HMRC's Free Filing Service Has Closed
HMRC's free online CT600 filing service closed on 31 March 2026. Since that date, every UK limited company must use commercial software to file corporation tax returns.
If you've been filing directly through HMRC's website, this guide walks you through your options and how to switch to online filing software with minimal disruption.
What's Actually Changing?
HMRC isn't changing the CT600 form itself — the same boxes, the same calculations, the same deadlines. What's changing is the method of submission. Instead of typing numbers into HMRC's website, you'll submit your return through software that generates the XML file HMRC requires.
The key dates:
- 31 March 2026: HMRC free filing service closed
- Your normal deadline: 12 months after your accounting period ends
- Payment deadline: 9 months and 1 day after your accounting period ends
Step 1: Gather Your Information
Before you start, you'll need:
- Company details: Company Registration Number (CRN) and Unique Taxpayer Reference (UTR)
- Accounting period: The start and end dates of the period you're filing for
- Financial figures: Turnover, cost of sales, expenses, and profit/loss
- Capital allowances: Details of any plant, machinery, or equipment purchases
- Previous losses: Any trading losses carried forward from earlier periods
If you've filed before through HMRC's service, you'll be familiar with most of this. The numbers are the same — it's just the filing method that changes.
Step 2: Choose Your Software
You need HMRC-recognised software that can:
- Generate CT600 XML in the format HMRC requires
- Create iXBRL accounts and tax computations
- Submit directly to HMRC via their Transaction Engine API
Taxpipe handles all of this for £59 per filing — no subscription, no accountant fees.
When choosing software, check:
- ✅ HMRC-recognised (listed on GOV.UK)
- ✅ Handles iXBRL generation (not just the CT600 form)
- ✅ Supports your company type (micro-entity, small, dormant)
- ✅ Clear pricing with no hidden fees
Step 3: Enter Your CT600 Data
The CT600 form has over 200 boxes, but most companies only need to fill in a fraction of them. A typical micro-entity contractor filing looks like this:
Company Information (Boxes 1-50)
- Company name, CRN, UTR
- Accounting period dates
- Company type
Turnover and Income (Boxes 145-210)
- Total turnover (Box 145)
- Trading profits (Box 155)
Tax Calculation (Boxes 315-440)
- Profits chargeable to corporation tax
- Corporation tax rate applied
- Tax due
Declaration
- Director's name and confirmation
Most software — including Taxpipe's calculator — will auto-calculate the tax boxes for you based on your income and expenses.
Step 4: Prepare Your Accounts
Your CT600 submission must include:
- Statutory accounts in iXBRL format
- Tax computations in iXBRL format
iXBRL (Inline eXtensible Business Reporting Language) is a tagged format that allows HMRC to process your accounts digitally. You don't need to understand iXBRL — your software generates it.
For micro-entity companies, the accounts are straightforward: a balance sheet, a profit and loss summary, and some notes. The size thresholds depend on when your financial year begins: for accounting periods starting before 6 April 2025, the limits are turnover ≤ £632,000 and balance sheet ≤ £316,000; for periods starting on or after 6 April 2025, the limits rise to turnover ≤ £1,000,000 and balance sheet ≤ £500,000.
Step 5: Review and Submit
Before submitting:
- Double-check your accounting period dates (HMRC is strict about this)
- Verify your UTR and CRN are correct
- Review the tax calculation — does the tax amount look right for your profit level?
- Check you've included all income and claimed all allowable deductions
Once you're satisfied, submit through your software. You'll receive a confirmation from HMRC with a correlation ID and timestamp.
Step 6: Pay Your Corporation Tax
Filing and paying are separate. After filing your return, pay your corporation tax by the payment deadline (9 months and 1 day after your accounting period ends).
Payment methods:
- Online banking (same day or next day)
- BACS (3 working days)
- CHAPS (same day)
- Direct Debit (if set up in advance)
Your payment reference is a 17-character code shown on your HMRC payslip or in your business tax account: your 10-digit UTR, followed by 'A001', a 2-digit accounting period number, and 'A' (for example, 1234567890A00101A). Always use the reference shown in your HMRC online account — the period number increments with each return and must match exactly.
Common Questions
Do I need an accountant?
No. If your company is straightforward — a single director/shareholder with simple income and expenses — you can file yourself using software like Taxpipe.
What if I miss the deadline?
For returns with a filing date on or after 1 April 2026, HMRC charges £200 for a return filed up to 3 months late, with a further £200 at 3 months (£400 total). From 6 months, a tax-geared penalty of 10% of any unpaid tax is added, with a further 10% at 12 months. Don't miss it.
Can I still file for free?
Since March 2026, there is no free option from HMRC. Commercial software prices range from £59 (Taxpipe) to several hundred pounds for full-service accountancy.
What if my company is dormant?
If your company is dormant and has notified HMRC, you only need to file a CT600 if HMRC sends you a notice to deliver — you do not file automatically. If HMRC does issue a notice, the return is straightforward — most boxes are zero. Taxpipe handles dormant filings with a streamlined process.
Getting Started
The transition from HMRC's free service to commercial software doesn't have to be painful. With the right tool, filing takes about 30 minutes.
Try Taxpipe's free calculator to see your estimated corporation tax, then file your return for £59.