We don't know is the simple answer,but the consensus of opinion says that about 14 days after exposure, although other studies show that it may be longer......much longer, although one is most contagious in the first few days after infection.
Was that you're question?
If a person is tested positive for Covid a week after contacting the disease, then that person is contagious for only 7 to 10 days.
How long a person is infectious for after contracting Covid and being diagnosed may be quite differing time spans.
Confused?
Contact and patient rules differ.