It mainly depends on what flourishes you do, the type of hands you have, how often you practice and the humidity of the area you live in.
Here's my situation:
I practice at least 4 hours a day, on and off, with palms that get sweaty fast, usually cuts and thumb fans at first, then the more damaging flourishes like springs, Le Paul Spreads, etc. I'd say Singapore is really humid
A deck of Tallys lasts me 3 weeks without proper care (i.e. not putting it back into the case and into the Porper clip). Never bothered to take note of how long they last under proper care, because it's really long