UK Corporation Tax is paid 9 months and 1 day after the company''s accounting period ends — earlier than the filing deadline of 12 months. Large companies (taxable profits over £1.5m) pay in quarterly instalments starting 6 months and 14 days into the accounting period. Missing the payment date triggers interest at the HMRC rate plus penalties.
This is the most-confused tax deadline for UK SME directors. Payment first, return later — but most directors assume "tax is due when the return is due". It''s not.
The two distinct deadlines
For a typical UK limited company with a 12-month accounting period:
Payment of Corporation Tax
- Due: 9 months and 1 day after the end of the accounting period.
- So for accounts ending 31 March 2026: tax due 1 January 2027.
Filing of the Corporation Tax return (CT600)
- Due: 12 months after the end of the accounting period.
- So for accounts ending 31 March 2026: CT600 due 31 March 2027.
The 3-month gap exists because HMRC wants the cash before the paperwork. Smaller companies (with profits under £1.5m, see below) pay the tax in one lump sum 9 months and 1 day after period end. Larger companies pay in quarterly instalments.
The "small companies" payment rule
Standard for most UK SMEs (taxable profits up to £1.5 million):
- Pay the full Corporation Tax in a single payment.
- Due 9 months and 1 day after the accounting period end.
For a 31 March year-end:
- Period ends: 31 March.
- Payment due: 1 January (next year).
- CT600 due: 31 March (next year).
Quarterly instalments for large companies
Companies with taxable profits over £1.5 million pay in quarterly instalments. The £1.5m threshold is divided by the number of associated companies — so a small company in a 3-company group has effective threshold £500K.
Quarterly instalment dates (for a 12-month accounting period ending 31 March):
- Instalment 1: 14 October (month 6 + 14 days of the accounting period).
- Instalment 2: 14 January.
- Instalment 3: 14 April (post period end).
- Instalment 4: 14 July.
Each instalment is roughly 25% of the expected liability for the period, based on best estimates at each due date.
If estimates change during the year, payments are adjusted. Over- or underpayment is reconciled at year-end via the CT600.
Very large companies (profits over £20m)
A separate accelerated payment schedule:
- Instalment 1: 14 February (month 5 of the period).
- Instalment 2: 14 May.
- Instalment 3: 14 August.
- Instalment 4: 14 November.
For a 31 March year-end, the first instalment falls 5 months into the period — before the period has even ended. This is genuinely demanding cash flow planning.
How to actually pay
Methods accepted by HMRC
- Bank transfer (Faster Payment): instant clearing. Pay to HMRC''s Cumbernauld or Shipley accounts (check which applies to your reference) with the company''s Corporation Tax reference.
- CHAPS: same-day clearing for larger payments.
- BACS: 3 working days. Don''t cut this fine.
- Direct Debit: only available for companies set up for it in advance.
What you need
- The company''s 17-character Corporation Tax payment reference (NOT the UTR — it''s longer and includes the accounting period reference).
- The amount.
The 17-character reference is unique per accounting period. Get it wrong and HMRC may allocate the payment to the wrong period.
Interest on late payment
HMRC charges interest on Corporation Tax paid after the due date. As of 2026, this is base rate + 2.5% — currently around 7.75%.
Interest runs from the original due date until paid in full. It accrues automatically; no judicial action required.
Conversely, HMRC pays interest on Corporation Tax paid early. The repayment rate is currently around 4%. For companies with steady cash, paying Corporation Tax early can earn meaningfully more than typical business bank account rates.
Penalties for non-payment
Unlike Self Assessment, there are no separate "5% per month" surcharges on Corporation Tax. Interest is the main penalty for late payment.
However, persistent late payment damages the company''s relationship with HMRC and can:
- Trigger increased scrutiny of the company.
- Impact future Time to Pay arrangements.
- Lead to enforcement action (winding-up petitions for serious cases).
Filing the CT600 — separate deadlines
The CT600 itself is due 12 months after the period end. Filing it is a separate obligation from paying the tax.
Late filing penalties:
- 1 day late: £100.
- 3 months late: another £100.
- 6 months late: HMRC estimates the liability and charges accordingly, plus 10% of unpaid tax.
- 12 months late: another 10% of unpaid tax.
After 2 consecutive late filings, the £100 escalates to £500.
Common mistakes
Confusing payment and filing dates
"My CT600 is due 31 March 2027 so I have until then to pay." No — payment was due 1 January 2027. The 3-month gap is for the paperwork only.
Wrong payment reference
Allocating the payment to the wrong accounting period because the 17-character reference is wrong. HMRC may sit on the payment in suspense until clarified.
Forgetting quarterly instalments
A growing company crosses the £1.5m threshold and forgets to switch to quarterly instalments. Underpayment plus interest follows.
Late payment before late filing
Paying late and then expecting HMRC to be lenient because "we''re filing on time" — they're not the same obligation.
What to do this quarter
- Mark your Corporation Tax payment date in the calendar with 30-day and 7-day reminders.
- Note: payment date is 9 months and 1 day after period end, NOT 12 months.
- Forecast the tax bill 2-3 months before payment date so you''re not surprised.
- Set up direct debit with HMRC for Corporation Tax if you''re comfortable with auto-payment.
- If you''re approaching the £1.5m taxable profit threshold (divided by associated companies), plan for the move to quarterly instalments.