In this month's Glamour magazine, the 38-year-old Academy Award winner says, "It was always going to have my name. Mia and Joe have it as part of their name, so it would be weird if this baby didn't. Of course we're not going to call it Rocknroll. People might judge all they like, but I'm a f***ing grown-up."
The couple's newborn baby, Bear, joins Winslet's 13-year-old daughter and 10-year-old son from previous marriages.
On the topic of losing the baby weight, Winslet says, "Having just had a baby, I'm not going to be thinking about my arse."