Once a week on my main guitar.
 
OTOH, Tommy Bolin rarely ever changer strings unless he broke one, and his tone is among my very favorites. 
 
Ritchie Blackmore on Tommy Bolin's guitar strings:

"When I heard that Purple hired him I thought it was great. He was always so humble. I remember he would always invite me out to his house in Hollywood to see his guitar. One day I went to his place. I walked in and tried to find him, but no one was around. There was no furnishings - nothing. I stayed there for ten minutes before he finally appeared. He showed me his guitar, and the strings must have had a quarter-inch of grime on them, as though he hadn't changed them in four years. I asked him when was the last time he'd changed strings, and he said very seriously, "Gee, I don't know. Do you think I should change them?"

once a week is pretty intense, you must play quite a bit daily. I'm just building my callouses back up before I track 

Quite a bit - I could probably keep them a bit longer, and it sometimes happen that I skip a week, but usually, I like to have a fresh set installed the night before our week resumes.
 

I don't know how you guys can do it , every time I try to buy new strings 

I always end up bringing my little wad of coffee can "just in case money " and leave the store with no strings ...
thats how I got my uke, mandolin, SG, a couple of pedals and a bunch of other stuff….
my bass is currently sporting a set of strings that will soon be having its 14 th birthday  
 
Kenny

kennywtelejazz
I don't know how you guys can do it , every time I try to buy new strings 
I always end up bringing my little wad of coffee can "just in case money " and leave the store with no strings ...
thats how I got my uke, mandolin, SG, a couple of pedals and a bunch of other stuff….
my bass is currently sporting a set of strings that will soon be having its 14 th birthday  
 
Kenny

One word - Amazon. ;)
 
I avoid torturing myself by visiting music stores unless I know precisely what I want and have the funds to get just that. 

I tend to go through strings at an alarming rate. When I was younger, single, and had only a few guitars I changed them about every other week. These days I change them when I am recording or playing out, and otherwise tend to suffer quietly with dead-ish strings in-between.
 
And yes, there is nothing quite like the sound of new strings just stretched enough to stay in tune!

I'm slapping a new set on the fretless tomorrow and then I'm going to start tracking :-) Been practicing for a couple of weeks. It's not even excessive use, but oxidation? If you put new strings on an instrument and just let it sit, and don't even play it? They will go bad with time. They don't "ring" the harmonics are out? They just don't sound or play like fresh ones. Strings are like women... They should be replaced often, and for the same reasons. Does this guitar sound ****y to you?  Funny, it sounded this way almost exactly one month ago? Hummmmm....