Self Assessment tax return is a form that business owners need to fill in to report how much they have earned and from what sources. The form is sent to HMRC each year. Self Assessment refers to companies given the responsibility of working out how much tax they should pay, based on their earnings. The Self Assessment tax return form is usually just called a tax return. The tax return will cover most income earned by the end of the fiscal year by January 31st and needs to be filed with HMRC if you are filing it online. If you are not filing it online, it must be with HMRC by the 31st October after the end of the fiscal year. Sometimes the sole trader’s accounting year does not match with the tax year. In this case, they will file the report on their tax earnings for the accounting year that finished during that tax year. Some income is also earned tax-free and will therefore not be reported on the tax return at all. Certain tax breaks are also handled through the tax return.