CCCIS Comply

CIS guide

CIS Return: how to file a CIS300 monthly return

If you pay subcontractors under the Construction Industry Scheme, HMRC needs a CIS300 monthly return by the 19th of every month — even if you paid nobody. Here is exactly what goes on it, how to file it, and how to keep the records HMRC will ask for in an audit.

CIS Comply is a record-keeping tool. It does not file returns with HMRC or replace professional accountancy advice. Always verify subcontractors directly with HMRC and consult a qualified accountant.

What is a CIS monthly return?

A CIS300 is the monthly return that every UK contractor registered under the Construction Industry Scheme must file with HMRC. It reports every payment made to subcontractors in the previous tax month (6th of one month to the 5th of the next) and the CIS tax deducted from those payments.

The 19th-of-the-month deadline

Returns must reach HMRC by the 19th of every month. Miss the deadline by one day and HMRC issues an automatic £100 penalty. The penalty rises to £200 at 2 months, £300 or 5% of the tax (whichever is higher) at 6 months, and again at 12 months. Penalties stack — they are some of the most expensive HMRC fines for a small construction business.

Nil returns: still required

If you paid no subcontractors in a given tax month, you still have to tell HMRC. This is called a nil return. You can file it through HMRC's CIS Online service in under a minute, but forgetting to file it triggers the same £100 penalty as a missed return with payments on it.

What goes on a CIS300 return

For each subcontractor paid in the tax month you need:

  • Subcontractor name and Unique Tax Reference (UTR)
  • HMRC verification reference number (e.g. V1234567890A)
  • Gross amount paid
  • Cost of materials (excluded from the deduction calculation)
  • Labour element (gross minus materials)
  • Deduction rate applied: 0% (gross), 20% (registered) or 30% (unverified)
  • Amount of CIS tax deducted

You also confirm two declarations: that the employment status of every subcontractor has been considered, and that every subcontractor on the return has been verified with HMRC.

How to file a CIS return with HMRC

  1. Sign in to HMRC's CIS Online service with your Government Gateway ID.
  2. Select the relevant tax month.
  3. Add each subcontractor and their payment, materials, and deduction.
  4. Confirm the employment status and verification declarations.
  5. Submit and save the submission reference.

If you use payroll or accounting software (Xero, Sage, QuickBooks), returns can be filed directly from the software via the HMRC API.

Record-keeping: the 3-year rule

HMRC requires you to keep CIS records for at least three years after the end of the tax year they relate to. That means verifications, payment and deduction statements (PDS), monthly returns, and the underlying invoices — all retained and producible on request.

Most contractors get caught out at audit not because they didn't file, but because they can't produce the verification reference or the PDS they gave each subcontractor. A simple log that records every verification and every payment side-by-side is enough to keep you compliant.

Frequently asked questions

When is the CIS monthly return due?

Returns are due to HMRC by the 19th of every month, covering payments made to subcontractors in the previous tax month (6th to 5th). Late returns trigger an automatic £100 penalty, rising sharply if filing is delayed further.

Do I have to file a nil return?

Yes. If you are registered as a CIS contractor but made no payments to subcontractors that month, you must still tell HMRC by filing a nil return — otherwise HMRC will assume a return is outstanding and issue penalties.

What information goes on a CIS300 monthly return?

For each subcontractor paid in the month: their name, UTR, verification reference, gross amount paid, cost of materials, the labour element, the deduction rate applied (0%, 20% or 30%) and the CIS tax deducted.

How long do I need to keep CIS records?

HMRC requires contractors to keep CIS records — verifications, payment statements, monthly returns — for at least 3 years after the end of the tax year they relate to.

Can I file a CIS return without payroll software?

Yes. HMRC's free CIS Online service lets you file CIS300 returns directly. Most contractors use a record-keeping tool alongside it so the audit trail (verifications, payment statements, deductions) is kept in one place.

Get this off your plate

CIS Comply keeps an HMRC-ready audit trail of verifications, monthly returns, and subcontractor payments. Free for up to 3 subcontractors.

  • 12-point due diligence checklist
  • HMRC verification log + GPS alerts
  • Monthly return summary + nil-return tracker

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