Every other day (less if his skin was drying out or breaking out) until he was 1.5 old and then every day simply because he got into way more. My week old gets a sponge bath every 2 days until his stump comes off then I will switch to every other day like the first until he's into everything. then I'll probably bathe then both together
used to be every Wednesday and Saturday night unless he got super dirty throughout the day from a blowout or something. now that he's really crawling around and moving I give him one everyday unless he doesn't look like he needs one. you don't want to bathe your baby too often especially if they're prone to dry skin