Once a day, occasionally twice. I'll often not change if I'm not going anywhere (pretty much the summer). Basically, I change after I dance in the mirror and sing in the shower
I change it everyday, but one time I couldn't change it for four months, it's a really bad and long story don't judge, it was a life risk trust me, I could've got infected with a life threatening disease it was a horrible time, luckily Beyonce dropped her album on the day I got new underwear