BP's grow about a foot a year for the first three years - well, uhm ... that's according to the book. Let's put that away (it appears outdated), cause we know better. Ophiophilia and Morti already told you what to expect.
You should be feeding it f/t rat pinkies. At 12 inches long I suggest you feed it a girth-sized (can be slightly larger) rat pinky once a week. As your baby grows increase the size of the pinky accordingly. In about three months from now you will want to feed it rat pups once a week. In another three months you should be able to increase to rat weanlings. At that point, you've had plenty of time to read through the posts and will know exactly what comes next
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To prepare your f/t rat pinky: Put it into a plastic baggie and thaw it out in a warm water bath (NOT the microwave and NOT boiling water). It should have a temperature of between 98 and 100 degree. Once it feels like as if it's all thawed out, give it another five minutes, to make sure the brain thawed out as well (it's the last to do so). Now go and do the pinky dance (wiggle the mouse in front of the baby with tongs like as if it was alive).
The prefered way of feeding your snake would be in a feeding box to avoid accidental swallowing of bedding and to prevent it from becoming cage aggressive.
Your baby may not readily accept food as you plan on Saturday, due to being stressed out from moving in with you. Be prepared for that and don't panic! The people on this board have tricks up there sleeve to help you, if that should happen.
