CIS Monthly Returns: What Contractors Must Submit

What Is a CIS Monthly Return?

A CIS monthly return is a report that contractors must submit to HMRC every month, detailing all payments made to subcontractors during that period. The return shows how much each subcontractor was paid, how much was deducted for CIS, and the cost of any materials.

Even if you did not pay any subcontractors during the month, you must still submit a nil return. Missing a return — even a nil one — triggers automatic penalties.

Who Must File CIS Monthly Returns?

You must file monthly CIS returns if you are registered as a contractor under CIS. This includes:

• Construction companies and sole traders who pay subcontractors
• Deemed contractors (businesses spending more than £3 million on construction operations)
• Government bodies and local authorities commissioning construction work
• Property developers who engage subcontractors

When Are Returns Due?

CIS monthly returns must be submitted to HMRC by the 19th of the month following the tax month. CIS tax months run from the 6th of one month to the 5th of the next.

For example:

• Payments made between 6 March and 5 April 2026 → return due by 19 April 2026
• Payments made between 6 April and 5 May 2026 → return due by 19 May 2026

The deductions themselves must be paid to HMRC by:

• 19th of the following month for postal payments
• 22nd of the following month for electronic payments

What Information Goes on the Return?

For each subcontractor paid during the month, you must include:

• The subcontractor's name and UTR
• The verification number from HMRC
• The total payment amount (gross)
• The cost of materials included in the payment
• The CIS deduction amount
• Whether the subcontractor has Gross Payment Status

You must also make a declaration confirming that you have considered the employment status of each subcontractor — that is, you have confirmed they are genuinely self-employed rather than employees.

The Employment Status Declaration

This is an important part of the return. By submitting it, you are declaring that your subcontractors are not employees in disguise. If HMRC later determines that a subcontractor should have been treated as an employee, you could face penalties and backdated PAYE and NI charges.

If you are unsure about someone's employment status, use HMRC's Check Employment Status for Tax (CEST) tool before engaging them.

How to Submit

Online via HMRC

Most contractors submit returns through HMRC's online CIS service. You log in with your Government Gateway credentials, enter the payment details, and submit. The system provides confirmation once the return is accepted.

Through Accounting Software

Many accounting and payroll software packages can file CIS returns directly to HMRC. This is more efficient if you have multiple subcontractors, as you can enter the data once and submit electronically.

Through an Agent

Your accountant or tax agent can submit CIS returns on your behalf if they are registered as your agent with HMRC.

Nil Returns

If you did not pay any subcontractors during a CIS month, you must still submit a nil return. This tells HMRC that you have not forgotten — you simply had no payments to report.

Failing to submit a nil return attracts the same penalties as a late standard return. Many contractors get caught out by this, particularly during quiet months when they assume they do not need to do anything.

You can submit nil returns online in a few minutes. Some software allows you to set up automatic nil returns for months when no payments are made.

Penalties for Late Filing

CIS late filing penalties are automatic and escalate over time:

| Period Late | Penalty | |-------------|---------| | 1 day late | £100 | | 2 months late | Additional £200 | | 6 months late | Additional £300 or 5% of deductions due (whichever is greater) | | 12 months late | Additional £300 or 5% of deductions due (whichever is greater), or up to 100% of deductions in serious cases |

These penalties apply per return. If you miss multiple months, the penalties stack up rapidly. A contractor who misses three consecutive returns could face £300 in penalties before any additional charges.

Correcting Mistakes

If you realise you have made an error on a submitted return, you should correct it as soon as possible. You can amend CIS returns through HMRC's online service or by contacting the CIS helpline.

Common errors include:

• Incorrect deduction amounts
• Wrong UTR for a subcontractor
• Forgetting to include a subcontractor
• Applying the wrong deduction rate

Correcting promptly reduces the risk of penalties and keeps your records aligned with HMRC's.

How Accounted Simplifies Monthly Returns

If you are a contractor, Accounted tracks your subcontractor payments and generates the data you need for your monthly CIS returns:

• Payment tracking — every subcontractor payment is recorded with labour and materials split
• Deduction calculation — the correct deduction is calculated based on the subcontractor's verified rate
• Deadline reminders — Penny reminds you before the 19th so you never miss a filing
• Record keeping — all CIS data is stored and ready for HMRC enquiries

View our pricing page to see how Accounted fits your contracting business.

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Never miss a CIS return deadline again. Sign up for Accounted and let Penny keep your contractor obligations on track.