How to register for self assessment with HMRC as a new trader

Registering for Self Assessment with HMRC is a legal requirement for most new sole traders and self-employed individuals in the UK once your trading income exceeds certain levels or you have other taxable income. The process is done online through the GOV.UK website and usually takes 10-15 minutes if you have all the necessary details ready.

Completing registration promptly helps you avoid late filing penalties and ensures you receive your Unique Taxpayer Reference (UTR) in time to meet deadlines. This guide walks through the exact steps, information you will need, and mistakes that frequently cause delays or problems for early-stage founders and e-commerce sellers.

When you need to register for Self Assessment

You must register if you are newly self-employed as a sole trader and your annual trading income is above the level where you need to pay tax, or if you have other sources of income that require declaration. This applies whether you sell on e-commerce platforms, provide services, or run any kind of business as an individual.

Even if your profits are currently low, registering early can prevent rushed applications close to the 31 January filing deadline. Registration is separate from registering with Companies House; most sole traders do not need to incorporate at the start. Always check the current rules on GOV.UK because income thresholds and requirements change.

Step-by-step registration process

Go to the GOV.UK website and search for 'register for Self Assessment'.
Select the correct option for self-employed individuals or sole traders (not the company director route unless you have a limited company).
Create or sign in to a GOV.UK One Login account if you do not already have one.
Complete the online form, providing personal details, business information and National Insurance details.
Submit the application and note the reference number shown on screen.
Wait to receive your Unique Taxpayer Reference (UTR) by post, which typically arrives within 10 working days.

After receiving your UTR you can set up your personal tax account to view future deadlines and submit returns online. Keep a record of your UTR as it is needed for all future correspondence with HMRC.

Information and documents you will need

Before you begin, gather the following:

Your National Insurance number (found on your payslip, P60 or letter from the Department for Work and Pensions).
Your full name, date of birth, address and contact telephone number.
The date you started trading (use the exact date you received your first business income or made your first sale).
A description of your business activities (for e-commerce sellers this might be 'online retail of clothing' or 'sale of handmade goods via marketplaces').
Business address (this can be your home address if you do not have separate premises).
Any previous employment details from the current or previous tax year if relevant.

Having these items to hand avoids the need to save and return to the form later, which can sometimes cause session timeouts. If you run an e-commerce business, be ready to explain multiple income streams such as platform sales, own-website orders and any related services.

Common mistakes to avoid

Many new traders select the wrong registration route, such as choosing the limited company option when they are operating as a sole trader. This leads to rejection and wasted time. Double-check that you are registering as self-employed.

Another frequent error is providing an inaccurate trading start date. Using a date too early or too late can affect which tax year your income falls into. Choose the actual month and year you began receiving trading income. E-commerce sellers sometimes forget to include income from all platforms, which can create discrepancies later when cross-checking records.

Failing to keep a copy of the confirmation screen or reference number makes follow-up difficult if your UTR letter is delayed. Finally, do not ignore the postal UTR letter; you cannot file a return without it. If it does not arrive after 15 working days, contact HMRC using the details on GOV.UK rather than re-registering.

After registration: setting up for success

Once you have your UTR, create a filing routine. Record all business income and allowable expenses from day one using simple spreadsheets or accounting software. For e-commerce sellers this means tracking platform fees, advertising costs, postage, packaging and cost of goods sold.

You will usually need to file your first Self Assessment tax return by 31 January following the end of the tax year in which you started trading. Late filing incurs automatic penalties, so set calendar reminders now. Consider whether you may also need to register for VAT if your turnover is approaching the current threshold; check the latest position on GOV.UK as this changes.

Separate business and personal bank accounts where possible to simplify record keeping, even though it is not a legal requirement for sole traders. Review your records monthly rather than leaving everything until January to reduce stress and improve cash-flow visibility.

Bookkeeping and cash flow basics for new traders

Good records make Self Assessment straightforward. Keep digital copies of sales invoices, supplier receipts, bank statements and platform reports. Categorise expenses clearly: cost of sales, marketing, office costs, travel and professional fees are common headings for e-commerce businesses.

Understand the difference between turnover and profit. Turnover is total sales; profit is turnover minus allowable expenses. Only pay tax on profits. Pricing your products or services to cover costs plus a margin that leaves room for tax and reinvestment prevents cash shortages when the tax bill arrives. Review your margins regularly and adjust prices or reduce costs if needed.

Consider opening a dedicated savings account for setting aside a portion of each sale towards future tax. This simple habit avoids unpleasant surprises and improves financial control from the beginning.

Support available for new UK founders

Many free or low-cost resources exist to help with HMRC admin and basic finance. GOV.UK provides detailed guides and online tools for Self Assessment. Local enterprise partnerships and business mentoring organisations can also offer practical advice. Loomworks in West Yorkshire provides selected early-stage founders with free desks, a registered address and operator mentoring with no fees or equity taken.

Take time to understand corporation tax principles even if you are not yet incorporated, as this knowledge helps when deciding whether to remain as a sole trader or form a limited company later. Focus on building strong habits around record keeping and regular financial reviews to support sustainable growth.

Frequently asked questions

Do I need to register for Self Assessment if my business made very little money this year?

You must register if your gross trading income exceeds the current threshold that requires a tax return, even if profits are low after expenses. If in doubt, register anyway to avoid penalties. Check the latest income levels on GOV.UK because thresholds change each year.

How long does it take to receive my UTR after registering?

HMRC usually sends the Unique Taxpayer Reference by post within 10 to 15 working days. You cannot file your tax return until you have this number. Keep the registration confirmation and contact HMRC via the online help if the letter does not arrive after three weeks.

Can I register for Self Assessment before I have made any sales?

Yes. If you know you will be trading in the current tax year it is sensible to register as soon as you start business activities. This gives you your UTR in good time and lets you begin keeping proper records from day one.

What is the difference between registering as self-employed and registering a limited company?

Self Assessment registration is for sole traders and individuals with additional income. A limited company requires separate Corporation Tax registration and different filing obligations. Most early-stage e-commerce founders begin as sole traders and review their structure later.

Do I need an accountant to register for Self Assessment?

No. The online registration process is designed for individuals to complete themselves. Many new traders handle their first return without an accountant, although professional help can be useful if your affairs become more complicated with significant international sales or multiple income sources.

How to register for Self Assessment with HMRC as a new trader