Just because you free feed, doesn't mean that you don't monitor the amount of food your baby eats...This is what we used to do:
Miko needed 1-1 1/4 cup of his food per day. So I would put 1 1/4 cup of food in his bowl every morning, then at the end of the evening I could see how much he had eaten throughout the day. Whatever he didn't finish, I would measure to see how much he wasn't eating...I would leave it in there because many times, he liked to eat at night. In the morning, I would check again, and usually the bowl was empty. And repeat the process
