HMRC Free CT600 Deadline March 2026: Action Plan

HMRC's Free CT600 Service Is Closing — And the Clock Is Ticking

If you've just discovered that HMRC is retiring its free online Corporation Tax filing service on 31 March 2026, you're not alone. Thousands of UK company directors are finding out right now — and many are understandably worried.

The good news? You have options, and switching to a new filing method is simpler than you might think. This guide walks you through exactly what's happening, what it means for your company, and what to do next.

What's Actually Happening?

HMRC has announced that its free Corporation Tax online filing service — the one many directors have used for years to submit their CT600 returns — will permanently close on 31 March 2026.

After that date, you will no longer be able to:

• File your CT600 directly through HMRC's website
• Use the free HMRC software to prepare your return
• Submit corporation tax returns without third-party software

This affects every UK limited company, whether you're actively trading, dormant, or winding down.

Why Is HMRC Doing This?

HMRC has been gradually shifting to a model where third-party commercial software handles tax return preparation and submission. This aligns with the broader Making Tax Digital (MTD) programme. The free service was always basic — it lacked error-checking, auto-calculations, and the ability to handle complex returns.

Who Needs to Take Action?

Every limited company registered for Corporation Tax in the UK. Specifically:

• Active trading companies — you'll need software to file your next CT600
• Dormant companies — yes, you still need to file a nil return, and you'll need software to do it
• Companies with upcoming deadlines — if your filing deadline falls after 31 March 2026, you must use commercial software
• First-time filers — new companies incorporated now won't have access to the free service at all

Check Your Deadline

Your CT600 is due 12 months after the end of your accounting period. For example:

If your deadline is on or before 31 March 2026, you can still use the free service — but don't leave it to the last day.

Your Action Plan: What to Do Right Now

Step 1: Check Your Filing Deadline

Log in to your HMRC Business Tax Account and check when your next CT600 is due. If it's before 31 March 2026, you still have the option to use the free service — but act fast.

Step 2: Gather Your Documents

Whether you file through the old service or switch to new software, you'll need:

• Company accounts (profit and loss, balance sheet)
• Bank statements for the accounting period
• Records of all income and expenses
• Details of any capital allowances (equipment purchases, vehicles)
• Director's loan account balance (if applicable)
• Your company's UTR number and Companies House number

Step 3: Choose Your Filing Software

This is the big decision. Here's what to look for:

• HMRC-recognised — the software must be on HMRC's approved list
• iXBRL accounts generation — you need to submit tagged accounts alongside your CT600
• Auto-calculations — good software calculates your tax, including marginal relief
• Error checking — catches mistakes before submission
• Affordable — you shouldn't need to pay hundreds of pounds

Taxpipe is purpose-built for this exact situation. It's designed for directors who previously used HMRC's free service and need an affordable, straightforward alternative. You answer simple questions about your company, and Taxpipe handles the CT600, iXBRL accounts, and HMRC submission — all for a fraction of what an accountant charges. Check our pricing to see how it compares.

Step 4: Set Up Your Government Gateway

Whichever software you choose, you'll still need your HMRC Government Gateway credentials to authorise the submission. If you've been using the free service, you already have these. Keep them safe — you'll need them when your new software submits to HMRC.

Step 5: File a Test Return (If Time Allows)

If your next deadline isn't imminent, consider doing a trial run with your chosen software before the pressure is on. Most platforms (including Taxpipe) let you prepare your return and review it before submitting.

Common Questions

"Can I still file for free?"

Not after 31 March 2026 through HMRC directly. However, some software providers offer free tiers for very simple returns. Taxpipe offers competitive pricing that's far less than hiring an accountant — use our calculator to estimate your costs.

"What if I miss the deadline because of the switchover?"

HMRC has not indicated any grace period. If you file late, the standard penalties apply:

• 1 day late: £100 penalty
• 3 months late: another £100
• 6 months late: 10% of unpaid tax (minimum £300)
• 12 months late: a further 10% of unpaid tax

Don't assume HMRC will be lenient because their service closed. Switch to new software now.

"I have a dormant company — do I really need to bother?"

Yes. Dormant companies must still file a CT600 (a nil return) every year. After March 2026, you'll need software to do this. The good news is that nil returns are quick and simple with the right tool.

"What about my accountant?"

If you already use an accountant, they'll handle the transition for you — they already use commercial software. This change primarily affects directors who file their own returns.

"Is my data safe with third-party software?"

Reputable providers use bank-level encryption and are authorised by HMRC. At Taxpipe, your data is encrypted at rest and in transit, and we never share it with third parties.

Don't Wait Until March 31st

The worst thing you can do is leave this until the last minute. Here's why:

1. Server load — HMRC's systems slow down near deadlines as thousands of people try to file simultaneously
2. Learning curve — new software takes a little time to get comfortable with, even if it's simple
3. Missing documents — you might discover you're missing a bank statement or receipt
4. Support availability — software providers get swamped near deadlines

Our recommendation: switch to your new filing solution this week. Even if your return isn't due for months, getting set up now means you're ready when the time comes.

The Silver Lining

Here's the thing most articles won't tell you: the HMRC free service was actually quite poor. It had no auto-calculations, no error checking, and no support. Many directors made mistakes without realising — overpaying tax or triggering HMRC enquiries.

Modern filing software like Taxpipe actually saves you money by:

• Automatically calculating marginal relief (which many directors miss, costing them thousands)
• Catching common errors before submission
• Generating iXBRL-tagged accounts automatically
• Keeping records organised for future years

The switch from HMRC's free service isn't just necessary — it might be the best thing that's happened to your company's tax filing.

Next Steps

1. Check your deadline — know when your next CT600 is due
2. Sign up for Taxpipe — it takes 5 minutes to create an account
3. Use our corporation tax calculator to estimate what you'll owe
4. File with confidence — Taxpipe handles the technical complexity so you don't have to

The HMRC free service served its purpose, but it's time has come. The sooner you make the switch, the less stressful filing season will be.

Need help choosing the right CT600 filing solution? Compare our pricing or try our corporation tax calculator to see what you'll owe this year.