thc has an initial half life of about 4hrs...as low as 2, as high as 6 depending on yiur body and lifestyle, in normal healthy people ie no issues metabolizing........ and a terminal half life about 30hrs. this is due to the high logp of the drug aiding in absorption to fatty tissue. and why heavy daily users can have a hardertimecleansing
People who don't regularly smoke would be unlikely to test positive beyond 48hrs
A week for heavy smokers.
Pretty easy to calculate