If you pay subcontractors for construction work, CIS isn’t optional admin — it’s a monthly compliance job. Done right, it keeps your records clean, your cashflow predictable, and your year-end straightforward. Done badly (or left too late), it’s one of the quickest ways to end up with HMRC headaches, rushed bookkeeping, and avoidable penalties.
This guide walks you through the practical CIS checklist your accountant will expect you to follow — the same basics we help contractors get right every month at Asmat & Co. If you want the wider overview first, start with Understanding the Importance of CIS Registration.
1) Confirm you’re set up correctly as a CIS contractor
Before you even think about deductions, your accountant will want your “foundations” correct:
- Your business structure is clear (sole trader, limited company, partnership, etc.)
- You’re registered for CIS contractor responsibilities where required
- Your HMRC details are up to date (UTR, PAYE scheme if relevant, correct legal name)
If you’re still unsure about your setup, it’s worth reading Who We Help to match your situation to the right support, or reviewing Sole Trader Accounting vs Limited Company Accountants so you don’t build a process on the wrong structure.
2) Verify every subcontractor before the first payment
This is non-negotiable. Your accountant will expect you to verify each subcontractor with HMRC before you pay them — because the verification determines the deduction rate you must apply.
You’ll typically be dealing with these deduction outcomes:
- 20% (registered subcontractor)
- 30% (not registered)
- 0% (gross payment status)
HMRC sets this after verification — you’re not choosing a rate based on “what they told you”.
What your accountant expects you to store for each subcontractor:
- Full name + trading name
- UTR
- Address and contact details
- Verification result (date + deduction status)
- Whether they’re VAT registered (if relevant)
3) Make sure invoices clearly split labour vs materials
Most CIS errors start here.
CIS deductions usually apply to the labour element of the payment. If invoices are vague (“Labour and materials – £4,500”) it becomes guesswork, and guesswork creates problems later.
Your accountant will expect invoices to show:
- Labour (separately stated)
- Materials (separately stated)
- Plant hire (if charged)
- VAT (if the subcontractor is VAT registered)
If you’re using cloud software, setting up the right categories and reports early saves you loads of grief. That’s exactly what we do with Quickbooks Accountants, especially for contractors who want a clean monthly routine without spreadsheets everywhere.
4) Keep a simple CIS payment log (monthly, not “at year-end”)
Bank statements alone aren’t enough. Your accountant needs a clear audit trail that ties each payment to:
- the subcontractor
- the invoice
- the labour value
- the deduction amount
- the net payment
A basic CIS log per month should include:
- Date paid
- Invoice number / job reference
- Gross amount
- Labour amount
- CIS deducted
- Net paid
- Any retention held back (if applicable)
This is where good bookkeeping supports everything else — and it’s why CIS almost always sits alongside your Services such as bookkeeping, VAT, payroll, and tax returns.
5) Issue CIS deduction statements to subcontractors
Your subcontractors need proof of what you deducted so they can reconcile their own tax position. Your accountant will expect you to keep copies of:
- deduction statements issued
- the period covered
- the amounts and deductions shown
- the reference used (invoice/job reference)
It’s a small task, but it prevents disputes later — especially when someone questions why they’ve been paid less than their invoice total.
6) File the monthly CIS return on time (even if it’s nil)
Your accountant will expect a consistent monthly filing habit. If you paid subcontractors that month, you file the return. If you didn’t pay anyone, you may still need a nil return depending on your circumstances.
Late returns can trigger penalties. As a real-world example, HMRC guidance explains that a return that’s even 1 day late can lead to a £100 penalty, with further penalties as lateness continues.
This is why we push contractors towards a repeatable monthly workflow on Contractors Accounting Services — you don’t want CIS living in your head as a “maybe I’ll do it next week” job.
7) Pay HMRC and save the proof (don’t just assume it’s sorted)
Filing is only half the job. Your accountant will expect you to:
- pay over the deductions to HMRC correctly
- keep confirmation of payment
- match the payment total to your monthly return totals
If anything doesn’t match, you want to catch it in the same month — not when you’re trying to do year-end accounts or fix a backlog.
8) Watch the VAT threshold and your pricing (CIS businesses hit it faster than you think)
Even if your focus is CIS, VAT often creeps up quickly for contractors because turnover moves fast when you’re busy.
Right now, the UK VAT registration threshold is £90,000 in a rolling 12-month period.
If you’re getting close, you’ll want to plan your pricing and cashflow properly — and if you’re unsure how VAT impacts what you charge, this explainer is useful: How Can Registration VAT Affect My Price.
9) Keep job records and contracts tidy (so your numbers have “proof” behind them)
If HMRC ever asks questions, they won’t just look at your totals — they’ll look for evidence that supports the story your accounts are telling.
Your accountant will expect you to keep:
- quotes and agreements (even if it’s email-based)
- job sheets / timesheets
- purchase orders and variations
- retention agreements (if used)
- subcontractor invoices that match the work
10) Keep a “ready for questions” CIS folder
This is the easiest win. Create a simple folder structure (cloud or local) so you can hand information over quickly whenever you need to.
Suggested folders:
- Subcontractor onboarding + verification
- Monthly CIS logs
- Monthly returns filed
- HMRC payment confirmations
- Deduction statements issued
- Contracts / job paperwork
If you want quick access to official links and reference points, bookmark Useful Links & Forms and keep Help & Resources handy for those “what do I do in this situation?” moments.
A simple monthly routine that keeps you compliant
If you want CIS to feel manageable, your month should look like this:
- Verify new subcontractors before first payment.
- Check invoices split labour/materials clearly.
- Update your CIS payment log as you pay.
- File the monthly return on time.
- Pay HMRC and store the receipt.
- Save everything into your CIS folder.
Do that consistently and CIS becomes routine — not a panic.
Need CIS handled properly (without it eating your evenings)?
If you want a contractor-friendly setup where CIS is kept tidy month-by-month alongside bookkeeping, VAT and returns, take a look at Small Business Accountants and Tax Return, then book a chat via Contact Us.
