Starting a Business Mid-Year: What Happens to Your Tax?

Starting your self-employed business halfway through the tax year does not mean you only have to deal with HMRC for half a year. The UK tax year runs from 6 April to 5 April, and your Self Assessment covers the income and expenses from the period you were actually trading.

For example, if you start working as a sole trader in November 2026, your first tax return will include your self-employed income and allowable expenses from November 2026 to 5 April 2027.

If your gross trading income is more than £1,000 in the tax year, you generally need to register for Self Assessment. For a first return, you must tell HMRC by 5 October after the end of the tax year — so income from 2026/27 generally needs to be registered by 5 October 2027

You then normally have until 31 January 2028 to submit your online tax return and pay the tax due for 2026/27.

Keep records from your first day of trading: track your income and allowable business expenses so you can accurately calculate your taxable profit.