When completing the short Self-Employment pages you need to complete the dates for the accounting period if you want to enter that the turnover is below £85k. HMRC calculate the profits over a 12 month period so if it is a short period they will calculate the amount over 12 months and the short pages can only be used if the turnover at that stage is still less than the allowable limit. Otherwise you would have to complete and file online the full Self-Employment pages.