CIS Monthly Returns Explained: CIS300, Deadlines & Example

A CIS monthly return (form CIS300) is the return a contractor sends to HMRC listing everyone they paid under the Construction Industry Scheme that tax month, along with the deductions taken. It is filed by the contractor, not the subcontractor, and it is due by the 19th of the month following the tax month.

This guide explains what goes on a CIS monthly return, walks through a worked CIS300 example, and covers deadlines, nil returns, and penalties. If you are a subcontractor, there is a dedicated section below on how these returns produce the deductions taken from your pay and how to check they reach your HMRC record.

What Is a CIS Monthly Return?

A CIS monthly return is a single form (CIS300) that a contractor submits to HMRC every tax month. It reports every subcontractor payment made in that month and the CIS deductions withheld from those payments.

Each return covers one tax month, which runs from the 6th of one calendar month to the 5th of the next. The deadline to file is the 19th of the month following the end of that tax month.

The return does three things:

Lists each subcontractor paid and the amounts involved
Confirms the deduction taken from each payment
Includes a declaration that the workers listed are subcontractors, not employees

Who Files CIS Returns — and Who Doesn't

Contractors file CIS monthly returns. If you pay subcontractors for construction work, you register as a contractor, deduct CIS from their payments, pay that money to HMRC, and file a CIS300 each month.

Subcontractors do not file CIS monthly returns. If you are paid under CIS, the contractor deducts tax before paying you and reports it on their return. You receive a CIS payment statement showing the deduction, and you settle your final position through Self Assessment.

Some businesses are both. A firm that is paid by a main contractor and also pays its own subcontractors is a contractor for the payments it makes and a subcontractor for the payments it receives — so it files monthly returns for the former.

What a CIS Return Includes

For each subcontractor paid during the tax month, the contractor reports:

Field	What it shows
Subcontractor name	As registered with HMRC
UTR	The subcontractor's Unique Taxpayer Reference
Verification number	HMRC's reference from verifying the subcontractor
Gross amount paid	Total paid before any deduction
Cost of materials	Materials and other costs removed before CIS
Amount deducted	The CIS withheld (20% or 30% of the liable amount)

The return also carries a declaration that everyone listed is genuinely self-employed. Getting the employment status wrong can lead to separate penalties, so contractors are expected to check that a worker is a subcontractor rather than an employee. Our guide on CIS vs employment status covers where the line sits.

CIS Deduction Rates

CIS is deducted at one of three rates, set by the outcome of verifying the subcontractor with HMRC:

Subcontractor status	Deduction rate
Registered for CIS	20%
Not registered or not verified	30%
Holds gross payment status	0%

The rate applies only to the labour portion of a payment. Before applying it, the contractor removes:

VAT charged on the invoice
Materials the subcontractor paid for directly
Plant hired for the job
Consumable stores (items used up on the job)
Fuel used on the job, except fuel for travelling

Whatever is left is the amount liable to deduction. More detail on the rates sits in CIS deduction rates explained.

CIS Monthly Return Dates and Deadlines

The CIS monthly return is due by the 19th of every month, covering the tax month that ended on the 5th. Tax months run from the 6th to the 5th.

Tax month	Period covered	Return due by
Month 1	6 April – 5 May	19 May
Month 2	6 May – 5 June	19 June
Month 3	6 June – 5 July	19 July
Month 12	6 March – 5 April	19 April

So a payment made on 20 May falls in tax month 2 (6 May – 5 June) and is reported on the return due by 19 June. A payment made on 3 May falls in tax month 1 and is due by 19 May.

Worked CIS300 Example

Here is a filled-in example for a single subcontractor on a contractor's CIS300. Figures use the 2025/26 tax year.

Scenario: Meridian Build Ltd pays Sarah, a registered subcontractor, for a job that included materials she bought herself.

Line on the return	Amount
Gross amount paid	£4,000.00
Less: cost of materials	£900.00
Amount liable to deduction	£3,100.00
CIS deduction at 20%	£620.00
Net amount paid to Sarah	£3,380.00

How the arithmetic works:

Sarah invoices £4,000 for the job.
She paid £900 for materials, which is removed first: £4,000 − £900 = £3,100.
CIS applies to the £3,100 labour portion only: £3,100 × 20% = £620.
Sarah receives £4,000 − £620 = £3,380.
Meridian Build pays the £620 to HMRC and records it on the CIS300.

The Same Job at the 30% Rate

If Sarah were not registered — or the contractor could not verify her — the higher 30% rate would apply to the same liable amount:

Line on the return	20% (registered)	30% (unverified)
Amount liable to deduction	£3,100.00	£3,100.00
CIS deduction	£620.00	£930.00
Net amount paid	£3,380.00	£3,070.00

The materials figure is not part of the deduction. Only the rate on the labour changes. For a subcontractor, a wrong rate is a cash-flow difference rather than a permanent loss — the extra is still credited as advance tax and settled at Self Assessment.

A Return With Two Subcontractors

A real CIS300 usually lists several people. The contractor totals the deductions and pays the combined figure to HMRC.

Subcontractor	Gross	Materials	Liable	Rate	Deduction	Net
Sarah	£4,000	£900	£3,100	20%	£620	£3,380
James	£2,000	£0	£2,000	30%	£600	£1,400
Total					£1,220

Meridian Build reports both lines on one CIS300 and pays HMRC £1,220 for that tax month.

How to File a CIS Return

Contractors have two main options:

HMRC's CIS online service — sign in through the Government Gateway and enter each subcontractor's details and payments manually. Suitable for contractors with a small number of subcontractors.
Commercial CIS or payroll software — files returns directly to HMRC and can handle verification and larger subcontractor lists. Useful where the same subcontractors are paid every month.

Correcting or Amending a Return

If a figure is wrong after filing, the contractor amends the return. Corrections can be made through the CIS online service or the software used to file, or by contacting HMRC's CIS helpline. It is worth correcting promptly, because the reported figures feed each subcontractor's HMRC tax record.

CIS Nil Returns and Inactivity

A CIS nil return is a monthly return declaring that no subcontractors were paid in that tax month. Contractors who register for CIS are expected to account for every month, so a quiet month is not simply skipped.

There are two ways to handle a month with no payments:

File a nil return — submit the CIS300 showing zero payments.
Request inactivity — tell HMRC the business has temporarily stopped using subcontractors, which pauses the expectation to file for up to six months.

From 6 April 2026, filing nil returns became mandatory again, having been removed in 2015. This and other reforms are covered in CIS changes from April 2026.

Penalties for Late or Incorrect Returns

Missing the 19th deadline triggers an escalating penalty. The ladder is based on how late the return is:

How late	Penalty
1 day late	£100
2 months late	£200
6 months late	£300 or 5% of the CIS deductions, whichever is higher
12 months late	£300 or 5% of the CIS deductions, whichever is higher
More serious cases	Up to £3,000 or 100% of the CIS deductions, whichever is higher

The £300-or-5% charges at 6 and 12 months are added on top of the earlier fixed penalties. The higher charge at 12 months applies where information has been deliberately withheld. Incorrect returns can also attract penalties where reasonable care was not taken, so accuracy matters as much as timing.

CIS Returns for Subcontractors: How They Affect You

You do not file the CIS300, but it shapes your tax position in three ways.

The Return Creates the Deductions Taken From Your Pay

The deduction on your payment statement is the same figure the contractor puts on their monthly return. When you understand how the return is built — labour only, at 20% or 30% — you can check your statement makes sense. Our guide to CIS payment statements breaks down every line.

The Return Feeds Your HMRC Record

When HMRC processes a contractor's return, the deductions are credited to your tax account and build up across the year. At Self Assessment, HMRC already holds a record of what was deducted and compares it against what you claim. If the two don't match, your return may be queried — which is why your own statements are your evidence.

How to Confirm Deductions Reached Your Record

You can check the CIS deductions credited to you:

Sign in to your HMRC online account through the Government Gateway.
Open your Self Assessment or CIS deductions record.
Compare the totals against your own payment statements.

Look for whether every contractor appears, whether the totals match your statements, and whether any month is missing. Because a contractor files after the tax month ends, allow until after the 19th before expecting a recent month to show.

If a Contractor Gets It Wrong

If a figure is wrong — the gross, the materials, or the deduction — ask the contractor to submit a correction to HMRC. The money already deducted is still credited to you, so you recover any excess through Self Assessment even if the record lags. If a contractor will not correct a genuine error, you can contact HMRC's CIS helpline with your payment statements as evidence.

When your deductions add up to more than your final tax bill, you claim the difference back. See reclaiming overpaid CIS and claiming back CIS deductions for how refunds work.

Frequently Asked Questions

What is a CIS return?

A CIS return, or CIS monthly return (form CIS300), is the return a contractor files with HMRC each tax month. It lists the subcontractors they paid, the amounts, and the CIS deductions taken. Subcontractors do not file it.

When is the CIS monthly return due?

By the 19th of every month, covering the tax month that ended on the 5th. Tax months run from the 6th to the 5th, so payments made between 6 May and 5 June are reported on the return due by 19 June.

Do subcontractors file CIS returns?

No. Monthly returns are filed by contractors. As a subcontractor you receive a payment statement for each payment and report your income and CIS deductions through annual Self Assessment.

What is a CIS nil return?

A CIS nil return is a monthly return a contractor files to tell HMRC they paid no subcontractors in a tax month. Alternatively, a contractor can request inactivity for up to six months. From 6 April 2026, filing nil returns is mandatory again.

What's the penalty for a late CIS return?

£100 at one day late, £200 at two months, then £300 or 5% of the deductions (whichever is higher) at six and again at twelve months. Prolonged or serious cases can reach up to £3,000 or 100% of the deductions.

How is the deduction on a CIS return calculated?

CIS applies to the labour portion only. The contractor removes VAT, materials the subcontractor paid for, plant hire, consumable stores, and job fuel, then applies 20% (registered) or 30% (unverified) to what remains.

This guide is for informational purposes only and does not constitute tax, legal, or financial advice. Tax rules change frequently. Always verify current requirements on GOV.UK or consult a qualified accountant for your specific situation.

Official Sources

File your monthly returns (CIS contractors) - GOV.UK
What you must do as a CIS contractor - GOV.UK
Make deductions and pay subcontractors - GOV.UK
Verify subcontractors - GOV.UK
Construction Industry Scheme (CIS) - GOV.UK