CIS returns: monthly CIS300 deadlines for contractor clients

Written by the Mipp team

Published: 19 October 2026 | Last checked against GOV.UK: 19 October 2026 | Accurate as of October 2026

A CIS return, form CIS300, is the monthly return a Construction Industry Scheme contractor sends HMRC. It lists what they paid each subcontractor in the tax month and what they deducted. It must reach HMRC by the 19th of the month after the tax month ends, and a tax month runs from the 6th of one month to the 5th of the next. A contractor files every month, even when they paid no subcontractors, and a late return costs £100 from the first day.

This guide is for small UK practices that file CIS returns for contractor clients. It covers the deadlines to June 2027, weekends, nil returns, penalties, and a monthly routine you can run for every contractor on your books.

Who has to file CIS returns

A business must register as a CIS contractor if it pays subcontractors to do construction work. That includes builders, labour agencies, gangmasters and property developers. A business that doesn't do construction work also counts, as a "deemed" contractor, if it has spent more than £3 million on construction in the 12 months since its first payment. Contractors can be sole traders, partnerships or limited companies.

Once registered, a contractor must verify new subcontractors with HMRC, make deductions at the rate HMRC gives, pay those deductions to HMRC and file a monthly return.

CIS return deadlines to June 2027

The return is due by the 19th of the month after the tax month ends. The deductions must be paid by the 22nd if paid electronically, or the 19th if paid by post.

The March to April return is still due on 19 April. The tax year turns over on 6 April, but the return deadline doesn't move.

When the 19th falls at a weekend

GOV.UK says the return must reach HMRC by the 19th and gives no weekend extension for it. Plan to file by the Friday before, which is 18 December 2026 and 18 June 2027 in this period. For payments, card payments and Faster Payments can reach HMRC at weekends, but Bacs and cheques need extra time. Our UK tax deadlines calendar for 2026-27 covers the weekend rules for each payment method.

Nil returns and inactivity requests

GOV.UK says contractors should file CIS returns every month. If a client paid no subcontractors in a tax month, they must do one of two things:

• File a nil return, showing payments of 0.
• Make an inactivity request, telling HMRC they have temporarily stopped using subcontractors. A contractor who expects to make no payments for up to 6 months can ask for the scheme to be made inactive. HMRC then sends no returns for that period, and the contractor must file again once they start paying subcontractors.

The nil return is the one that gets forgotten, because nothing happened that month. It carries the same £100 penalty as any other late return.

Penalties for a late CIS return

Returns later than that can attract a further penalty of up to £3,000 or 100% of the CIS deductions on the return, whichever is higher. Separately, a contractor can be fined up to £3,000 for giving the wrong employment status for a subcontractor on the return. An appeal must be made within 30 days of the date on the penalty notice.

What goes into each month's return

For each subcontractor paid in the tax month, the return shows the payment and any deduction. The contractor also declares that the subcontractors listed are not employees. Before the return can be completed:

• New subcontractors must be verified with HMRC before they are first paid. HMRC gives the deduction rate: 20% for registered subcontractors, 30% for unregistered ones, or 0% with gross payment status. Subcontractors used before must be verified again if they haven't been on a return in the current or last 2 tax years.
• Payment and deduction statements go to each subcontractor whose payment had a deduction, within 14 days of the end of the tax month. For the tax month ending 5 June, that's by 19 June, the same day as the return.

Returns are filed through HMRC's CIS online service or commercial CIS software.

A monthly CIS routine for a small practice

With several contractor clients, the same five steps repeat every month:

The step that slips is the client who "had nothing this month". Keep a nil return on the list like any other, so it can't fall off.

Tracking every contractor client's CIS returns in Mipp

In Mipp, tick CIS contractor on a client's compliance details. Mipp then schedules a CIS300 for each tax month, named by its dates (for example "CIS300 6 Oct to 5 Nov 2026") and due on the 19th, plus a CIS payment date on the 22nd. They appear on the CIS tab of the Compliance view, next to the client's other deadlines, and as tasks on that client's board. You can also subscribe to Mipp's private calendar feed to see them in Google, Outlook or Apple calendars.

Each return moves through stages from To do to Submitted. A month with no subcontractor payments can be marked Nil return, which counts as complete. If a client stops being a contractor, untick the box: Mipp removes future months you haven't started, and keeps filed, nil and overdue ones so a missed return isn't lost.

Mipp tracks the deadlines. It doesn't file returns, verify subcontractors, work out deductions, record whether the client has paid HMRC, or email your clients. See how this fits into Mipp's practice management software for accountants.

Deadline dates in Mipp are a planning aid, calculated from the information you enter using standard UK rules. Always check them against HMRC.

Subcontractor clients

Mipp only schedules CIS returns for contractors. If you prepare Self Assessment returns for subcontractors, their payment and deduction statements are part of the records you need. They're on the sole trader list in our Self Assessment reminder letter templates.

Frequently asked questions

When is the CIS return due?

By the 19th of the month after the tax month ends. A tax month runs from the 6th to the 5th, so the return for 6 October to 5 November 2026 is due by 19 November 2026.

What is a CIS300?

CIS300 is HMRC's monthly return for Construction Industry Scheme contractors. It lists each subcontractor paid in the tax month and any deduction made.

Do I need to file a CIS return if no subcontractors were paid?

Yes. File a nil return, or tell HMRC the contractor has temporarily stopped using subcontractors (an inactivity request).

What is the penalty for a late CIS return?

£100 if it's one day late, £200 at 2 months, and £300 or 5% of the deductions on the return, whichever is higher, at 6 and 12 months. Later returns can attract up to £3,000 or 100% of the deductions.

Does the CIS return deadline move at the weekend?

GOV.UK gives no weekend extension for the return, which must reach HMRC by the 19th. 19 December 2026 is a Saturday, so plan to file by Friday 18 December.

Track every contractor client's CIS300 in Mipp

Tick CIS contractor once and every month's return is on your list, nil months included. Start a 14-day free trial. You add a card to start, and nothing is charged for 14 days. Cancel anytime. See pricing for plans. For the wider calendar, see the UK tax deadlines for 2026-27.

Sources

All checked on Monday 19 October 2026. Accurate as of October 2026.

1. GOV.UK, What you must do as a CIS contractor (overview, who is covered, verify subcontractors, deductions, paying HMRC, monthly returns). https://www.gov.uk/what-you-must-do-as-a-cis-contractor
2. GOV.UK, File your monthly returns (deadlines, nil returns, penalties). https://www.gov.uk/what-you-must-do-as-a-cis-contractor/file-your-monthly-returns
3. GOV.UK, Pay deductions to HMRC. https://www.gov.uk/what-you-must-do-as-a-cis-contractor/pay-deductions-to-hmrc
4. GOV.UK, Pay employers' PAYE (payment methods and timings). https://www.gov.uk/pay-paye-tax