When to Register
You must register as self-employed with HMRC as soon as you start trading — which means as soon as you list your first product for sale on Amazon with the intention of making profit. You have until the 5th of October following the end of the tax year in which you started trading. For example, if you start selling in August 2026, you must register by 5 October 2027. However, registering promptly is recommended to avoid penalties.
How to Register
Register online through HMRC's website. You will need your National Insurance number, personal details, and a description of your business activity (e.g., "online retail" or "Amazon marketplace selling"). Registration takes about ten minutes online. You will receive a Unique Taxpayer Reference (UTR) number by post within a few weeks, which you need for filing tax returns.
What Registration Means
Once registered, you must file a Self Assessment tax return every year and pay Income Tax on your business profits plus National Insurance contributions. You also need to keep records of all business income and expenses for at least five years. The tax year runs from 6 April to 5 April, and your return is due by 31 January following the end of each tax year.
Record Keeping Requirements
Keep records of all sales (Amazon settlement reports), all expenses (receipts and invoices), bank statements, and anything else relevant to your business finances. Digital records are fine — you do not need paper copies. Organise records as you go rather than scrambling at year-end. Cloud accounting software makes this dramatically easier.
Paying Tax
You pay Income Tax and National Insurance through Self Assessment. Tax is calculated on your profit (sales minus expenses), not on your total revenue. Payment is due by 31 January following the tax year-end, with a possible second payment on account due 31 July. As your profits grow, HMRC may require payments on account — advance payments based on the previous year's tax bill.