File CT600 After HMRC Free Service Closes (2026)

Filing Your CT600 From April 2026: Everything You Need to Know

From 1 April 2026, the only way to file a CT600 Corporation Tax return with HMRC is through approved third-party software. If you've always used HMRC's free online service, this guide walks you through the entire process of switching — from choosing software to submitting your return.

No accountancy jargon, no assumptions about what you already know. Just clear steps.

What Changed and Why

HMRC's free Corporation Tax filing service officially closed on 31 March 2026. This was part of HMRC's long-term strategy to shift tax administration to commercial software providers, in line with the Making Tax Digital programme.

The practical impact is straightforward: you now need to use HMRC-recognised software to prepare, calculate, and submit your CT600.

Step-by-Step: Filing Your CT600 With Commercial Software

Step 1: Choose Your Software

Your software needs to be on HMRC's list of recognised CT600 filing software. Key features to look for:

• CT600 preparation and submission — obviously
• iXBRL accounts generation — your company accounts must be submitted in iXBRL format alongside the CT600
• Auto-calculation of tax — including marginal relief for profits between £50,000 and £250,000
• Validation and error checking — catches mistakes before HMRC sees them
• Reasonable pricing — you're replacing a free service, so cost matters

Taxpipe was built specifically for directors who previously used HMRC's free service. It handles the entire process — CT600 preparation, tax calculation, iXBRL accounts, and HMRC submission — in one place. No accounting knowledge required. See our pricing for details.

Step 2: Register and Set Up Your Company

Once you've chosen your software:

1. Create an account with the software provider
2. Add your company details — company name, Companies House number, UTR
3. Enter your accounting period dates — the start and end dates of the period you're filing for
4. Connect to HMRC — you'll need your Government Gateway user ID and password

Most software will pull some company details from Companies House automatically when you enter your company number.

Step 3: Prepare Your Financial Information

Before you start entering data, have these ready:

Income:

• Total turnover (sales/revenue) for the period
• Bank interest received
• Any other income (rental, investment, etc.)

Expenses:

• All allowable business expenses
• Depreciation figures (you'll need these for capital allowances)
• Director's salary and employer's NIC
• Pension contributions
• Professional fees, subscriptions, insurance
• Office costs, travel, marketing

Assets:

• Equipment, vehicles, or machinery purchased during the period
• Any assets sold or disposed of

Other:

• Director's loan account balance at period end
• Dividends paid during the period
• Any losses brought forward from previous periods

Step 4: Enter Your Data

With Taxpipe, this works as a guided questionnaire. You answer questions in plain English, and the software maps your answers to the correct CT600 boxes. For example:

• "What was your company's total turnover?" → maps to Box 145
• "Did you purchase any equipment?" → triggers capital allowances calculation
• "What was the total amount of director's salary?" → included in trading expenses

Other software may require you to fill in CT600 boxes directly, which is more complex.

Step 5: Review the Calculations

Good software will show you:

• Total taxable profits — your income minus allowable expenses and reliefs
• Corporation tax rate applied — 19% for profits up to £50,000, 25% for profits over £250,000, or the marginal rate in between
• Marginal relief (if applicable) — this is the relief that reduces your effective rate if profits fall between £50,000 and £250,000
• Tax due — the final amount you owe HMRC

Use our free corporation tax calculator to cross-check the figures before filing.

Step 6: Generate and Review Your Accounts

Your CT600 submission must include iXBRL-tagged company accounts. This is the digital format HMRC requires.

If you're using Taxpipe, your iXBRL accounts are generated automatically from the data you've entered. You'll see a preview of your:

• Profit and loss account
• Balance sheet
• Notes to the accounts

Review these carefully. Common things to check:

• Does the turnover figure match your records?
• Are director's costs correctly categorised?
• Does the balance sheet balance? (it should — software handles this)
• Are brought-forward figures correct from last year?

Step 7: Submit to HMRC

Once you're satisfied everything is correct:

1. Run the validation check — software will flag any errors or missing fields
2. Fix any issues — common ones include missing UTR, incorrect period dates, or missing accounts data
3. Authorise the submission — enter your Government Gateway credentials
4. Submit — the software sends your CT600 and iXBRL accounts to HMRC electronically
5. Save the confirmation — you'll receive an HMRC submission receipt with a correlation ID. Keep this safe.

Step 8: Pay Your Corporation Tax

Filing and paying are separate. After submitting your CT600, you still need to pay any corporation tax owed. The payment deadline is 9 months and 1 day after your accounting period ends — which may be before your CT600 filing deadline.

Payment methods include:

• Direct bank transfer (same-day or Faster Payments)
• Direct Debit (set up through your HMRC account)
• Corporate credit/debit card (fee applies)

Your payment reference is your company's UTR followed by the accounting period end date.

Tips for a Smooth Transition

Don't wait until the deadline

Your CT600 is due 12 months after your accounting period ends. But starting early means you can catch problems, find missing receipts, and avoid the deadline rush.

Keep your Government Gateway credentials handy

You'll need these every time you file. Store them securely — if you lose them, recovering access from HMRC can take weeks.

Use the software's built-in checks

Modern filing software catches errors that HMRC's free service never did. Pay attention to validation warnings — they're there to protect you.

Save copies of everything

Download PDF copies of your submitted CT600, iXBRL accounts, and HMRC confirmation. Store them for at least 6 years (HMRC's record-keeping requirement).

Consider marginal relief

If your company's profits are between £50,000 and £250,000, you're entitled to marginal relief that reduces your effective tax rate below 25%. Good software calculates this automatically, but it's worth understanding — our calculator can show you exactly how it works.

What If You Haven't Filed Previous Returns?

If you have outstanding CT600 returns from periods when the free service was available, you still need to file them — and you'll now need to use commercial software to do so.

Late filing penalties accumulate:

Plus HMRC charges daily interest on any unpaid tax from the payment deadline.

If you're behind, file as soon as possible. The penalties keep growing. Taxpipe can help you file outstanding returns quickly.

Frequently Asked Questions

Can I file a CT600 for free anywhere?

HMRC no longer offers free filing. Some software may offer limited free tiers, but for a reliable, full-featured solution, expect to pay a modest fee. Taxpipe's pricing is designed to be accessible for small companies — check our plans.

Do I need to file accounts separately with Companies House?

Yes. Your CT600 goes to HMRC. Your annual accounts go to Companies House separately. Some software can help with both, but they are distinct filings with different deadlines.

What if my company is dormant?

You still need to file a CT600 nil return. Commercial software handles this — it takes about 15 minutes with Taxpipe.

Can my accountant still file for me?

Absolutely. Accountants use commercial software (they always have). If you use an accountant, this change doesn't affect you.

Making the Switch: It's Easier Than You Think

The move from HMRC's free service to commercial software sounds daunting, but for most small companies, the entire process takes under an hour. The software does the heavy lifting — calculating tax, generating iXBRL, and handling the HMRC submission.

And honestly? Your filing experience will be better than it was with the free service. Better error checking, automatic calculations, and proper support if something goes wrong.

Ready to file your CT600? Get started with Taxpipe — answer simple questions, and we handle the rest. Check our pricing or estimate your tax with our calculator.