It can very much depend on the size of your baby. My DD was in newborns for ages because she was 7lb 5oz when she was born. Yet my DS was only in them for just 2 boxes as he was 9lb 1oz when he was born. We went into infants which are the next size and only come up to bulk packs of 48 not boxes for about 3-4 weeks then he went to crawlers at about 3 months which is the size he's in now @ 4.5 months.

BTW I'm talking about huggies as they are the only ones I buy.

HTH