CIS Monthly Return Deadline UK Guide for Contractors

The CIS monthly return must reach HMRC by the 19th of the month following the tax month, which runs from the 6th to the 5th, giving you an effective 14-day filing window. Miss that date and HMRC can treat the return as late, even if you paid no subcontractors and owe no CIS deductions.

It usually happens on a Friday evening. You're closing the site accounts, matching subcontractor invoices to bank payments, and trying to submit the return before the 19th slips away. One missing verification record or an overlooked payment can turn a routine compliance job into a penalty problem.

The fix is simple, but it requires discipline. Treat the 5th as the month-end lock date, prepare the figures before the 19th, and never assume a quiet month means there's nothing to file. The 2026 nil-return change makes that assumption especially dangerous.

What the CIS monthly return deadline actually means for contractors

It is the evening of the 19th. Your site manager has just sent an invoice, the subcontractor ledger is unfinished, and the CIS return is still sitting in draft. That is how a routine filing becomes a late return. The deadline is a fixed control point, not a prompt to begin the work.

The CIS monthly return is the contractor's report to HMRC of payments made to subcontractors and deductions taken under the Construction Industry Scheme. It is generally filed as a CIS300. The responsibility sits with the contractor operating the scheme and making the relevant payments, rather than with the subcontractors receiving them. HMRC's formal requirements are set out in HMRC's CIS monthly return guidance.

The relevant tax month closes on the 5th, and the return must reach HMRC by the 19th of the following month. For example, payments made from 6 May to 5 June belong to the period ending 5 June, with filing due by 19 June. The exact dates matter because a return submitted after the 19th is late, even where the figures are correct and no deduction is due.

The deadline covers two separate jobs

“Doing CIS” means completing two linked but separate obligations:

• Report the activity: Submit the CIS300 return, or the required nil return.
• Pay the deductions: Send CIS tax deducted from subcontractor payments to HMRC by the applicable payment deadline.

Paying HMRC does not file the return. Filing the return does not settle the deductions. HMRC records these duties separately, so a contractor can pay the correct amount and still receive a late-filing penalty.

A quiet month also needs attention. From 6 April 2026, CIS-registered contractors must submit monthly nil returns again unless HMRC approves a six-month inactivity request. The practical detail is covered in Stewart Accounting's construction industry scheme responsibilities guide.

Set the 19th in the diary as the final submission date. Prepare the figures before it, check every subcontractor payment, and submit early. Contractors who leave the filing until the deadline invite problems from missing records, incorrect deductions or online service issues. A disciplined monthly close removes that risk.

How the 6th to 5th tax month and 19th filing day fit together

CIS tax months run across two calendar months. Each period starts on the 6th and closes on the 5th of the following month. The return for that period is due by the 19th of the month in which the period ends, based on HMRC's stated monthly structure (HMRC filing guidance).

Use the dates as a working calendar, not as a vague monthly reminder:

• Payments made from 6 June to 5 July belong to the June tax month. Prepare that return as soon as the period closes and submit it by 19 July.
• Payments made from 6 July to 5 August belong to the July tax month. Your filing target is 19 August.
• Payments made from 6 August to 5 September belong to the August tax month. The return is due by 19 September.

If the 19th falls at a weekend, check the applicable calendar and use the next working day. Bank holidays can also affect practical processing, so set your internal deadline earlier.

Build the return around the closing date

On the 5th, close the tax month and identify every subcontractor payment made since the previous 6th. Reconcile payment dates, invoices, verification details and deductions. Then prepare the CIS300 and check that the figures agree with your bookkeeping before submitting it.

The filing window after the 5th is short in practice. Late invoices, missing site records and unavailable managers can consume the time quickly. I advise clients to draft the return during the first week after closing and submit it well before the 19th, rather than relying on an evening filing session.

The calendar also matters for the 2026 nil-return rule. From 6 April 2026, a CIS-registered contractor with no relevant payments must submit a nil return unless HMRC has approved a six-month inactivity request. A contractor inactive from April can therefore face nil-return decisions for the April tax month, which closes on 5 May and is filed by 19 May. The same check applies after each subsequent tax-month close until the approved inactivity period covers it.

Do not let an inactive site create a missed filing. Mark every 5th for review, record whether payments were made, and confirm the nil-return or inactivity position before the relevant 19th deadline.

Filing the return versus paying HMRC where the dates differ

A subcontractor paid on 30 May belongs to the CIS tax month running from 6 May to 5 June. You must include that payment in the CIS300 return for the period and submit it by 19 June. The deduction is a separate liability: pay it to HMRC by the applicable payment deadline, which can differ from the filing date because of the payment method and calendar.

Treat the two actions as separate controls. Your bookkeeping record should show:

• CIS return submitted: note the submission date and confirmation.
• CIS deductions paid: note the payment date, amount and payment reference.

That distinction catches two common contractor errors. You can file the CIS300 correctly and still breach the payment requirement by waiting for cash flow to improve. You can also pay HMRC and forget to file the return. One action does not replace the other.

Keep the payment schedule visible beside the filing calendar. For the May tax month, for example, close the figures after 5 June, submit by 19 June, then confirm the separate HMRC payment date and reference. Authorise both tasks together, but check each one independently.

Late payment can bring interest consequences separate from a late return penalty. Review the consequences of late tax payments so a payment delay is not mistaken for a filing issue.

A short monthly control works well: reconcile the deductions, submit the return, make the payment, and save both confirmations.

A practical 12-month CIS deadline calendar you can copy

Build your CIS calendar around the tax month, not the calendar month. The first period runs from 6 April to 5 May, and the return deadline falls on 19 May. The next period runs from 6 May to 5 June, with the return due on 19 June.

The table below gives the reusable pattern. It pairs each tax month with the 19th filing date and leaves room for your separate payment control. Where the 19th lands on a weekend or bank holiday, check the applicable working-day treatment and submit earlier. Don't leave the decision until the deadline morning.

The 6th to 19th is the formal preparation period for each return. Set an internal draft date before the 19th, particularly where the deadline falls on a Sunday, Monday or around a bank holiday. This calendar assumes no approved six-month inactivity request is in force.

The 2026 nil return rule and six month inactivity request

A contractor can have no subcontractors on site, no payments to report and still have a CIS deadline. From 6 April 2026, an active CIS-registered contractor must submit a return for every tax month. That return is either a CIS300 reporting payments or a nil return confirming that none were made. BDO confirms that the nil-return deadline remains the 19th of the following month in its CIS facts guide. For practical filing steps, use this CIS tax return guide for subcontractors.

The calendar makes the change clear. If the tax month runs from 6 April to 5 May 2026 and an active contractor makes no subcontractor payments, the nil return is due by 19 May. No payments during 6 May to 5 June means another nil return by 19 June. A quiet month removes the payment data, not the filing obligation.

HMRC's internal guidance expects an active contractor scheme to send either a completed return or a nil return for each monthly return period. Late filing can still be penalised, even when the return reports no deductions (HMRC internal CIS guidance).

Choose the correct status

Use one of two routes:

• Active scheme: File the CIS300 for the tax month. If no subcontractors were paid, file a nil return by the 19th.
• Inactive scheme: Ask HMRC to mark the scheme inactive for the relevant period, subject to approval.

The inactivity request is intended for a contractor expecting no CIS activity for six months. For example, if work stops after the 6 April to 5 May period, request inactivity before the next affected filing date rather than allowing the 19 May deadline to pass. If HMRC approves the request, follow its stated period and retain the confirmation. Payments made during that period require the correct return instead.

Review the decision every month. A contractor that resumes payments must not rely on an old inactivity request or submit a nil return that hides actual payments.

From 6 April 2026, a quiet month requires a filing decision.

Before each 19th, check payments, confirm the scheme status and keep evidence for the choice made. Old advice that “no payments means no return” is incomplete for an active scheme.

Penalties and consequences for missing the deadline

A contractor can face a CIS penalty even when no tax was deducted. HMRC treats the CIS300 filing obligation separately from the amount paid to subcontractors, so an active scheme may still need a nil return by the 19th.

A CIS300 received after the 19th is late. HMRC issues an automatic fixed penalty for a late return and can apply further penalties when the failure continues. Check the current CIS penalty table and reasonable-excuse criteria before appealing, then file the outstanding return immediately to stop the problem growing. Do not rely on an old spreadsheet or a subcontractor's assumption that no payment means no filing.

Filing and payment create different risks

Late filing creates a CIS return penalty, including where no subcontractors were paid. Late payment of deductions is a separate compliance failure and may bring interest or other charges. Submitting the return does not settle the payment obligation, and paying HMRC does not replace the return.

For example, if the return for the 6 May to 5 June tax month is missed on 19 June, file it as soon as the figures are reconstructed. Do not wait for the next 19th. A second missed deadline creates a backlog and leaves less time to identify incorrect deductions, missing subcontractors or a return that should have been nil.

Use this recovery process:

1. Identify the tax month: Confirm the missing 6th-to-5th period and its 19th filing date.
2. Reconstruct the figures: Check bank payments, invoices, verification records and subcontractor details.
3. Submit or correct: File the accurate CIS300. Use a nil return only when the period had no reportable payments.
4. Check HMRC notices: Separate the filing penalty from payment interest or another charge.
5. Assess an appeal: Review the reasonable-excuse criteria and retain evidence supporting the explanation.
6. Prevent repetition: Set an internal draft date before the 19th and assign one named owner.

The deadline is predictable, so the penalty is avoidable. Treat each 19th as a controlled submission date, not an administrative task to recover after the month has already closed.

A simple monthly routine to stay compliant every tax month

Run CIS through a fixed routine rather than memory. The two diary markers are the 5th, when the tax month closes, and the 19th, when the return must reach HMRC.

Weekly controls

Collect subcontractor invoices, payment confirmations and CIS verification details every week. If a subcontractor's gross payment status or verification evidence is missing, chase it immediately. Waiting until the 6th creates a compressed reconciliation period.

Keep one digital folder for each tax month. Store the payment record, deduction calculation, verification evidence and CIS submission confirmation together. Your accounting software can help, but it won't repair incomplete source information.

The 6th and 14th checkpoints

On the 6th, reconcile the closed period against the bank account and subcontractor ledger. For the May tax month, that means checking payments made from 6 May to 5 June before preparing the return due on 19 June.

By the 14th, draft the return. Review the subcontractor list, payment totals and deductions, then resolve discrepancies while there's still time. The 19th should be a controlled submission, not the first moment you open the records.

5th lock, 14th draft, 19th submit.

Quiet months need a decision

If the reconciliation shows no subcontractor payments, don't abandon the task. From 6 April 2026, an active scheme generally requires a nil return, while a contractor expecting a genuine six-month inactive period can consider an approved inactivity request through HMRC's online service.

Review the scheme status annually, confirm subcontractor details, and retain supporting records in an organised archive. If you want an external team to handle subcontractor verification, monthly reconciliation and digital CIS submission, Stewart Accounting Services' CIS support is one option to assess alongside accounting software or an internal payroll process.

Set recurring calendar alerts for the 5th, 14th and 19th, assign a backup reviewer, and keep submission confirmations with the monthly records. That routine removes the Friday-night scramble and makes the CIS monthly return deadline a managed process rather than a monthly surprise.

If your CIS process still depends on someone remembering the 19th, review it before the next tax month closes. Contact Stewart Accounting Services to discuss subcontractor verification, monthly reconciliation and CIS return submission, then put a clear 5th, 14th and 19th control cycle in place.