One missed deadline, one hundred pound penalty
The CIS penalty clock starts ticking on the 20th of every month. A contractor who has not filed the previous month's CIS300 by the 19th is immediately in penalty territory. The construction industry generates more HMRC late-filing penalties per sector than almost any other, partly because CIS300 is a monthly return (not annual), and partly because the nil-return obligation reinstated from 6 April 2026 catches contractors who assume they have nothing to report.
This calendar sets out every CIS deadline for 2026/27 in a format you can refer to throughout the year.
How the CIS tax month works
CIS tax months do not align with calendar months. Each tax month ends on the 5th of the following calendar month. The return covering payments made between 6 April and 5 May is the "April" return, due by 19 May. The return covering 6 May to 5 June is due by 19 June, and so on.
Payment of deducted CIS to HMRC is due by:
- 22nd of the following tax month (electronic payment: bank transfer, BACS, Faster Payments)
- 19th of the following tax month (cheque or postal order)
For most contractors, electronic payment is the norm. The 22nd date matters: if funds do not clear HMRC's account by the 22nd, a late-payment interest charge applies.
All 12 CIS300 deadlines for 2026/27
| Tax month covered | Period end | CIS300 filing deadline | Electronic payment by |
|---|---|---|---|
| April 2026 | 5 May 2026 | 19 May 2026 | 22 May 2026 |
| May 2026 | 5 June 2026 | 19 June 2026 | 22 June 2026 |
| June 2026 | 5 July 2026 | 19 July 2026 | 22 July 2026 |
| July 2026 | 5 August 2026 | 19 August 2026 | 22 August 2026 |
| August 2026 | 5 September 2026 | 19 September 2026 | 22 September 2026 |
| September 2026 | 5 October 2026 | 19 October 2026 | 22 October 2026 |
| October 2026 | 5 November 2026 | 19 November 2026 | 22 November 2026 |
| November 2026 | 5 December 2026 | 19 December 2026 | 22 December 2026 |
| December 2026 | 5 January 2027 | 19 January 2027 | 22 January 2027 |
| January 2027 | 5 February 2027 | 19 February 2027 | 22 February 2027 |
| February 2027 | 5 March 2027 | 19 March 2027 | 22 March 2027 |
| March 2027 | 5 April 2027 | 19 April 2027 | 22 April 2027 |
The December return is the most commonly missed. The 19 December deadline falls in the run-up to Christmas shutdown, and contractors who go on site-closure before mid-December often miss it. Set a calendar reminder for the 15th of each month to check your filing status and leave four days to resolve any issues before the deadline. For a full breakdown of monthly return obligations, see our guide to the CIS monthly return.
Nil returns: the reinstated obligation from April 2026
From 6 April 2026, a CIS300 nil return is required in any month where no payments to subcontractors were made. This obligation was removed in 2015 and has been reinstated. Contractors who assumed the nil-return requirement still did not exist are now accumulating late-filing penalties without realising it.
There are two ways to meet the nil return obligation:
- File a nil CIS300 return for that month by the 19th, using the HMRC online service or CIS-compatible software.
- Pre-notify HMRC of inactivity for a specified period, which suspends the monthly filing requirement for the declared inactive months.
Pre-notification is the more practical route for contractors with seasonal stop-start patterns (for example, those who work June to November and are inactive December to May). One pre-notification covers multiple months. The notification must be made before the inactivity period begins. For a detailed walkthrough of the nil return process, see our guide to CIS nil returns explained.
The CIS300 penalty ladder
The penalty for a late CIS300 return escalates with the length of the delay. It applies per return, not per year. A contractor with three months of late returns has three separate penalty positions running simultaneously.
| Lateness from filing deadline | Penalty |
|---|---|
| 1 day late | £100 |
| 2 months late | £200 |
| 6 months late | £300 or 5% of the CIS liability (whichever is higher) |
| 12 months late | £300 or 5% of the CIS liability (whichever is higher); up to £3,000 or 100% where information is withheld deliberately |
The 12-month escalation point is particularly dangerous for contractors who avoid addressing late returns. A return that has been outstanding for a year can attract a penalty equal to 100% of the CIS deductions that should have been reported. On a return covering £5,000 of CIS deductions, that is a £5,000 penalty on top of the deductions themselves. For a full breakdown of how penalties accumulate and how to appeal, see our guide to CIS penalties and appeals.
Self Assessment deadlines for CIS subcontractors (2026/27)
| Tax year | Online filing deadline | Paper filing deadline | Payment deadline |
|---|---|---|---|
| 2025/26 (ending 5 April 2026) | 31 January 2027 | 31 October 2026 | 31 January 2027 |
| 2026/27 (ending 5 April 2027) | 31 January 2028 | 31 October 2027 | 31 January 2028 |
The 31 January deadline is the latest legal date, not the recommended date. A sole-trader CIS subcontractor who files in April or May rather than the following January receives any refund due months earlier. HMRC processes repayments within approximately 5 to 10 working days of a correctly filed online return. Filing in April versus January is the difference between a refund arriving in May and one arriving in February, a wait of roughly nine months for the same money.
Late Self Assessment filing carries a £100 immediate penalty, with further charges at 3, 6, and 12 months. These are separate from and do not interact with the CIS300 penalty ladder above. For the full Self Assessment process as a CIS subcontractor, see our guide to CIS and Self Assessment. To estimate your refund before you file, try the CIS Self Assessment calculator.
MTD quarterly update deadlines for 2026/27
Making Tax Digital for Income Tax applies to sole traders and partnerships from April 2026 if their annual income exceeds £50,000. For CIS subcontractors, income for the MTD threshold is measured as gross income before expenses and before CIS deductions. A subcontractor who received £42,000 net after 20% deductions but had £52,500 gross is above the £50,000 threshold and must comply.
Quarterly update deadlines for 2026/27:
| Quarter covers | Quarter end | Quarterly update deadline |
|---|---|---|
| 6 April 2026 to 5 July 2026 | 5 July 2026 | 7 August 2026 |
| 6 July 2026 to 5 October 2026 | 5 October 2026 | 7 November 2026 |
| 6 October 2026 to 5 January 2027 | 5 January 2027 | 7 February 2027 |
| 6 January 2027 to 5 April 2027 | 5 April 2027 | 7 May 2027 |
The deadline is the 7th of the month following the quarter end, not the 5th (which is the period end only). HMRC will not issue penalty points for late quarterly updates in 2026/27 as part of the first-year grace. However, the grace covers quarterly-update penalty points only. Late annual returns and late-payment penalties apply in full from day one. For a full explanation of MTD and CIS, see our guide to MTD for income tax and CIS.
Gross Payment Status: the compliance review window
GPS is not a one-time award. HMRC reviews compliance on an ongoing basis and can revoke GPS at any point within a 12-month compliance window. From 6 April 2026, Finance Act 2026 introduced a tougher GPS regime with the following key features:
- Immediate revocation without advance notice where a contractor knew or should have known about fraudulent connections in the supply chain.
- Five-year reapplication ban (previously one year) where GPS is removed on fraud grounds.
- Knowledge-based penalties under FA 2004 ss.62A/62B: 20% of the payment for payments made in the knowledge of deliberate CIS failures by a connected party.
The three due-diligence steps that protect GPS holders throughout the year are:
- Re-verify the CIS status of each subcontractor before each payment using the HMRC online verification service.
- Carry out a Companies House legitimacy check for each company subcontractor.
- Verify bank account name against the registered entity before transferring funds.
These steps must be carried out before every payment, not just at year end. There is no fixed "GPS review date" in the calendar: the compliance assessment runs continuously. Maintaining a record of each due-diligence check, including the date, the result, and the payment made, is the practical requirement.
Public sector CIS exemption from April 2026 (Regulation 24ZA)
A new exemption applies from 6 April 2026 under Regulation 24ZA: payments made to local authorities and public sector bodies are fully outside CIS. Contractors working on public sector contracts no longer apply CIS deductions to those payments and do not include them in the monthly CIS300 return.
The practical deadline implication: a contractor whose only subcontractor payments in a month are to public sector bodies (which are now excluded) must still file a CIS300 for that month. Because the public sector payments are excluded, the return will be a nil return. The nil return is due by the 19th as normal.
Summary: all deadlines at a glance
| Obligation | Deadline | Applies to |
|---|---|---|
| CIS300 monthly return (each month) | 19th of the following tax month | Contractors |
| CIS300 nil return (no payments made) | 19th of the following tax month (from April 2026) | Contractors |
| CIS payment to HMRC (electronic) | 22nd of the following tax month | Contractors |
| CIS payment to HMRC (cheque) | 19th of the following tax month | Contractors |
| Self Assessment online return (2025/26) | 31 January 2027 | Sole-trader subcontractors |
| Self Assessment paper return (2025/26) | 31 October 2026 | Sole-trader subcontractors |
| Self Assessment online return (2026/27) | 31 January 2028 | Sole-trader subcontractors |
| MTD quarterly update Q1 | 7 August 2026 | Sole traders above £50k gross |
| MTD quarterly update Q2 | 7 November 2026 | Sole traders above £50k gross |
| MTD quarterly update Q3 | 7 February 2027 | Sole traders above £50k gross |
| MTD quarterly update Q4 | 7 May 2027 | Sole traders above £50k gross |
| GPS due-diligence (three steps) | Before every subcontractor payment | GPS-holding contractors |
The most important single action for a contractor is putting the 19th of every calendar month in a shared calendar or diary system as a recurring CIS reminder. The penalty for a day-late return is £100. The cost of a recurring reminder is nothing.
If you are a subcontractor rather than a contractor, the deadline that matters most to you is Self Assessment (31 January, filed as early as possible from 6 April). For a detailed guide to the Self Assessment process as a CIS subcontractor, including the most common errors that delay refunds, see our guide to CIS monthly returns and our guide to CIS penalties and how to appeal them.