Common Cold Contagious Period
A person infected with a cold virus may be contagious for two to three days before any symptoms appear and remain so until he or she doesn't show any symptoms. This is a period of up to two weeks or so. The height of the "common cold contagious period" is when symptoms are at their worst -- usually around day 2 to day 4 of the cold.
Keep in mind that while it is possible to transmit the common cold or "catch a cold," a cold virus is not as contagious as other viruses such as the flu virus or RSV. If you have a cold, there are some things you can do to decrease the chances of spreading it (wash hands frequently, use a tissue when you sneeze etc). If you are trying to avoid the common cold, there are also some prevention tips you can try like using vitamin C and black elderberry supplements.