The clock is ticking. On 31 March 2026, HMRC will permanently shut down its free online CT600 filing service. If you're a company director who's been relying on HMRC's free tool to file your corporation tax return, you need to act now — or face serious consequences.
This isn't a drill. HMRC confirmed the closure in their official communications, and there will be no extension. After that date, you'll need third-party software or an accountant to file your CT600.
Here's exactly what you need to do, step by step, before the deadline hits.
Why Is HMRC Closing Its Free CT600 Filing Service?
HMRC has been gradually moving away from maintaining its own filing software. The free CT600 filing tool — officially known as HMRC's Company Tax Return service — has been available for years, allowing directors of small companies to file directly without paying for software or an accountant.
But maintaining this service costs HMRC millions. As part of their digital transformation strategy, they're outsourcing the filing interface to the private sector. From 1 April 2026 onwards, all CT600 submissions must go through HMRC-recognised commercial software.
This means:
- No more free filing through HMRC's own portal
- No grace period — the cutoff is hard on 31 March 2026
- All companies must use third-party software, regardless of size
- iXBRL accounts must still accompany every CT600 (as before)
If you haven't filed your current return yet, or if your filing deadline falls after March 2026, you need a plan right now.
Who Is Affected?
Every UK limited company that files a CT600 is affected. But the impact hits hardest for:
Solo Directors and Micro-Companies
If you've been using HMRC's free service to avoid accountant fees, you're the most affected. You'll need to find and set up alternative software before your next filing deadline.
Companies with Accounting Periods Ending After June 2025
If your company's accounting period ends after 30 June 2025, your 12-month filing deadline will fall after 31 March 2026. That means you cannot use HMRC's free tool — even if you were planning to.
Dormant Companies
Yes, even dormant companies must file a CT600 (a nil return). The free service closure affects you too.
First-Time Directors
If you've just incorporated and haven't filed a CT600 before, you won't even have the option of using HMRC's free tool. You'll need to start with commercial software from day one. Check our beginner's guide to CT600 filing for a complete walkthrough.
What Happens If You Don't File?
Let's be absolutely clear about the penalties:
Late Filing Penalties
| How Late | Penalty |
|---|---|
| 1 day late | £100 |
| 3 months late | Another £100 |
| 6 months late | HMRC estimates your tax + 10% penalty on that |
| 12 months late | Another 10% of estimated tax |
These penalties are automatic. HMRC doesn't send a warning — the fine is applied the moment you miss your deadline.
Interest Charges
On top of penalties, HMRC charges daily interest on any unpaid corporation tax. The current interest rate on late payments is 7.25% — and it compounds. The longer you wait, the more you owe.
Compliance Actions
Miss enough deadlines and HMRC may:
- Open a compliance check (investigation) into your company
- Issue a determination — where they estimate your tax liability (usually higher than reality)
- Flag your company for future scrutiny
None of this is worth the risk. Filing is mandatory, and the tools to do it are affordable.
Your Step-by-Step Action Plan (Do This Now)
Here's exactly what you need to do before 31 March 2026:
Step 1: Check Your Filing Deadline
Your CT600 filing deadline is 12 months after the end of your company's accounting period. For example:
- Accounting period ends 31 March 2025 → Filing deadline: 31 March 2026
- Accounting period ends 30 June 2025 → Filing deadline: 30 June 2026
If your deadline falls on or before 31 March 2026, you can still use HMRC's free service — but don't wait until the last day.
If your deadline falls after 31 March 2026, you must use commercial software.
Not sure about your deadline? Check your Companies House profile or log in to your HMRC business tax account.
Step 2: Gather Your Financial Records
Before you can file, you need:
- Profit and loss account for the accounting period
- Balance sheet as at the period end date
- Bank statements (to reconcile your figures)
- Records of all income and expenses
- Details of any capital expenditure (equipment, vehicles, etc.)
- Dividend records (if you paid yourself dividends)
- Director's loan account details (if applicable)
If you use accounting software like Xero, QuickBooks, or FreeAgent, most of this data is already recorded. You just need to make sure it's complete and accurate.
Step 3: Choose Your CT600 Filing Method
You have three options:
Option A: Use Software Like Taxpipe (Recommended)
Cost: £59 per filing
Taxpipe is purpose-built for company directors who want to file their own CT600 without an accountant. Here's why it's the obvious replacement for HMRC's free service:
- Guided step-by-step process — no tax knowledge needed
- Automatic iXBRL generation — the technical format HMRC requires
- CT600 + accounts filed together — one submission, everything handled
- Real-time HMRC validation — catch errors before you submit
- £59 flat fee — no subscriptions, no hidden costs
Compare that to the alternatives:
- Accountant: £200–£500+ per year for a basic CT600 filing
- Other software: £100–£300+ with complex interfaces designed for accountants
Option B: Hire an Accountant
If your company has complex tax affairs — multiple income streams, R&D claims, group structures — an accountant may make sense. But for a straightforward limited company with simple trading income, you're paying £300+ for something you can do yourself in under an hour.
See our full cost comparison for a detailed breakdown.
Option C: Use Other Commercial Software
There are other HMRC-recognised CT600 software providers. However, many are designed for accountants, not directors. They're often more expensive and harder to use. We've written a detailed comparison of CT600 software options to help you decide.
Step 4: File Before the Deadline
Don't wait. Here's why:
- Technical issues happen — HMRC's systems occasionally go down near deadlines
- Errors in your return may need time to correct
- You'll sleep better knowing it's done
If you're using Taxpipe, the entire process takes 30–60 minutes for a typical small company:
- Create your account
- Enter your company details (auto-populated from Companies House)
- Enter your financial figures
- Review the auto-generated CT600 and iXBRL accounts
- Submit directly to HMRC
- Receive your confirmation
File your CT600 with Taxpipe for £59 →
Step 5: Pay Your Corporation Tax
Filing and paying are separate. Your CT600 tells HMRC how much tax you owe. You then need to pay that amount within 9 months and 1 day of your accounting period end.
For example: accounting period ends 31 March 2025 → payment due by 1 January 2026.
Read our complete guide to paying corporation tax for all payment methods.
What If You've Already Missed a Deadline?
If you're reading this and realising you've already missed a filing deadline, don't panic — but do act immediately.
File Now, Even If It's Late
A late filing is always better than not filing at all. The penalties continue to accumulate the longer you wait. File as soon as possible to stop the clock.
You May Be Able to Appeal
If you have a reasonable excuse for filing late — such as serious illness, a natural disaster, or HMRC's own systems being unavailable — you can appeal the penalty. But "I didn't know about the deadline" is generally not accepted.
Consider Amending Previous Returns
If you've filed previous CT600s with errors, you can amend them within 12 months of the original filing deadline. This could save you money if you overclaimed or underclaimed expenses.
Timeline: Key Dates You Must Know
| Date | What Happens |
|---|---|
| Now – 30 March 2026 | HMRC's free CT600 service still available |
| 31 March 2026 | Free service closes permanently |
| 1 April 2026 onwards | All filings must use commercial software |
| Your company's deadline | 12 months after accounting period end — check yours now |
How Taxpipe Replaces the HMRC Free Service
Taxpipe was built specifically for directors who were using HMRC's free filing service. Here's how we compare:
| Feature | HMRC Free Service | Taxpipe |
|---|---|---|
| Cost | Free (ending March 2026) | £59 per filing |
| iXBRL accounts | You had to create separately | Generated automatically |
| Guided walkthrough | Basic | Step-by-step with help text |
| Error checking | Minimal | Real-time validation |
| Support | None | Email support included |
| Available after March 2026 | ❌ No | ✅ Yes |
The transition from HMRC's free tool to Taxpipe is straightforward. If you could use HMRC's system, you can use Taxpipe — it's designed to be easier, not harder.
What About Dormant Companies?
If your company is dormant (not trading), you still need to file:
- A CT600 nil return with HMRC
- Dormant accounts with Companies House
Taxpipe handles dormant company filings too. The process is even simpler — enter your company details, confirm no trading activity, and submit. Still just £59.
Don't Leave It Until the Last Minute
Here's what happens every year on the final day before major HMRC deadlines:
- HMRC systems slow to a crawl
- Commercial software support queues are hours long
- Directors panic-file with errors that trigger compliance checks
File at least 2 weeks before your deadline. If there's an error, you'll have time to correct and resubmit.
Use the Taxpipe Calculator to See What You Owe
Not sure how much corporation tax your company owes? Our free CT600 calculator gives you an instant estimate. Enter your revenue, expenses, and we'll show you:
- Your estimated corporation tax liability
- Which CT600 boxes your figures go in
- Whether you qualify for any reliefs
FAQ
When does HMRC's free CT600 filing service close?
HMRC's free Company Tax Return filing service closes permanently on 31 March 2026. After this date, all companies must use HMRC-recognised commercial software or an accountant to file their CT600.
What is the cheapest way to file a CT600 after March 2026?
The most affordable option is Taxpipe at £59 per filing. This includes your CT600 return and iXBRL-tagged accounts submitted directly to HMRC. Accountants typically charge £200–£500+ for the same service.
Can I still file my CT600 for free?
Only until 31 March 2026, using HMRC's own service. After that date, the free option no longer exists. Taxpipe at £59 is the closest affordable alternative.
What happens if I miss my CT600 filing deadline?
You'll receive an automatic £100 penalty immediately. After 3 months, another £100. After 6 months, HMRC can estimate your tax bill and charge 10% on top. After 12 months, another 10%. Plus interest on any unpaid tax at 7.25%.
Do dormant companies need to file a CT600?
Yes. Even if your company has no trading activity, you must file a CT600 nil return with HMRC and dormant accounts with Companies House. Failure to file results in the same penalties as trading companies.
How long does it take to file a CT600 with Taxpipe?
Most directors complete their CT600 filing in 30–60 minutes using Taxpipe. The guided process walks you through each section, and iXBRL accounts are generated automatically.
Is Taxpipe HMRC-recognised software?
Yes. Taxpipe is recognised by HMRC for CT600 filing and submits your return directly to HMRC via their secure API. You'll receive an official acknowledgement from HMRC confirming your submission.
Take Action Now
The deadline is real. The closure is confirmed. And the solution is simple.
- Check your filing deadline — do it today
- Sign up for Taxpipe — takes 2 minutes
- File your CT600 — guided process, about 30-60 minutes
- Pay your tax — separately, by the payment deadline
Don't be one of the thousands of directors who'll be scrambling for a solution on 1 April 2026. Get ahead of it now.
File your CT600 for £59 with Taxpipe →