What is the deadline to register for Self Assessment?

5 October after the end of the tax year you need to file for. For the 2025/26 tax year (ending 5 April 2026), you must register by 5 October 2026. Late registration can trigger a £100 penalty even before any tax is due. Self-employed people should register within 3 months of starting trading.

Do I need to register for Self Assessment if I just have rental income?

Yes — if your gross rental income exceeds £1,000 (the property allowance) you must register via SA1 and declare the income. Below £1,000 you can claim the property allowance and avoid the requirement. Joint owners split the income according to ownership shares.

How to register for Self Assessment 2026/27

Last reviewed by the UK Tax Drag editorial team · 12 May 2026 · How we review · Next review due 12 November 2026 · See what changed · Report an error

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How to register for Self Assessment in 2026/27?

Quick answer: To register for Self Assessment: employed/non-self-employed people use form SA1 (online or paper) ; self-employed sole traders use form CWF1 ; partners in a partnership use SA401 . After registration, HMRC sends your Unique Taxpayer Reference (UTR) within 10 working days , then a separate Government Gateway activation code within another 10…

Key points:

Self-employed (sole trader) with income over £1,000
Partner in a business partnership
Untaxed income over £2,500 (e.g. tips, rental income)

To register for Self Assessment: employed/non-self-employed people use form SA1 (online or paper); self-employed sole traders use form CWF1; partners in a partnership use SA401. After registration, HMRC sends your Unique Taxpayer Reference (UTR) within 10 working days, then a separate Government Gateway activation code within another 10 days. You must register by 5 October after the end of the tax year you need to file for (e.g. by 5 October 2026 for the 2025/26 return).

Do you need to register?

You must register for Self Assessment if any of the following applied during the tax year:

Self-employed (sole trader) with income over £1,000
Partner in a business partnership
Untaxed income over £2,500 (e.g. tips, rental income)
Total income over £150,000 (any source)
Capital gains tax to pay on disposals over the annual exempt amount
HICBC applies because adjusted net income exceeds £60,000 and you or your partner claim Child Benefit
Foreign income over £2,000
Director of a company (some cases — see HMRC guidance)
Income from trusts, settlements or estates
State Pension recipient with other income that requires tax adjustment HMRC can't make via PAYE

You don't need to registerif all your income is taxed through PAYE and you don't fall into any of the above categories. The decision tool at gov.uk/check-if-you-need-tax-return walks you through the exact checks. Most employees never need Self Assessment.

The three registration forms

Form	Who uses it	How to use
SA1	Non-self-employed (e.g. high earner, HICBC, rental income, CGT)	Online at gov.uk, OR paper form posted to HMRC
CWF1	Self-employed (sole trader)	Online at gov.uk, OR paper form posted to HMRC
SA401	Partner in a partnership (each partner registers individually)	Online at gov.uk, OR paper form posted
SA400	The partnership itself (one form per partnership, not per partner)	Paper form posted to HMRC

Most people use SA1 or CWF1. SA1 is for people who have UK tax to declare but aren't running a business. CWF1 doubles as registration for Class 2 NICs (relevant for self-employed earnings).

Step-by-step: registering via SA1 online

Step 1: Decide if you have a Government Gateway accountIf you've used HMRC online services before (Personal Tax Account, employee tax code check), you probably already have a Government Gateway account. Sign in with those credentials. If not, you'll create one as part of the registration.

Step 2: Go to the SA1 online serviceSearch "register for Self Assessment" on gov.uk OR go directly to gov.uk/register-for-self-assessment/not-self-employed. Click "Start now".

Step 3: Sign in or create the Government Gateway accountIf creating a new account: you'll need an email address, a strong password, and two-factor authentication (text message or authenticator app). Save your Government Gateway ID — you'll need it forever.

Step 4: Answer registration questionsHMRC asks: full name, address, NI number, date of birth, employer's PAYE reference (if employed), reason for registering (dropdown: dividends, rental income, foreign income, HICBC, CGT, etc.), tax year you need to file for, current contact details.

Step 5: Submit and wait for the UTRHMRC confirms registration immediately on-screen. Print or save the confirmation. Your 10-digit Unique Taxpayer Reference (UTR) arrives by post within 10 working days. The UTR is the number you use for all future Self Assessment correspondence — keep it safe.

Step 6: Wait for the activation codeHMRC sends a separate letter with a Government Gateway activation code, typically 7-10 days after the UTR letter. The code is valid for 28 days. Use it to "activate" online filing at tax.service.gov.uk.

Step-by-step: registering via CWF1 (self-employed)

CWF1 is the same process as SA1 but with an extra question about your business: trade type, business name, start date of self-employment.

Example: starting a freelance business in May 2026

Sarah starts freelancing as a graphic designer on 15 May 2026. The tax year 2026/27 runs 6 April 2026 - 5 April 2027.

Register for Self Assessment via CWF1 within 3 months of starting (no later than 5 October 2027)
UTR received late May / early June 2026
Activation code received late June / early July 2026
File first tax return online by 31 January 2028 (for tax year 2026/27)
Class 2 NICs were abolished from April 2024, but Class 4 NICs apply to profits over £12,570 at 6% (£50,270) / 2% above

Key deadlines

Event	Deadline	Penalty if missed
Register for SA	5 October after tax year end (e.g. 5 Oct 2026 for 2025/26)	£100 + interest on unpaid tax
File paper return	31 October after tax year end	£100 immediate, escalating after 3/6/12 months
File online return	31 January after tax year end	£100 immediate, escalating after 3/6/12 months
Pay any tax owed	31 January after tax year end	5% surcharge after 30 days, 10% after 6 months, 15% after 12 months + interest
Second payment on account	31 July following	Interest only (no surcharge)

The 5 October trap.Many people assume registration is part of the filing process. It isn't. You must register before you can file. The £100 penalty for late registration is separate from the £100 late-filing penalty. Both can apply to the same return.

Common mistakes

Mistake 1: Confusing registration with filing."Registering" means asking HMRC to set up a Self Assessment record for you. "Filing" means submitting the actual tax return. They are separate steps with separate deadlines (5 October vs 31 January).

Mistake 2: Losing the UTR.The UTR is your permanent Self Assessment ID. Store it digitally and in paper form. HMRC can issue a duplicate but only after security checks — often takes 4-8 weeks.

Mistake 3: Letting the activation code expire.Activation codes are valid for 28 days from issue. If you miss the window, request a new one — but each request adds 10-14 days delay.

Mistake 4: Registering when you don't need to.If your only income is taxed through PAYE and you don't trigger any of the registration reasons, registering creates a year-after-year obligation to file. You can de-register if your situation changes — write to HMRC explaining you no longer need to file.

Mistake 5: Not registering each partnership partner.Each partner must register individually (SA401), even if the partnership itself is registered (SA400). HMRC frequently penalises individual partners who haven't registered.

What you can do once registered

Registration unlocks access to the full Self Assessment online service:

File the SA100 (main tax return) and supplementary pages (SA102 employment, SA103 self-employment, SA105 property, etc.)
Pay tax via Direct Debit, bank transfer, or card
Set up a Time to Pay arrangement if you can't pay in full
View Statement of Account showing what you owe
Authorise a tax agent (HMRC form 64-8) to file on your behalf
Amend a previously-filed return (within 12 months of the filing deadline)
Claim refunds for overpaid SA tax

Get the first-timer Self Assessment guide

If this is your first return, our first-timer guide walks through what to gather, which boxes apply to your situation, and what to expect from the online filing service.

Read the first-timer SA guide →

Sources and references

SA registration guidance from gov.uk/register-for-self-assessment. Filing deadlines from gov.uk Self Assessment deadlines. Penalty regime from gov.uk Self Assessment penalties. Class 2 NICs abolition from Spring Budget 2024.

UK Tax Drag is not authorised by the Financial Conduct Authority and does not provide regulated financial or tax advice — see the content disclaimer for the full position. The methodology page documents how every guide is built and reviewed.

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