In this invention, the detachable T-shirt collar, DTSC, is for a regular T-shirt without any provision for a detachable collar. This invented collar is attached through or close to the stretchable T-shirt collar band at the neck to transform a regular T-shirt, old or new, into a more formal attire. The collar attachment is for the standard O-neck and V-neck and the stretchable T-shirt material is compatible with the collar material. The fastening method can use various methods such as a pin, paired magnets, paired male and female clip connectors and tension clips that open and close, all of which can be made from a variety of materials such as metal or plastic.