The chance of a perianal abscess turning into a fistula depends on the severity of the abscess. Generally, if left untreated, abscesses can lead to fistula formation in approximately 25-50% of cases. However, if an abscess is caught early and treated properly with antibiotics, surgical drainage, and other therapies, the chance of it developing into a fistula is much lower. Additionally, if the abscess is complicated or recurrent, the risk of it forming a fistula increases significantly.