The 26-year-old has a two-and-a-half-year-old son Luca Cruz.
“One of the coolest things about being a mom is this newfound confidence in every aspect of my life,” Duff was quoted by people.com as saying.
“I was a little uncomfortable with (my body) in the beginning because it goes through a lot of changes, but now I’m more grateful than ever for what it can do for me,” she added.
She said it took her some time to lose extra weight, but now she is strong.
“I feel strong as hell and fierce! It took me a while to totally get back in shape, but I’m proud of my body,” she said.