A: Rolling over is your baby's first big milestone on the road to getting mobile, and it usually happens around 4 months, but a little later or earlier is totally normal. At first your baby will only roll from his belly to back; this is easier because he can use his arms to help him take off. Back-to-belly rolling comes later, usually by 5 to 6 months, or a month after he learned to roll over initially. Your baby's first roll-over usually occurs during a tummy-time session. When placed flat on his belly, your baby instinctively uses his arms to raise his head and shoulders off the floor. This move helps him strengthen the muscles he needs to flip.