Form CWF1 is HMRC's form for registering as a self-employed sole trader for Self Assessment and Class 2 National Insurance. Use it only if you cannot register online. It is an on-screen form that you fill in, print, sign and post to HM Revenue and Customs, BX9 1AN. You cannot submit it electronically or save a half-finished copy. If you have not sent a tax return before, register by 5 October after the end of the tax year in which you started trading. Your Unique Taxpayer Reference (UTR) normally arrives within 15 working days.
Is CWF1 the right form?
Online registration through an HMRC business tax account is the standard route and is quicker. HMRC's own registration guidance says that CWF1 is the fallback for people who cannot register online. CWF1 is also only for individuals trading on their own. The form itself redirects other cases:
- Sole trader starting up. CWF1 (or register online);
- A new partnership. Form SA400;
- Joining a partnership as a partner. Form SA401. Only the nominated partner can register online;
- Company director needing a tax return. Form SA1;
- A partner that is not an individual. Form SA402.
A limited company is not registered this way. It is registered for corporation tax separately once it is incorporated.
Do you need to register at all?
If your gross income from self-employment is £1,000 or less in a tax year, the trading allowance may mean you do not need to register for that year. The CWF1 form itself points this out. Gross means turnover before expenses, so a side business with £1,400 of sales and £600 of costs is over the limit. Above £1,000, you must register for Self Assessment.
The form also says you cannot register yet if you are not starting within 28 days. Register when the business is about to start, not months ahead.
What the CWF1 form asks for
Have everything ready before you open the form, because you cannot save your progress. You will need:
- National Insurance number. You must have one before you can register;
- Personal details. Name, any previous surname, date of birth, home address, and any other address in the last 3 years;
- Contact details. Daytime phone number and an email address, if you have one;
- Residence. Whether you are UK resident and whether you have come to the UK from a non-EU country in the last 12 months;
- Any previous UTR. If you have been in Self Assessment before;
- Start date. The date you started working for yourself, or the date the trading allowance stopped covering your income;
- Business details. Trading name if any, the type of work, business address, and whether the business is in land and property or investment;
- Special categories. Whether you are a CIS subcontractor, share fisherman, Lloyd's underwriter, examiner or invigilator, or a minister of religion without a salary or stipend;
- Single client. Whether you will do all your work for one person or firm.
Two of those questions deserve care. If all your work will be for one client, the form warns that you may in fact be an employee. Check your employment status before assuming self-employment. And registering for CIS as a subcontractor is a separate step: ticking the CIS box on CWF1 does not register you for CIS.
How to submit CWF1 and what happens next
- Complete the form on screen. Answer every question not marked optional;
- Preview and print. If you change anything after previewing, preview again so the printed copy is up to date;
- Sign and date it. The declaration has to be signed by hand on the printed copy;
- Post it. Send it to Self Assessment, HM Revenue and Customs, BX9 1AN. Keep a copy and proof of posting;
- Wait for your UTR. It usually arrives by post within 15 working days, or 21 days if you are abroad, and sooner in the HMRC app. HMRC then tells you when to file.
Allow for the post. If you register after 5 October 2026 for the 2025/26 year, HMRC will set your filing deadline as 31 January 2027 or 3 months from the date of its letter, whichever is later. The tax is still due on 31 January 2027. Registering late can also lead to a penalty for failing to notify. If you started trading in 2025/26 and have not yet registered, the online route is the faster way to catch up.
National Insurance after you register
CWF1 registers you for Class 2 National Insurance, but most self-employed people no longer pay Class 2. These are the 2026/27 rates:
| Annual profits | What applies in 2026/27 |
|---|---|
| Under £7,105 (Small Profits Threshold) | Nothing to pay. You can choose to pay voluntary Class 2 at £3.65 a week to protect your National Insurance record |
| £7,105 or more | Class 2 treated as paid, so your record is protected at no cost |
| £12,570 to £50,270 | Class 4 at 6% |
| Over £50,270 | Class 4 at 2% on the excess |
Class 4 is collected through your Self Assessment return along with income tax, so registering correctly matters: it is what sets up your tax and NI account. The Small Profits Threshold rose from £6,845 in 2025/26.
Practical tips
- Use the online service if you can. It avoids postal delays and gives you an online account from day one;
- Record your start date accurately. It decides which tax year you first report in, and the 5 October deadline runs from it;
- Keep records from the first day. Expenses you pay before your UTR arrives are still allowable. See what you can claim as self-employed;
- Think ahead to MTD. If your gross trading and property income passes £20,000, Making Tax Digital will apply from April 2028 at the earliest. See our MTD deadline guide.
Acumon's accountants for sole traders can register you with HMRC as your agent and set up your records properly from the start. Our Self Assessment service handles the first return.