Yes, most premature babies need more calories per body weight than term babies. It takes a lot of energy to grow outside of the uterus, repair lung damage, fight infections, and cope with illness. Still, how long a premature baby will actually need extra calories for depends on their health, plus any medical challenges and how well they are growing.
My friend's premie baby was fed both breastmilk and formula after he was released from NICU. My friend told me that it was a formula recommended by her doctor because her baby needed the extra calories. He is 5 months now, happy and healthy as can be :)
thanks