What Is a CIS Monthly Return?

A CIS monthly return is a report you submit to HMRC every month, telling them about every payment you made to subcontractors in the previous tax month. It's not optional, and it's not just for busy months — you must file it whether you paid five subcontractors or none at all.

Think of it this way: when a subcontractor works for you under CIS, you deduct tax from their labour payments on HMRC's behalf. The monthly return is how you account for those deductions. You're essentially acting as a tax collector — and HMRC expects a receipt every month.

Who needs to file?

You must file CIS monthly returns if you are registered as a CIS contractor — meaning you pay subcontractors to carry out construction work. This applies to:

• Main contractors paying subcontractors on any construction project
• Property developers and housebuilders using subcontract labour
• Businesses spending more than £1 million per year on construction (deemed contractors)
• Subcontractors who also take on their own subbies — you are both at once

The 19th Deadline — And Why It Catches Contractors Out

Every CIS monthly return covers the tax month that has just ended. HMRC's tax months run from the 6th of one month to the 5th of the next — not calendar months. Your return for that period must be submitted by the 19th.

The deadline catches contractors out for two reasons. First, the tax month doesn't align with calendar months — the 6th start date is easy to forget. Second, many contractors conflate the return deadline with the payment deadline.

What counts as a "tax month" in practice?

Let's make this concrete. If a subcontractor invoiced you on 3 May 2026 and you paid them on 10 May 2026, that payment falls in the tax month 6 May–5 June 2026. Your return for that payment is due by 19 June. Not 19 May. The filing date is determined by when you paid, not when they invoiced.

What Information Goes on the Return?

For each subcontractor you paid in the tax month, HMRC requires the following. Getting this wrong — or leaving fields incomplete — is treated the same as a missed return.

• 1
  Subcontractor's full name and UTR You need their Unique Taxpayer Reference (UTR). If a subcontractor gives you their UTR but it hasn't been verified yet, you cannot start paying them — verify first, pay second.
• 2
  Their HMRC verification number When you verify a new subcontractor, HMRC gives you a verification number. Include this on the first return where they appear. For subcontractors already in your system from a previous return, you don't need to re-verify.
• 3
  Gross amount paid (including materials) Report the total payment before any CIS deduction — including any materials element. This is the gross figure, not the net amount that reached their account.
• 4
  Cost of materials (if applicable) CIS deductions only apply to the labour element. If your subcontractor included materials on their invoice, report the materials cost separately so HMRC can see why you only deducted on part of the total.
• 5
  Amount of tax deducted This will be 0% (gross status), 20% (registered), or 30% (unregistered/unverified). The deduction applies to labour only — never to materials, VAT, or plant hire charged separately.

How to File Your CIS Monthly Return

There are two ways to file: online via HMRC's CIS Online Service, or through your payroll or accounting software if it supports CIS filing. Most contractors use the online service directly.

• 1
  Log in to HMRC's CIS Online Service Go to gov.uk and sign in with your Government Gateway credentials. You'll need to be enrolled for CIS as a contractor. If you haven't enrolled, do it now — it takes up to 24 hours to activate.
• 2
  Select the correct tax month Choose the tax month you're filing for. Double-check the dates — 6th to 5th, not calendar month. Filing in the wrong month means HMRC sees a nil return for the real month and an unexplained return for the wrong one.
• 3
  Add each subcontractor paid Enter their details: name, UTR, verification status, gross payment, materials cost (if any), and deduction amount. The system will calculate whether your deduction is consistent with their verification status.
• 4
  Confirm and submit Review the summary carefully before submitting. Once submitted, you'll get a confirmation reference. Save it — this is your proof of filing if HMRC ever disputes receipt.
• 5
  Pay the deductions to HMRC Filing the return does not automatically pay the deductions. You must separately arrange payment to HMRC using your PAYE/CIS payment reference. Deadline: 19th of the month (22nd by Faster Payments).

What if I had no payments that month?

File a nil return. Log in, select the correct tax month, confirm you made no payments, and submit. It takes two minutes. Not doing it costs you £100.

CIS Penalties: What HMRC Charges for Late or Missing Returns

CIS penalties are automatic and cumulative. They are applied per return, per month — not as a single annual charge. A contractor who stops filing for 12 months doesn't receive one large penalty; they receive 12 separate escalating penalties.

Can penalties be appealed?

Yes — but only in limited circumstances. HMRC will consider appeals where there was a "reasonable excuse": a serious illness, bereavement, a natural disaster, or demonstrable HMRC error. "I didn't know I had to file" is not considered a reasonable excuse once you're registered. Neither is cash flow difficulty or a busy period on site.

Verifying Subcontractors — Get This Wrong and It Gets Expensive

Before you pay any subcontractor for the first time under CIS, you must verify them with HMRC. This tells you what deduction rate to apply. Applying the wrong rate — even by mistake — puts you on the hook for the shortfall.

How to verify

You can verify online through HMRC's CIS service or by calling 0300 200 3210 (Monday–Friday, 8am–6pm). You'll need:

• Subcontractor's full name (or company name)
• Unique Taxpayer Reference (UTR number)
• National Insurance number (sole traders and partnerships)
• Company registration number (limited companies)

The three deduction rates — and when each applies

How long does a verification last?

A verification is ongoing — you don't need to re-verify a subcontractor each month if they're already in your CIS return history. But you must re-verify if: you haven't included them on a return in the current or previous two tax years, or HMRC instructs you to do so.

Amending a CIS Return — When You Make a Mistake

Mistakes happen. A subcontractor's UTR was entered incorrectly. You deducted on materials when you shouldn't have. You included a payment twice. HMRC allows amendments, but the process matters.

How to amend

You can correct a submitted return online via the CIS service by selecting the relevant tax month and making the change. If the error involves the deduction amount, HMRC will adjust your liability accordingly — you may owe more, or be owed a credit.

For corrections that can't be made online, call the CIS helpline: 0300 200 3210.

Under-deduction: recovering shortfalls

If you discover you deducted too little, you have two options:

• Recover the shortfall from the subcontractor's next payment (if they're still working for you)
• Pay the shortfall to HMRC yourself if recovery isn't possible

Whichever route you take, you must report the correction on an amended return. Don't try to "balance it out" across future returns informally — HMRC's systems reconcile month by month.

Over-deduction: refunding a subcontractor

If you deducted too much — say, you applied 30% when the subcontractor should have been on 20% — you have two choices. You can refund the excess directly to the subcontractor (and adjust the return), or the subcontractor can reclaim the over-deducted amount through their Self Assessment tax return. In practice, it's usually faster and less confusing to correct it directly at source.

Record-Keeping: What You Must Keep and for How Long

As a CIS contractor, HMRC can inspect your records at any time — and can go back six years for careless errors, or 20 years where deliberate evasion is suspected. Good record-keeping is not optional.

Minimum records checklist

• Copies of all subcontractor invoices (showing labour/materials split)
• Payment records — date, amount, and subcontractor for every payment
• CIS deduction amounts applied per payment
• Verification numbers and verification dates for each subcontractor
• Copies of payment and deduction statements issued to subcontractors
• CIS return confirmation references from HMRC (save these)
• Bank statements showing CIS payments to subcontractors
• Evidence of materials costs (supplier receipts) where deduction was reduced

Real-World Scenarios: What Goes Wrong — and How to Handle It