0-3 month formula, is that at 3 months or switch at 4 months?

bridetobe6808

I can't be the only one that wonders this right? I EB and I give LO formula on a very very rare occasion. I like to have some on back up just in case. I have SO much 0-3 months formula that was given to us at the hospital/mail, etc. LO is 3 months in a couple of days. So, would I not use the newborn formula anymore or that is ok to use up until she reaches 4 months. Hope this isn't a dumb question.