Depends on how much you smoke, if your a regular smoker or not, and if you are active.
I believe THC can stay in your system for up to 2 weeks. However the more water, cranberry juice, and the more you run, sweat, and be active, will decrease the time.
Also, there are body cleansers that will cleanse it from your body.
It depends on how often you consume marijuana, your weight, and other factors. The marijuana will be the last to leave your system and can take a week to 60 days.