The key CIS tax return deadline for the 2024/25 tax year is 31 January 2026. Miss it and HMRC charges £100 automatically — even if you owe nothing.
Self Assessment Deadlines (Subcontractors)
For the 2024/25 tax year:
| What | Deadline |
|---|---|
| Register for Self Assessment | 5 October 2025 (first year only) |
| Online tax return | 31 January 2026 |
| Pay tax owed | 31 January 2026 |
| Second payment on account | 31 July 2026 (if applicable) |
For the 2025/26 tax year: online return and payment both due 31 January 2027.
File early: You can submit from 6 April — the earlier you file, the sooner your refund arrives.
Monthly CIS Return Deadlines (Contractors)
If you're a contractor who pays subcontractors, you must file monthly CIS returns by the 19th of each month (covering the 6th of the previous month to the 5th of the current month). Payment is due by the 22nd electronically. Even months with no subcontractor payments require a nil return.
What Happens If You Miss a Deadline?
Late Filing Penalties (Self Assessment)
| How Late | Penalty |
|---|---|
| 1 day late | £100 (automatic) |
| 3 months late | £10 per day for up to 90 days (max £900) |
| 6 months late | £300 or 5% of tax due (whichever is greater) |
| 12 months late | £300 or 5% of tax due (in serious cases up to 100% of tax due) |
These penalties apply even if you owe no tax. For a full breakdown of what happens next, read what happens if you don't file your CIS tax return.
Late Payment Interest
HMRC charges interest from the due date (Bank of England base rate + 2.5%), plus surcharges of 5% of outstanding tax at 30 days, 6 months, and 12 months late.
Contractor Late Filing Penalties
Contractors face separate penalties for late monthly CIS returns: £100 on day one, rising to £200 at 2 months, and additional charges at 6 and 12 months. Penalties stack and can reach £900+ per return.
Making Tax Digital Deadlines (From April 2026)
From 6 April 2026, CIS subcontractors earning over £50,000 gross must submit quarterly digital updates under Making Tax Digital instead of one annual return. Deadlines for 2026/27:
| Submission | Period | Deadline |
|---|---|---|
| Q1 Update | 6 Apr – 5 Jul 2026 | 7 August 2026 |
| Q2 Update | 6 Jul – 5 Oct 2026 | 7 November 2026 |
| Q3 Update | 6 Oct – 5 Jan 2027 | 7 February 2027 |
| Q4 Update | 6 Jan – 5 Apr 2027 | 7 May 2027 |
| Final Declaration | Full year review | 31 January 2028 |
Under the new MTD penalty system, each late quarterly update earns a penalty point. At 4 points, you get a £200 penalty. However, HMRC has confirmed a grace period for the first 12 months — no penalty points for late quarterly updates between April 2026 and April 2027.
What If I've Already Missed a Deadline?
File as soon as possible — every day you delay could mean additional penalties. If you need help with the filing process, follow our step-by-step guide on how to claim your CIS tax refund. If you have a reasonable excuse (serious illness, bereavement, HMRC system failure), you can appeal the penalty. "I forgot" or "I didn't know" are not considered reasonable excuses.
Need to catch up? Our CIS tax refund calculator can show you what you're owed — and filing your return is the first step to getting that money back.
Related Guides
- What Happens If You Don't File Your CIS Tax Return? — Penalties, interest, and how to fix things if you've missed a deadline
- How to Claim Your CIS Tax Refund — Step-by-step guide to filing your return and claiming your refund
- Making Tax Digital for CIS Subcontractors — New quarterly deadlines and what changes from April 2026
Frequently Asked Questions
When is the CIS tax return deadline?
The Self Assessment deadline for CIS subcontractors is 31 January following the end of the tax year. For the 2024/25 tax year, that's 31 January 2026.
Can I file my CIS tax return early?
Yes. You can file as soon as the tax year ends on 5 April. Filing early gets your refund faster.
What's the penalty for a late CIS tax return?
An automatic £100 penalty applies if your return is even one day late. After 3 months, you'll also face £10 per day penalties. After 6 and 12 months, further penalties of £300 or 5% of tax due apply.
Do I still file a Self Assessment after MTD starts?
Your Final Declaration under MTD replaces the traditional Self Assessment return. It's filed through MTD-compatible software rather than the HMRC online Self Assessment system.
Last updated: October 2025. Check GOV.UK for the most current deadline information.