It's different for everyone. This is what we did: I introduced the sippy around 6 months. I would just put water or diluted juice in it. She never drank much from it, just played around a bit. I tried to put formula in it, but it never worked. So she would get the sippy with water or juice with breakfast, lunch, and supper and the bottle as snacks between meals. (If you want to put formula in the sippy for meals, you can). Then when Leah was 11 months old I started putting cold cow’s milk in her sippy for meals. Now she gets cow’s milk for meals and water for snacks. If your bottles fall around meal time you could offer formula in the sippy and then follow up with the bottle. They will turn their noses up at the milk or formula at first, but you need to be persistent. Eventually they will understand.