Half life is determined on one's body metabolism. Half life can be anywhere from 1-10 days. Let take an example of a 5 day half life. For example you have 200ng of thc in your system. After 5 days you would have 100ng of thc in your system. After another 5 days you would have 50ng of thc in your system. After another 5 days you would have 20ng of thc in your system. After another 5 days you would have 10 ng of thc in your system. After another 5 days you would have 5ng of thc in your system. After another 5 day you would have 2.5ng of thc in your system. Hope this was helpful.