Sorting out tax year, tax payment rate

I have a main job which pays me above the personal tax-free allowance. I have also worked in other side jobs. My main job tax and national insurance is paid by employer. However, I have some queries on the taxation for the side jobs. 1, I have difficulty in sorting out tax year for each of the jobs. In some cases, I worked from September 2023 to March 2024 but got paid later in April 2024, which changes tax year. Could you clarify in which tax year I should count the payment for tax purposes? Is it the tax year of work or the tax year as per receipt date or tax year as per actual payment date? 2. If the income from all the side jobs is less than 3500 £ in total, I do not need to pay National insurance for the side jobs. Could you confirm whether this understanding is correct?

Hi
From the information provided I am assuming your main job is in employment and so the employer has applied PAYE and deducted tax and national insurance. With the side jobs if they are on a self employed basis then please read here Cash basis for income tax income and expenses. National insurance details for self employed is here Self-employed National Insurance rates

Dear HMRC Admin, Thank you for your reply. I have more queries below and it will be helpful if you could clarify the same. 1. I understand that I can claim 1000 £ trading allowance for both tax years 2023-24 and 2024-25. Is the understanding correct? 2. If my self-employment income on "cash basis" for the tax year 2023-24 is less than 1000 £ and for the tax year 2024-25 is more than 1000 £, I need to declare the income for the tax year 2024-25 but do not need to declare or register for self-assessment for the tax year 2023-24. Is the understanding correct? Please note that, 1. This is the first time I have earned income through self-employment and filing self-assessment. I have never declared whether I am using cash basis or traditional accounting. I am following the instruction: "From 6 April 2024, cash basis will become the default method of accounting. " 2. I am using trading allowance of 1000 £.

Hi,
1. Yes, that is correct.   
2. Yes, that is also correct.
Thank you.