It depends on your baby. For my children it was a waste 2 of them were able to wear newborn stuff for almost 2 weeks. My oldest was only able to wear one outfit in his hospital picture.
Also different brands are sized differently.
My son only fit into newborn for about a week lol every baby is different and like the above posted, every brand is different. I'd get some newborn clothing but just get very little for now.
I promise that buying newborn sizes are a waste of money. Just buy one or two outfits for pics at the hospital if you like but better to buy size 3 or size 0-3.
My babies wear newborn for 2-3 weeks before moving up. But both me and my husband are very small and we have small babies. Depends on how big your baby is.
I had pretty big babies (almost nine pounds each) and I had them both in newborn clothes for probably a month if not more. I really enjoyed the clothes fitting them well to show off their chubby little bodies. But that's just me, I think it looks cuter on babies when they're close fit them well, but not too tight obviously!