It really depends... First, on how much you are
vaping, type of juice (dark sweet, and NET juices can all be coil gunkers. It's also going to depend on how hot you run your tank, and with what airflow. "Days" can be pretty meaningless when you add in all the other factors. Do you feel like you are getting unusually short life? I will say some of those coils aren't known for longevity. It would be helpful to know what type of juice you are running and at what wattage.
Anna