Form CWF1 is the HMRC form you use to register as self-employed when you start working for yourself as a sole trader. Sending it in tells HMRC to set up your Self Assessment record and start your National Insurance contributions as a self-employed person. Most people now register online through GOV.UK, but the paper CWF1 is still available if the online route doesn’t suit you.
Who Should Use CWF1
CWF1 is for individuals registering a trade: sole traders starting out, and people already in Self Assessment for another reason (rental income, for instance, or higher earnings) who now need self-employment added to their record.1ICAEW. How to Register Clients for Self Assessment or as Self-Employed
It isn’t the right form for every situation. If you need to file a Self Assessment return but aren’t trading — say you only need to declare untaxed investment income — that’s the SA1 form. Business partnerships use different forms and processes again.2HM Revenue & Customs. Self Assessment Manual – Records: Set Up Taxpayer Record: Notification of New Business or Self Employment
When You Have to Register
You must tell HMRC about your self-employment by 5 October after the end of the tax year you started trading in. If you began any time between 6 April 2025 and 5 April 2026, your deadline is 5 October 2026.3GOV.UK. Self Assessment Tax Returns: Deadlines
Register late and HMRC will send you a letter or email with a revised deadline for your first return, typically three months from the date of that letter. The payment date doesn’t move: any tax you owe for the year is still due by 31 January following the tax year, whether you registered on time or not.3GOV.UK. Self Assessment Tax Returns: Deadlines
Registering Online or on Paper
The Online Route
The fastest way is GOV.UK’s “Register as a sole trader” service, which asks a short set of questions and submits your details to HMRC electronically.4GOV.UK. Register as a Sole Trader Online submissions are processed automatically in most cases, with no manual handling at HMRC’s end.2HM Revenue & Customs. Self Assessment Manual – Records: Set Up Taxpayer Record: Notification of New Business or Self Employment
The Paper Form
If you’d rather use paper, or can’t use the online service, download CWF1 from GOV.UK. An interactive version lets you type your answers on screen before printing, which keeps everything legible and avoids delays from handwriting HMRC can’t read. Sign the printed form and post it to:
Self Assessment
HM Revenue and Customs
BX9 1AN
United Kingdom
What to Have Ready
Gather these before you start filling anything in:
- Your National Insurance number, from a payslip, tax code letter, or previous HMRC correspondence.
- Your Unique Taxpayer Reference (UTR) if you already have one. It’s a 10-digit number on previous tax returns or in your HMRC online account. First-time registrants don’t have one yet; HMRC issues it once your form is processed.5GOV.UK. Find Your UTR Number
- The exact date you started trading. HMRC uses this to work out which tax year your first return covers.
- Your business name (if it differs from your own) and the address you work from, including a home address if that’s where you operate.
- A short description of what you do, such as “graphic design” or “plumbing services.” HMRC uses this to assign a trade classification.
Filling Out the Form
The form opens with your personal details: full name, date of birth, current address, National Insurance number, and UTR if you have one. This section links your new self-employment to your existing identity in HMRC’s systems.
Next comes business information: the date you started (or plan to start) trading, the nature of your business, and the address you operate from. Be specific about your trade. Vague descriptions can slow processing because HMRC may come back for clarification.
A final section asks about any previous self-employment. If you traded before and stopped, this bridges the gap in your record. Check every entry against your official documents before you send it. Inaccurate information can lead to penalties, and fixing a record after the fact takes time.
What Happens Next
HMRC will write to confirm your registration and, if you didn’t have one already, send your Unique Taxpayer Reference. Allow at least a few weeks for the letter to arrive. Once your UTR is in hand, you can set up your HMRC online account to manage Self Assessment, file returns, and pay electronically.
From then on, HMRC expects a Self Assessment return each year: 31 October for paper, 31 January for online. Your first return runs from your business start date to the following 5 April.
Penalties for Registering Late
Miss the 5 October deadline and fail to pay all your tax by 31 January, and you can face a “failure to notify” penalty. It’s a percentage of the unpaid tax, not a flat fee.6GOV.UK. Self Assessment Tax Returns: Penalties
The rate depends on your behaviour and whether you came forward on your own or HMRC prompted you:
- Non-deliberate, unprompted, within 12 months: 0% to 30% of the tax owed.
- Non-deliberate, prompted or more than 12 months late: 10% to 30%.
- Deliberate, unprompted: 20% to 70%.
- Deliberate, prompted: 35% to 70%.
- Deliberate and concealed, unprompted: 30% to 100%.
- Deliberate and concealed, prompted: 50% to 100%.
HMRC won’t charge a penalty if you had a reasonable excuse, the failure wasn’t deliberate, and you told them without unreasonable delay once the excuse ended.7HM Revenue & Customs. Compliance Checks – Penalties for Failure to Notify – CC/FS11 The practical point: register as soon as you start trading, and if you realise you’ve missed the window, contact HMRC yourself rather than waiting. Unprompted disclosure almost always brings a lower penalty.
National Insurance After You Register
Registering also brings you into the National Insurance system as a self-employed person. Two classes matter for sole traders.
Class 2
If your profits are £6,845 or more a year, Class 2 contributions are treated as paid automatically, protecting your NI record. Nothing to pay separately. If your profits fall below £6,845, you can pay voluntary Class 2 at £3.50 a week to keep your entitlement to the State Pension and certain benefits.8GOV.UK. Self-Employed National Insurance Rates
Class 4
Class 4 is the main NI charge on self-employed profits. For 2025–26, you pay 6% on profits between £12,570 and £50,270, and 2% on anything above £50,270.9GOV.UK. Rates and Allowances: National Insurance Contributions It’s collected through Self Assessment alongside your income tax, so there’s no separate payment to arrange.