Here’s how it usually goes. You’re halfway through a normal week, invoices still need chasing, receipts are sitting in a shoebox somewhere, and then someone brings up a date: 30th September. For a lot of UK company directors, that one date decides whether the next few months feel calm or feel like a scramble.
If your private limited company’s financial year ended 31st December 2025, there’s a good chance 30th September 2026 is your Company Accounts Filing Deadline. Miss it and Companies House won’t send a gentle reminder first. It goes straight to an automatic penalty, starting at £150 and rising to £1,500 the longer your accounts stay unfiled.
Here’s the annoying part. This deadline isn’t the same for every company, even ones that look almost identical on paper. Your accounting reference date, whether these are your first accounts, and whether you’ve ever changed your year-end, can all move the date around. So before you write 30th September in your diary and move on, it’s worth checking how the rule actually works, and whether it even applies to you.
Quick Answer: Is Your Deadline 30th September?
If your private limited company’s financial year ended on 31st December 2025, your Company Accounts Filing Deadline is 30th September 2026. This is because private limited companies get nine months from their accounting reference date to file accounts with Companies House.
But that word “probably” matters. Companies that have changed their accounting reference date, or that are filing accounts for the first time, often end up with a different date. Treat the nine-month rule as a rough guide, not a fixed fact. Your real deadline is whatever Companies House has on record for your company, so it’s worth checking that directly instead of just assuming.
How the Companies House 9-Month Deadline Works
Every filing deadline is anchored to your accounting reference date, the date that marks the end of your financial year. For most private limited companies, that’s nine months. Public limited companies get less breathing room, at six.
One detail that trips people up: what counts is when Companies House actually receives acceptable accounts, not when you drop them in the post or hit send. Cutting it fine in the last few days is risky for exactly this reason, if your accounts get bounced back for being incomplete or incorrect, you may not get any grace period to fix and resubmit them before the clock runs out.
You can check your own accounting reference date and exact filing deadline free of charge on GOV.UK’s Companies House service, which is also the authoritative source for the rules referenced throughout this article.
Filing Method Changes in 2026: What’s Different Now
The deadline itself hasn’t changed, but how you file has. On 31 March 2026, Companies House permanently closed WebFiling for annual accounts, along with the joint CATO service that let small companies file accounts and Corporation Tax returns together through one HMRC portal. Paper and direct web-based filing routes for accounts are no longer accepted.
From 1 April 2026, all annual accounts must be submitted in iXBRL format using approved commercial accounting software, or through an agent who files on your behalf. This applies to every company in scope, including small and micro-entities and dormant companies. If you previously filed your own accounts by logging into the Companies House website, that route is no longer available, and you’ll need either accounts production software or professional support.
Separately, wider reforms that would have required small companies to publish fuller profit and loss information were paused in January 2026 and pushed back to April 2028, so that part of the picture hasn’t changed yet. It’s the filing mechanism, not the disclosure requirements, that shifted this year.
Private Limited Companies vs PLCs
The amount of time available for filing accounts depends on the type of company. Most small businesses operate as private limited companies, so the nine-month rule will usually apply. Public limited companies, or PLCs, normally have a shorter filing window.
| Feature | Private Limited Companies | PLCs |
| Normal filing period | 9 months after year-end | 6 months after year-end |
| Ownership | Privately owned | May offer shares to the public |
| Accounts filed with | Companies House | Companies House |
| Time to prepare accounts | Longer window | Shorter window |
| Maximum late filing penalty | £1,500 | £7,500 |
| Typical structure | Common among small businesses | Usually larger companies |
If you’re running a small private limited company, nine months is the number to remember. Still, a quick check of your official filing date beats relying on mental arithmetic.
Worked Example: 31 Dec Year-End → 30 Sept Filing Date
Say your accounting reference date is 31st December 2025. Add nine months, and here’s what that looks like:
- Accounting reference date: 31st December 2025
- Nine-month filing window: January to September 2026
- Company Accounts Filing Deadline: 30th September 2026
This is exactly why so many companies with a December year-end end up talking about the same late-September date. One thing worth knowing: where your accounting reference date falls on the last day of a month, Companies House generally rounds the filing deadline to the last day of the relevant month too, not to a specific numbered date.
Filing Your First Accounts as a New Company
If you’ve just incorporated, don’t assume the standard rule applies straight away. Companies House usually sets your first accounting reference date as the last day of the month in which your incorporation anniversary falls, which means your first accounting period can stretch beyond 12 months.
When that happens, a private company generally has to deliver its first accounts within 21 months of incorporation, or three months from the accounting reference date, whichever gives you longer. If your first accounts cover 12 months or less, the usual nine-month rule kicks back in.
This is one of the more common first-year mistakes: assuming your incorporation date and your accounts deadline are the same thing. They’re not, and it’s worth confirming your actual date early rather than working it out from memory later.
Companies House vs HMRC: The Three Deadlines You Actually Have
This is where things get genuinely confusing, because most directors think of “doing the accounts” as a single task with a single date. In reality, there are three separate deadlines running in parallel, going to two different places.
Annual accounts → Companies House → 9 months after year-end. Year-end 31st December 2026 means accounts are due by 30th September 2027.
Corporation Tax payment → HMRC → 9 months and 1 day after year-end. Same year-end, but the tax bill is due 1st October 2027, a day before your accounts deadline finishes. So yes, you may well need to pay Corporation Tax before you’ve even filed the return that explains the number.
CT600 Company Tax Return → HMRC → 12 months after year-end. For that same accounting period, the CT600 itself isn’t due until 31st December 2027.
| Requirement | Filed/Paid To | Typical Deadline |
| Annual accounts | Companies House | 9 months after year-end |
| Corporation Tax payment | HMRC | 9 months and 1 day after year-end |
| CT600 Company Tax Return | HMRC | 12 months after year-end |
| Confirmation statement | Companies House | Every 12 months, on a separate schedule from accounts |
A fourth date worth knowing about, even though it isn’t an accounts deadline, is the confirmation statement. This is a separate filing that confirms your company’s details are up to date, due every 12 months on its own schedule rather than tied to your year-end. It’s easy to conflate with the accounts deadline because both go to Companies House, but missing one doesn’t excuse missing the other.
The takeaway: ticking off one deadline doesn’t mean you’re done. Filing with Companies House says nothing about where you stand with HMRC.
If you want to see all of your company’s key dates in one place rather than tracking them separately, MyIVA’s Corporation Tax Deadline Checker works out your specific deadlines based on your year-end.
What Happens If You Miss the Deadline
Missing the Company Accounts Filing Deadline is something you should take seriously. Companies House can issue a late filing penalty automatically once accounts are delivered after the deadline.
Here are some of the possible consequences:
- The penalty is automatic. Companies House doesn’t wait to see if you have a good reason; it issues the penalty as soon as accounts arrive late.
- £150 for anything up to a month late, that is just the starting point for private companies.
- The longer you wait, the more it costs. £375, then £750, then £1,500 as the delay stretches out.
- Filing late two years running doubles the penalty. Companies House has little patience for repeat offenders.
- Unpaid penalties can trigger enforcement action.
- In the worst cases, the company risks being struck off the register for failing to file required documents at all.
- Directors themselves aren’t shielded. Beyond the civil penalty on the company, failing to meet filing obligations can be treated as a criminal offence.
The good news is that most of these problems are avoidable. Starting the accounts process early gives you time to find missing records, correct mistakes and make sure everything is ready before the Company Accounts Filing Deadline.
Can You Get More Time to File?
Yes, it may be possible to get more time, but an extension is not automatically granted.
Companies House allows a company to apply for extra time where an unplanned event has prevented it from filing on time. You must apply before your existing filing deadline passes, and the circumstances generally need to be exceptional.
Being busy, forgetting the date or relying on someone else to complete the accounts will not normally be enough. The reason for the delay needs to involve circumstances outside your control.
For that reason, it is much better to act early. If something unexpected happens and you believe it may stop you from meeting your Company Accounts Filing Deadline, look into an extension before the original deadline expires.
How MyIVA Can Support Your Accounts and Corporation Tax Deadlines
Now that WebFiling and CATO have closed, filing accounts yourself means sourcing commercial software and preparing iXBRL-tagged accounts correctly. MyIVA can handle that process for you, alongside your other Companies House and HMRC obligations.
1. Company Accounts Support
MyIVA can help prepare company accounts and organise the financial information needed for filing. This can help you approach your deadline with more confidence.
2. Corporation Tax Assistance
Corporation Tax has its own rules and payment dates. MyIVA can support you with your Corporation Tax obligations and help you understand what needs to be done.
3. CT600 Company Tax Returns
Preparing a CT600 requires accurate figures and supporting information. MyIVA can help with the process and keep your tax filing requirements organised.
4. Personal Tax and Self-Assessment
MyIVA also supports individuals and sole traders with MTD Tax Filing and Self-Assessment tax returns. Having professional support can make a complicated process easier to manage.
5. Help With Important Deadlines
Keeping track of Companies House and HMRC dates can be difficult. MyIVA can help you understand your obligations and prepare for key filing dates before they become urgent.
With the right support and better planning, your Company Accounts Filing Deadline does not have to become a last-minute problem.
FAQs: Frequently Asked Questions
Do I need an accountant to file company accounts?
You are not always legally required to use an accountant. However, many small business owners choose professional help to make sure their accounts are prepared correctly and deadlines are not missed, and since accounts must now be filed through commercial software rather than the Companies House website, many directors are finding it more practical to have an accountant handle the submission.
What if 30th September falls on a weekend or bank holiday?
The deadline does not automatically move to the next working day. Companies House says you must still ensure your accounts are delivered by the legal filing date, even if it falls on a Sunday or bank holiday.
Can I still file my own accounts online myself?
Not through Companies House WebFiling, which closed for accounts on 31 March 2026. You’ll need commercial accounts production software that supports iXBRL filing, or an accountant who files on your behalf.
Is the accounts deadline the same as my tax return deadline?
No. Annual accounts are filed with Companies House, while the CT600 Company Tax Return is filed with HMRC. Corporation Tax payment also has its own deadline.
What if my company is dormant?
A dormant company still normally needs to deliver accounts to Companies House. The filing requirements may be simpler, but being dormant does not automatically remove your accounts filing responsibilities, and dormant companies are also within scope of the 2026 iXBRL filing requirement.
How do I check my exact Company Accounts Filing Deadline?
You can check your company’s official filing date through Companies House, via the GOV.UK Companies House service. This is the safest way to confirm when your accounts are due.
Conclusion
For a lot of private limited companies with a 31st December 2025 year-end, 30th September 2026 is the date that matters most right now. But “probably” isn’t the same as “definitely.” First-year companies and anyone who’s changed their accounting period should double-check rather than assume.
And even once the accounts are filed, remember that Companies House and HMRC are keeping separate scorecards. Your annual accounts, your Corporation Tax payment, and your CT600 can all land on different dates within the same year.
If you’d rather not track all of this manually, MyIVA can help get your accounts, Corporation Tax, and CT600 filing organised well before the next deadline creeps up. Get in touch with MyIVA today.
