How Do You Register For Self Assessment?

By Simply Accounts on Apr 23, 2026 10:00:00 AM

Starting a business or earning income outside of standard employment is a major milestone. It represents freedom and growth, but it also brings new responsibilities toward HMRC. If you've recently become your own boss, you need to know how to register for self assessment to stay compliant.

Registration tells HMRC you have untaxed income to report. Once registered, you'll file a tax return each year, reporting what you've earned and paying any tax or National Insurance due on your profits.

Who Needs To Register?

The most common reason to register is becoming self-employed. If you operate as a sole trader earning more than £1,000 in a tax year, HMRC considers you a business. This applies whether you're a full-time freelancer or running a side hustle that's gaining traction.

Business owners aren't the only ones who need to register. You also need self assessment if you receive extra income not taxed through PAYE.

Common examples include:

• Rental income from a property
• Dividend income from shares exceeding the annual allowance
• Untaxed interest or capital gains above thresholds
• Income from abroad
• Tips and commission not taxed by your employer
• Income from selling goods or services online

If your financial situation has become more complex, check whether you've hit thresholds requiring a formal return. HMRC's website has a tool to help you determine if you need to register.

Even if you're employed but have significant untaxed income on the side, you'll likely need to register. It's better to check and be certain than assume you're covered.

When Should You Register?

Timing matters for tax compliance. Inform HMRC as soon as you start trading or receiving untaxed income. The deadline to register is 5 October following the end of the tax year in which you started.

The UK tax year runs from 6 April to 5 April. If you started your business in September 2025 (during the 2025/26 tax year), you'd need to register by 5 October 2026.

Missing this deadline can lead to penalties, even if you don't actually owe any tax. HMRC charges automatic fines for late registration, starting at £100 and increasing the longer you delay.

Getting the administrative side sorted early means you can focus on running your business rather than chasing deadlines. Registration itself takes only 10-15 minutes online, so there's no reason to put it off.

How To Register Online

The registration process is straightforward. Visit the HMRC website and look for the "Register for Self Assessment" section. You'll need basic information ready:

• Your National Insurance number
• Contact details including address and phone number
• The date you started self-employment or began receiving untaxed income
• Details about your business (if applicable)—name, type, address

The online form guides you through each step. You'll answer questions about why you need to register and provide the necessary details. The process is mostly automated, and you'll receive confirmation once submitted.

If you have a business partner, you'll need to register for self assessment as a partnership, which is a slightly different process. Each partner registers individually and then you register the partnership itself.

The Role Of The UTR Number

Once HMRC processes your registration, they'll send you a Unique Taxpayer Reference (UTR). This ten-digit number identifies you within the tax system. It's vital information you'll need to keep safe.

You cannot file a tax return or manage your account online without this reference. HMRC usually sends it by post, and it can take up to 10 working days to arrive—sometimes longer during busy periods.

This is why registering early matters. Having your UTR ready well before the January filing deadline prevents last-minute panic. If you lose your UTR, you can retrieve it through your HMRC online account or by calling their helpline, but this adds unnecessary delays.

Setting Up Your Online Account

After receiving your UTR, set up your login for HMRC online services. This requires an activation code, which HMRC posts separately and can take another 7-10 days to arrive.

Once activated, you can:

• Submit tax returns digitally
• View your tax history and payment records
• See exactly how much you owe and when it's due
• Update your personal details
• Claim tax refunds

Digital filing is significantly faster than paper methods and provides immediate confirmation that your return has been received. You also get an extra three months to file—the paper deadline is 31 October, while the online deadline is 31 January.

Managing tax online gives you a clearer picture of your financial health. You can see payment deadlines and ensure you're putting enough aside to cover your bill.

Understanding Your Filing Obligations

Once registered, you must file a tax return every year by 31 January following the end of the tax year. For the 2025/26 tax year (6 April 2025 to 5 April 2026), the deadline is 31 January 2027.

You'll report all your income and allowable expenses. HMRC calculates what you owe, including:

• Income tax on profits above your personal allowance
• Class 2 National Insurance (if profits exceed £6,725)
• Class 4 National Insurance (on profits between £12,570 and £50,270)

Payment is due by 31 January, along with a "payment on account" toward next year's tax. Understanding these obligations early helps you budget properly and avoid nasty surprises.

How Simply Accounts Can Support You

Registering for tax is the first step in your business journey. At Simply Accounts, we believe numbers should be a roadmap, not a burden. We act as a partner, taking the complexity out of dealing with HMRC.

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