How do I register for CIS as a builder?

If main contractors pay you and you pay subbies yourself, register for the Construction Industry Scheme (CIS) twice: as a subcontractor with your Unique Taxpayer Reference (UTR), and as a contractor before taking on your first subbie (GOV.UK, October 2026).

Registering as a subcontractor means contractors deduct 20%, not 30%. The contractor side goes through HMRC's new-employer registration, not the CIS subcontractor service.

CIS 340, HMRC's guide to the scheme, puts it simply: many businesses pay other businesses for construction work and are paid by other businesses too. When you are working as a contractor, you follow the contractor rules. When you are working as a subcontractor, you follow the subcontractor rules. A builder often does both in the same week.

Which registration you need

Homeowner work catches builders out in both directions. The homeowner deducts nothing from you. But the moment you pay a self-employed plasterer or bricklayer on that job, you are their contractor for that payment.

Steps to register as a subcontractor

1. Check you are self-employed, not an employee.
2. If you have no UTR, register as a new business for Self Assessment and choose "working as a subcontractor". GOV.UK says this registers you for Self Assessment and CIS at the same time.
3. If you have a UTR, use the online CIS registration service. You need your legal business name (and trading name if different), your UTR, your VAT number if you have one, the date you started trading and, depending on your circumstances, your National Insurance number.
4. Give every main contractor the exact name and UTR you registered with, so they can verify you at 20%.

If you cannot register online, the postal form for sole traders is CIS301. Our subcontractor registration guide covers this side in more detail.

Steps to register as a contractor

1. Check the people you pay are genuinely self-employed. GOV.UK says you may get a penalty if they should be your employees.
2. Follow HMRC's process for setting up as a new employer. GOV.UK says you cannot register more than 2 months before you start paying people.
3. Wait for HMRC's letter with your employer PAYE reference number and the details you need to run CIS.
4. Before the first payment, verify each subcontractor with HMRC, using the free HMRC CIS online service or commercial CIS software. HMRC tells you whether to deduct 20%, 30% or nothing.

Our guide to registering as a CIS contractor explains who counts as a contractor and the exceptions.

What this means for you

Once you are registered as a contractor, a monthly routine starts. GOV.UK says you must:

• work out each deduction on the subbie's invoice after taking off VAT, materials they paid for and other allowed costs such as plant hired for the job
• pay the deductions to HMRC by the 22nd (the 19th if you pay by post)
• give each subbie you deducted from a payment and deduction statement, and file your monthly return, by the 19th
• keep CIS records for at least 3 years after the end of the tax year

From 6 April 2026, CIS 340 says a mainstream contractor, which includes a builder, that has paid subcontractors before but pays none in a month must file a nil return by the 19th, unless it told HMRC at least 14 days before that month began that it would pay no one. A late monthly return costs £100 from the day after the deadline.

The two sides stay separate. As a sole trader, the CIS taken from you goes on your Self Assessment tax return and counts towards your tax bill. The CIS you take from your subbies is their tax, paid over to HMRC each month. In our reading, you cannot set one against the other.

A worked example

Gary is a self-employed builder. In one tax month a main contractor pays him for £2,000 of labour and £500 of materials he bought. Gary is registered and verified, so the contractor deducts 20% of £2,000, which is £400, and pays him £2,100.

The same month Gary builds an extension for a homeowner, who pays him in full with no CIS. On that job he pays a self-employed plasterer, who invoices £1,500 of labour and £300 of materials. HMRC's verification gives the 20% rate. Gary deducts £300, pays the plasterer £1,500, files his monthly return by the 19th of the following month and pays the £300 to HMRC by the 22nd. Gary's own £400 goes on his tax return. The £300 is the plasterer's.

Gross payment status

Builders with steady work often ask about being paid gross. As a sole trader you need at least £30,000 of construction turnover in the last 12 months, ignoring VAT and materials, a record of paying tax and National Insurance on time, construction work in the UK, and a business run through a bank account. GOV.UK says applying for gross payment status also registers you for CIS if you have not registered already. HMRC reviews it every year. The contractor registration is still needed if you pay subbies.

Making Tax Digital and CIS

Your gross CIS pay counts towards the income test for Making Tax Digital for Income Tax (MTD). If your income before costs on your 2025-26 tax return was over £30,000, MTD starts for you on 6 April 2027, unless it was over £50,000 in 2024-25: then you should already have started. Use the free MTD check to see where you stand, and the trades section for more on CIS.