Corporation Tax is due 9 months and 1 day after the end of your company’s accounting period, while your CT600 Company Tax Return must be filed within 12 months of that date. The payment deadline comes first, about three months before filing. Companies with taxable profits over £1.5 million pay earlier, in quarterly instalments.
Corporation Tax Deadlines at a Glance
Every Corporation Tax deadline is counted from the end of your accounting period (usually your company’s financial year end):
| Obligation | Deadline |
|---|---|
| Register for Corporation Tax | Within 3 months of starting to do business |
| Pay your Corporation Tax | 9 months and 1 day after the accounting period ends |
| File your CT600 Company Tax Return | 12 months after the accounting period ends |
| Large companies (profits over £1.5m) | Four quarterly instalments during the year (see below) |
When Is Corporation Tax Due? The 9 Months and 1 Day Rule
For most small and medium companies, Corporation Tax must be paid 9 months and 1 day after the end of the accounting period. There is no payslip in the post — you pay HMRC directly. Two quick examples:
- Year end 31 March 2026 → payment due 1 January 2027.
- Year end 31 December 2025 → payment due 1 October 2026.
This is the deadline that catches most directors out, because it falls three months before the return itself is due. You have to work out and pay the tax before you formally file. Getting your annual accounts finalised early is the simplest way to know your bill in good time.
When Is the CT600 Filing Deadline?
Your CT600 Company Tax Return must be filed online within 12 months of the end of your accounting period. For a 31 March 2026 year end, that means filing by 31 March 2027 — three months after the payment deadline. The return must be submitted in the required iXBRL format, with your accounts and tax computations attached. You must file even if your company made a loss or has no tax to pay — HMRC still expects the return, and a “nil” return keeps you compliant. Our Corporation Tax and CT600 service handles the whole submission for you.
Note: your accounts also go to Companies House on a separate deadline. A newly formed company’s first period can run up to 18 months for Companies House, but a Corporation Tax accounting period can’t exceed 12 months — so a long first period is split into two CT600 returns.
Corporation Tax Rates for 2025/26 and 2026/27
How much you owe depends on your taxable profits. The rates are unchanged for both years:
| Taxable Profits | Rate |
|---|---|
| Up to £50,000 | 19% (small profits rate) |
| £50,001 – £250,000 | Marginal relief (effective rate around 26.5% on profits in the band) |
| Over £250,000 | 25% (main rate) |
The £50,000 and £250,000 thresholds are divided by the number of associated companies and pro-rated for accounting periods shorter than 12 months. Marginal relief tapers the rate between the two limits, so it’s worth claiming if your profits fall in that range.
Large Companies: Quarterly Instalment Payments
If your taxable profits exceed £1.5 million, you must pay Corporation Tax in four quarterly instalments (QIPs) rather than a single payment. For a 12-month period, the instalments fall in months 7, 10, 13, and 16 counted from the start of the period — so the first two are due before the year has even ended, based on your own estimate. For example, a large company with a 31 March 2026 year end pays on 14 October 2025, 14 January 2026, 14 April 2026, and 14 July 2026.
Very large companies, with profits over £20 million, pay even earlier, in months 3, 6, 9, and 12. Both the £1.5m and £20m thresholds are divided by the number of associated companies, so groups can fall into the instalment regime at much lower profits. If your profits are under £1.5 million, none of this applies — you make one payment, 9 months and 1 day after your year end.
How to Pay Your Corporation Tax
You pay HMRC directly online using your 17-character Corporation Tax payment reference for the specific accounting period. This reference changes each period, so always use the correct one — you’ll find it in your HMRC online account or on your payment reminder. Allow enough time for your chosen method to clear:
| Payment Method | Time to Reach HMRC |
|---|---|
| Online/telephone banking (Faster Payments) | Same or next day |
| CHAPS | Same or next working day |
| Debit or corporate credit card online | Same or next day |
| Bacs / existing Direct Debit | About 3 working days |
| New Direct Debit (first time) | About 5 working days |
| At your bank or building society | About 3 working days |
There’s no penalty for paying early — and if you overpay or pay ahead of the deadline, HMRC pays you a small amount of credit interest.
What Happens If You Miss a Corporation Tax Deadline?
Late filing and late payment are penalised separately. Miss the CT600 filing deadline and HMRC charges automatic penalties that escalate over time:
| How Late (Filing) | Penalty |
|---|---|
| 1 day late | £100 |
| 3 months late | A further £100 |
| 6 months late | HMRC estimates your bill and adds 10% of the unpaid tax |
| 12 months late | Another 10% of the unpaid tax |
File late three times in a row and the £100 penalties rise to £500 each. On the payment side, HMRC charges daily interest on any Corporation Tax paid late, running from the payment deadline at the Bank of England base rate plus 4% (check GOV.UK for the current rate). Interest and penalties are separate, so a late, unpaid return can cost far more than the tax itself.
How to Avoid Corporation Tax Penalties
- Know your two dates. Payment at 9 months and 1 day; filing at 12 months. Diarise both from your year end.
- Finalise your accounts early. Strong bookkeeping means you know your bill months before it’s due.
- Budget for the bill. Set aside tax as profits come in, so payment day isn’t a shock.
- Use the right payment reference. The wrong reference can leave your payment unallocated and appear “late.”
- Check if instalments apply. Growing companies and groups can cross the £1.5m threshold sooner than expected.
- Let an accountant track it. We watch every deadline, file your CT600 accurately, and claim the reliefs you’re due.
Corporation Tax and Your Other Company Deadlines
Corporation Tax rarely sits on its own. As a director you’ll likely also juggle a Self Assessment tax return, VAT returns under Making Tax Digital, payroll and RTI submissions, and your statutory annual accounts at Companies House. Just formed your company? Our company formation service gets your Corporation Tax registration set up correctly from day one.
Get Help With Your Corporation Tax
ATB Solutions is a Birmingham-based accountancy practice supporting limited companies across the West Midlands. We prepare and file your Corporation Tax return, track every deadline, and plan your salary and dividends to keep the bill efficient — all for a fixed monthly fee. Download our Limited Company Summary Sheet to get organised before year end, see why clients choose us, or book a free consultation today.
Frequently Asked Questions
When is Corporation Tax due?
Corporation Tax is due 9 months and 1 day after the end of your company’s accounting period. For a 31 March 2026 year end, payment is due by 1 January 2027. Companies with profits over £1.5 million pay in quarterly instalments instead.
Is the Corporation Tax payment deadline the same as the CT600 filing deadline?
No. Payment is due 9 months and 1 day after the accounting period ends, while the CT600 return is due 12 months after. The payment deadline falls about three months before the filing deadline.
What is the Corporation Tax rate for 2025/26 and 2026/27?
Profits up to £50,000 are taxed at 19%, profits over £250,000 at 25%, and profits in between qualify for marginal relief, giving an effective rate of around 26.5% on the profits within that band.
Do I have to file a CT600 if my company made no profit?
Yes. An active company must file a CT600 within 12 months of its accounting period end even if it made a loss or has no tax to pay. Filing a nil return keeps you compliant and avoids penalties.
What are the penalties for filing my Corporation Tax return late?
You get a £100 penalty at 1 day late, a further £100 at 3 months, then 10% of the unpaid tax at 6 months and another 10% at 12 months. Filing late three years running raises the £100 penalties to £500 each, and interest is charged on any late payment.
How do I pay Corporation Tax to HMRC?
You pay HMRC directly online using your 17-character Corporation Tax payment reference for that accounting period. Faster Payments, CHAPS, and card payments usually clear the same or next working day, while Bacs and Direct Debit take longer, so allow enough time.
