We wear disposables at night and while battling thrush, and DD is almost 8 months and has been in size 4s for at least 3 weeks! She's aroind 19 lbs, not sure about hight but has always been on the tall side.
He's been in 3s from about 6 months to now at 14 months. I have a box of 3s that will probably finish up the month and then I'm going to move him to 4s. He's about 21 pounds and 29.5 inches. 3s still fit ok but I'm sick of the Russian roulette of possibly growing out of a size in the middle of a box. 4s fit ok with the tabs pulled tight.
We used them for about 6.5 months. They still fit her, but one day last month she suddenly started peeing through them like crazy so I moved her up. She has her appointment on Thursday, but she is 20 lbs at most and at least 31". Skinny and doesn't follow the box guidelines at all.
I can't imagine D will ready for 4s anytime in the near future...he barely tips the scale at 22 lbs and 32 in long.
Amazing how differently they can be built! We moved to 4s when 3s were leaking overnight and eventually just started using 4s all day instead of having different sizes around. DS is still less than 20 lbs (and 28") and the 4s (Target) fit fine. Size 3 was seeming a little snug on him to me by 18 lbs and the 4s aren't overly big or anything.
Hmmm I think only a couple of months. He's in 3's now but once when finish our 3's we will be ready for 4's. He's 20 lbs though at 7 months old. Hopefully the 4's will last a while since I have a nice stockpile of those.