The 2023-24 tax year ended on 5 April 2024 and the new 2024-25 tax year started on 6 April 2024. Most taxpayers will be happy to leave dealing with their 2023-24 self-assessment tax returns until later this year or even until January 2025.
 

The new rules will not change the accounting period of the business, however the tax position will move from a current year basis to a tax year basis. This will mean that  business profits will be calculated for the tax year rather than for the period of account ending in the tax year. 

The basis period rules for unincorporated businesses are being changed from the 6 April 2024, with a transitional year of the 2023/24 tax year.