Without Treatment Ringworm can take several months to clear up on it's own. By several months I mean that it could take up to 8 months or longer for the Ringworm to clear up on it's own and during that time the Ringworm is likely to spread to other parts of your body.
You should always treat Ringworm by either going to the doctor for antibiotic ointment or getting some over the counter ointment to treat the Ringworm.
Ringworm should always be treated to get rid of the Fungal bacteria that is causing the Ringworm.
When you treat the Ringworm the Ringworm will go away much faster and should be cleared up within 3 to 4 weeks.