It's normal for a baby to initially roll over in one direction before the other. Rolling over requires coordination, muscle strength, and practice, and it’s easier for babies to roll from tummy to back before they have the additional strength needed to then roll from back to tummy.

It’s common for young babies around 4 months old to move halfway from back to side, but it will be many more months until they can confidently roll back to their tummy (closer to 7 months). Before they master this direction, you’ll likely find them rolling from tummy to back in the meantime.

However, it can be helpful to encourage rolling at each stage in a way that prompts them to turn on both their left and right side. Ensure you place toys during floor time on both sides so they get equal practice pushing up and turning from both directions.