Quick Answer:Â To register for Self Assessment, visit GOV.UK and complete either the CWF1 form (sole traders and self-employed) or the SA1 form (all other cases). You will receive your Unique Taxpayer Reference (UTR) by post within 10 working days. The registration deadline for the 2025/26 tax year is 5 October 2026.
Every year, millions of people across the UK need to register for Self Assessment with HMRC. Whether you have started working for yourself, taken on a rental property, begun drawing dividends as a company director, or crossed a new income threshold — registering on time is the first step to staying compliant and avoiding HMRC penalties.
This guide covers everything you need to know: who must register, which form to use, a step-by-step walkthrough of the process, and the key deadlines for the 2025/26 tax year. If you are registering for the first time, you are in the right place.
What Is Self Assessment?
Self Assessment is HMRC’s system for collecting Income Tax and National Insurance from people whose tax cannot be collected automatically through PAYE (Pay As You Earn). Unlike employees, whose tax is deducted at source by their employer, self-employed individuals, landlords, company directors, and those with complex financial affairs must calculate and declare their own tax liability each year.
You do this by completing a Self Assessment tax return — a summary of your income, allowable expenses, and any tax reliefs for the relevant tax year. HMRC then calculates what you owe (or what you are owed as a refund).
The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. If any of the circumstances below applied to you during that period, you are likely required to register.
Who Needs to Register for Self Assessment?
HMRC requires you to register for Self Assessment if any of the following applied to you during the 2025/26 tax year:
Self-Employed Sole Traders and Freelancers
You must register if you earned more than £1,000 from self-employment in the tax year — even if this was a side project alongside your regular employment. This threshold is known as the trading allowance. Crossing it means HMRC requires you to declare your business income and pay the correct National Insurance contributions.
Landlords and Property Investors
If you received rental income from a UK or overseas property, you are required to register for Self Assessment. This applies regardless of whether you made a profit — HMRC needs a record of your property income and allowable expenses. Note that the Rent a Room Relief scheme (currently £7,500 per year) may reduce or eliminate your tax liability, but registration is still required once your gross rental income exceeds £1,000.
Company Directors
Most company directors must complete a Self Assessment tax return, even if the company paid no salary or is dormant. Directors typically receive income in a combination of salary and dividends. Dividends are not taxed through PAYE, which is why Self Assessment is required to account for them correctly.
Employees with Additional Untaxed Income
If you are employed but also receive untaxed income — such as savings interest above your Personal Savings Allowance, foreign income, or casual freelance earnings — you may need to register. Similarly, if you or your partner received Child Benefit and either of you earned over £60,000 during 2024/25, the High Income Child Benefit Charge applies and requires a Self Assessment return.
Individuals with Income Over £100,000
If your total income from employment exceeded £100,000 in 2025/26, HMRC requires you to complete a Self Assessment return. This is because the Personal Allowance tapers away above this threshold and additional tax may be owed that cannot be collected through PAYE alone.
Those with Capital Gains to Declare
If you sold assets — including property, shares, or cryptoassets — and your gains exceeded the annual Capital Gains Tax allowance (£3,000 for 2025/26), you must declare them via Self Assessment.
Partners in a Business Partnership
Each partner in a trading partnership must register individually for Self Assessment. Partnership income and loss allocations are declared separately by each partner, in addition to any other personal income.
Not sure if you need to register? HMRC offers a free online tool at GOV.UK that guides you through a short series of questions to determine whether you need to file a Self Assessment return. If you are still uncertain, The Digital Accountants can assess your circumstances and advise you within the same working day.
Key Deadlines for Self Assessment Registration 2026
Missing the registration deadline can trigger penalties even if you later file and pay on time. Here are the critical dates for the 2025/26 tax year:
- 5 October 2026 — Registration deadline. If you first needed to file a Self Assessment return for the 2025/26 tax year, you must register by this date. This deadline applies to sole traders, landlords, directors, and all other new registrants.
- 31 October 2026 — Paper return filing deadline for 2025/26.
- 30 December 2026 — Online return deadline if you want HMRC to collect tax owed (under £3,000) through your PAYE code the following year.
- 31 January 2027 — Online filing deadline and payment deadline for the 2025/26 tax return. This is also the deadline for your first payment on account for 2026/27.
- 31 July 2027 — Second payment on account for 2026/27.
Registration is a separate process from filing. You must register first to receive your Unique Taxpayer Reference (UTR) before you can complete and submit your return.
Important:Â HMRC issues UTR numbers by post, and this can take up to 10 working days — sometimes longer during peak months. If you register close to the 5 October deadline, allow sufficient time for your UTR to arrive and your Government Gateway account to be activated before the January filing window.
How to Register for Self Assessment: Step-by-Step
The registration process depends on your circumstances. Follow the steps below that apply to you.
Step 1: Set Up a Government Gateway Account
All HMRC online services run through the Government Gateway. If you have never used HMRC’s online services before, you will need to create an account first. Go to the HMRC sign-in page at gov.uk/log-in-register-hmrc-online-services and select ‘Create sign in details’. You will need to verify your identity using a valid UK passport, driving licence, or HMRC correspondence.
If you have previously filed a tax return online, your existing Government Gateway credentials will work. Do not create a second account.
Step 2: Choose the Correct Registration Form
HMRC uses different registration routes depending on why you need to file. Use the table below to identify which applies to you:
- CWF1 form — Use this if you are self-employed as a sole trader or a self-employed partner in a partnership. This form also registers you for Class 2 National Insurance contributions.
- SA1 form — Use this for all other cases: company directors, landlords, employees with additional income, high earners, and those with capital gains to declare.
- SA400 and SA401 forms — Use these to register a business partnership (SA400) and each individual partner (SA401).
Both the CWF1 and SA1 can be completed online through HMRC’s website. Paper versions are available but will add time to the process.
Step 3: Complete Your Registration
During registration, you will be asked to provide the following:
- Your full name, date of birth, and National Insurance number
- Your address and contact details
- The date you started your self-employment, began receiving rental income, or first required a Self Assessment return
- The nature of your business or income source
Take care to enter your start date accurately. HMRC uses this to determine which tax year your first return covers and to set your payment schedule.
Step 4: Receive Your Unique Taxpayer Reference (UTR)
After submitting your registration, HMRC will send your 10-digit Unique Taxpayer Reference (UTR) by post to the address you provided. This typically arrives within 10 working days, though delays can occur during busy periods such as January and October.
Your UTR is unique to you and is used in all correspondence with HMRC. Keep it safe — you will need it every year to file your return, and it does not change.
Note: UTR numbers are not sent by email for security reasons. If you believe yours has been lost or not received, you can check the HMRC app or your online account, where it may be visible sooner than the paper letter arrives.
Step 5: Activate Your Online Self Assessment Account
Once you have received your UTR, HMRC will send a second letter containing an activation code for your online account. You must enter this code into your Government Gateway account within 28 days. If it expires before you use it, you will need to request a new one from HMRC — which adds further time to your setup.
After activation, you will be able to access your Self Assessment account, view previous returns, and submit your tax return online.
Step 6: Gather Your Records and Prepare to File
Registration is only the first step. Once your account is active, you will need to begin collecting the information required to complete your return: income records, receipts, bank statements, invoices, and any PAYE information from employed work. Strong record-keeping throughout the year makes the filing process significantly faster and reduces the risk of errors.
Professional tip:Â The Digital Accountants can handle your entire Self Assessment registration on your behalf — including completing the correct HMRC form, managing correspondence, and ensuring your account is fully set up and ready to file. Contact us to take this off your plate entirely.
What Happens After You Register?
Once you are registered, HMRC will expect you to file a Self Assessment tax return every year unless you formally request to stop. This applies even in years where your income falls below the filing threshold — HMRC will continue issuing you a ‘Notice to File’ until you notify them that the obligation no longer applies.
If you stop being self-employed, sell your rental property, or otherwise cease to have a Self Assessment obligation, you must inform HMRC and request to be removed from the Self Assessment register. Failing to do so will result in continued penalty notices for unfiled returns.
Your Annual Self Assessment Obligations
Once registered, your ongoing responsibilities include:
- Maintaining accurate records of all income and allowable expenses throughout the tax year
- Completing and submitting your tax return by the relevant deadline (31 January for online filing)
- Paying your tax bill and any payments on account by the relevant deadlines
- Notifying HMRC of any changes to your circumstances, such as ceasing self-employment or starting a new income source
Payments on Account
If your Self Assessment tax bill for a given year exceeds £1,000 and less than 80% of your tax was collected at source through PAYE, HMRC will require you to make payments on account. These are advance payments toward your next year’s tax bill, split into two instalments: one on 31 January and one on 31 July.
For first-time filers, this can come as a surprise — your January payment may cover both your current year’s bill and 50% of the following year’s estimated liability. Understanding this from the outset helps you plan your cash flow accordingly.
What About Making Tax Digital for Income Tax?
If you are a sole trader or landlord with qualifying gross income above £50,000 from self-employment or property, you are now required to use Making Tax Digital for Income Tax (MTD ITSA) from 6 April 2026. This replaces the traditional annual Self Assessment return with a system of quarterly digital updates submitted through MTD-compatible software.
The threshold reduces to £30,000 from April 2027 and is expected to fall further to £20,000 from April 2028, bringing more sole traders and landlords into the regime over time.
Registering for Self Assessment remains the starting point. MTD ITSA does not remove the need to register — it changes how you report income once you are in the system. If your income crosses the MTD threshold, you will also need to register separately for MTD ITSA through your Government Gateway account and connect MTD-compatible software before your first quarterly period begins.
For a full explanation of how MTD ITSA works, what software you need, and how to sign up, read our dedicated guide: Making Tax Digital for Income Tax: The Complete UK Guide (2026).
Penalties for Late Registration
HMRC takes late registration seriously. If you fail to register by the 5 October deadline, you may be liable for a failure-to-notify penalty. The size of the penalty depends on whether HMRC considers the failure to be deliberate, concealed, or the result of a simple oversight.
At minimum, a late registration that leads to a late filing will trigger the standard £100 automatic penalty the moment the return becomes overdue. This increases significantly after 3 months, 6 months, and 12 months of continued non-filing:
- After 3 months: Daily penalties of £10 per day, up to a maximum of £900.
- After 6 months: An additional 5% of the tax due or £300, whichever is greater.
- After 12 months: A further 5% of the tax due or £300, whichever is greater — in certain cases, higher percentages apply.
Interest is also charged on any tax paid late, currently at the Bank of England base rate plus 2.5%.
Registering late is not automatically catastrophic — HMRC does process late registrations — but doing so compresses your timeline, increases stress, and can lead to inaccurate returns if there is insufficient time to gather the required information before the January deadline.
Common Mistakes to Avoid When Registering
These are the errors we see most frequently among first-time registrants:
- Using the wrong form. Sole traders must use CWF1, not SA1. Using the wrong form delays your registration and may leave your National Insurance record incomplete.
- Missing the start date. Entering an incorrect start date for your self-employment or rental income affects which tax year your first return covers. It can also create gaps in your National Insurance record.
- Registering too late. The UTR postal timeline means that registering in late September or early October risks receiving your UTR after the registration deadline has passed. Register as soon as your obligation arises.
- Assuming PAYE covers everything. If you have both PAYE employment and self-employment, PAYE only covers your employed income. Your self-employment profits, expenses, and National Insurance must still be declared via Self Assessment.
- Not keeping records. Self Assessment returns require detailed records of income and expenditure. Registering without setting up a record-keeping system from day one means reconstructing months of transactions under pressure in January.
- Forgetting to activate your online account. The 28-day activation window is easy to miss. If the code expires, HMRC must reissue it — adding further delay.
How The Digital Accountants Can Help
Registering for Self Assessment correctly, on time, and through the right channel is straightforward when you know what you are doing. If you are not certain — or simply do not want to manage the process yourself — The Digital Accountants handle all of this on your behalf.
As a fully digital, cloud-based accounting practice serving sole traders, contractors, landlords, and company directors across the UK, we manage everything from initial HMRC registration through to annual filing, payments on account, and ongoing tax planning. There are no paper forms on your end. You tell us your situation, we handle the rest.
Our Digital Self-Assessment Tax Return service covers the full Self Assessment lifecycle: registration, return preparation, submission, and year-round support.
If your income exceeds £50,000 and you need to comply with Making Tax Digital for Income Tax, we can also manage your MTD ITSA registration and quarterly filing so you are not navigating a new compliance regime alone.
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Speak to the team today. We offer a free initial consultation with no obligation.
Frequently Asked Questions
The registration deadline is 5 October 2026. This applies to anyone who first needed to file a Self Assessment return for the 2025/26 tax year, including new sole traders, landlords, and company directors.
A Unique Taxpayer Reference (UTR) is a 10-digit number assigned to you by HMRC when you register for Self Assessment. It is used to identify your account in all tax correspondence. You receive it by post within 10 working days of submitting your registration. It does not change from year to year.
Yes, if you have income sources outside your PAYE employment — such as rental income, freelance work, dividends, or high earnings above £100,000 — you must register for Self Assessment even though you already pay tax through your employer.
The CWF1 form is for sole traders and self-employed individuals registering for Self Assessment and Class 2 National Insurance. The SA1 form is for everyone else who needs to register: directors, landlords, high earners, those with capital gains, and individuals with untaxed income outside of employment.
Missing the 5 October registration deadline can result in a failure-to-notify penalty. The penalty is calculated as a percentage of unpaid tax, with higher amounts applying where HMRC considers the omission deliberate. Even an honest mistake can lead to an automatic £100 penalty if it results in a late return.
Yes. Both the CWF1 and SA1 registration forms can be completed online through HMRC’s Government Gateway. This is the fastest route. Paper forms are available but take longer to process and are not recommended if you are registering close to the deadline.
The online registration process itself takes approximately 20 to 30 minutes. However, the full setup process — including receiving your UTR by post and activating your online account — typically takes 2 to 3 weeks in total. Allow additional time during peak periods such as October and January.
No. Once registered, you remain in the Self Assessment system until you formally request to be removed. HMRC will issue you a Notice to File each year. If your Self Assessment obligation ceases — for example, if you stop being self-employed — you must notify HMRC to be removed from the register.
Making Tax Digital for Income Tax (MTD ITSA) is a new digital reporting system that replaced the traditional annual Self Assessment return for sole traders and landlords earning above £50,000 from April 2026. Registration for Self Assessment remains the starting point for all taxpayers. MTD ITSA is an additional layer of compliance for those above the threshold, requiring quarterly digital updates alongside the final declaration.
Yes. A registered accountant can complete and submit your Self Assessment registration with HMRC on your behalf. They will need to be formally authorised as your tax agent, which is done through the Government Gateway. The Digital Accountants handles this process as part of our onboarding for all self-assessment clients.
Related Reading
For more on managing your Self Assessment obligations once you are registered, these guides cover the next steps in detail:
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- Self Assessment Deadlines: Key Dates for 2026/27 — every deadline you need to know for the 2025/26 and 2026/27 tax years.
- First-Time Self Assessment: A Complete Beginner’s Guide — what to expect when you file your first return.
- Making Tax Digital for Income Tax: The Complete UK Guide (2026) — everything you need to know about MTD ITSA if your income exceeds £50,000.
Digital Self-Assessment Tax Return Service — let The Digital Accountants handle your registration and filing end to end.
