At birth, I'm not sure. Probably a couple weeks, but you will end up making a lot that gets wasted until you figure out roughly how much your LO wants most feeds (even then it will always be changing). So you may go through it more quickly, but probably because you'll throw a lot away. At the point when my daughter was having the most, probably between 5 and 8 months, we went through 1 a week, maybe every 5-6 days if she was really taking a lot.