If you test positive, your self-isolation period should begin on the day your symptoms started (or the day you had the test, if you did not have symptoms).
You may need to self-isolate for longer if you get symptoms while self-isolating or your symptoms do not go away.
Read more about how long to self-isolate.
Can I mix with my household or kitchen group?
If you have symptoms you need to self-isolate and stay away from other people as much as possible.