could focus on her pregnancy.
Kutcher began dating the 32-year-old brunette beauty in 2012, post his split from his first wife Demi Moore, but they have known each other since Kunis was 14.