When to move to 4oz?

[Iammeltin]

My DD will be 3 weeks on Monday.
shes on 3oz 8 times a day.
She finishes the bottle sometimes, sometimes she does not.
When do I move her onto 4oz?
According to the box - it’s 5-6 weeks
I don't want her to be sick.

The advice I've been given before is if they finish the bottle consistently, move them up an oz. Babies spit up milk and that's fine, they stop feeding when they're done. You might find DC will sometimes feed on the extra oz, most times they won't finish but will be gradually drinking more and going longer between feeds.