As a rule, colds are contagious a day before you know you are sick, and for about two days after. At one week, if you are feeling progressively better, and unless you have a secondary infection, your cold should not be contagious.This answer should not be considered medical advice.... As a rule, colds are contagious a day before you know you are sick, and for about two days after. At one week, if you are feeling progressively better, and unless you have a secondary infection, your cold should not be contagious. This answer should not be considered medical advice...