I read other reviews and read that this was a costume that would fit more on the 9 mom side. My daughter was going to be 4 1/2 months at Halloween, and I decided to get it anyway. It was a bit long but still fit good when we got it. A few weeks later on Halloween, she was almost too long for it. But she is a large baby (99% tile for height). It still looked amazing, just the antennas didn't stay up, which is why I am only rating it 4 instead of 5 stars.