The 23-year-old actress announced on her website Sunday that she and her hockey-player husband, Mike Comrie, are expecting their first child.
She wrote that she and Comrie celebrated their first wedding anniversary over the weekend, and "We also want to share the exciting news that.. BABY MAKES THREE!!!"
She said they are "extremely happy and ready to start this new chapter of our lives" and thanked her fans for their support.
Duff rose to fame as the star of the Disney Channel's "Lizzie McGuire" and recently appeared on "Gossip Girl." Comrie most recently played for the Pittsburgh Penguins.