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Taxation (UK) · The scope of corporation tax

Corporation Tax Filing Deadlines, Payment Dates and Quarterly Instalments

Updated 11 October 2026 · Fact-checked

Corporation tax is normally paid 9 months and 1 day after the accounting period ends. The return is due 12 months after the period of account ends. Large companies (augmented profits above £1,500,000, adjusted for associates) pay by quarterly instalments instead. Late tax carries interest at 8.50%; overpaid tax earns 3.50%.

Understand Filing Deadlines, Payment Dates and Quarterly Instalments

A company works out its corporation tax for each accounting period. Two separate deadlines then apply: one for paying the tax and one for filing the return. Students often mix them up, so keep them apart.

The return (form CT600, filed online with the accounts) is due 12 months after the end of the period of account. The tax itself is due earlier, 9 months and 1 day after the end of the accounting period. So for a year ending 31 December 2025, the tax is due on 1 October 2026 and the return on 31 December 2026.

Larger companies do not pay in one sum. A company is large if its augmented profits exceed the profit threshold of £1,500,000. The threshold is divided by (number of associated companies + 1), and it is reduced pro rata for a short accounting period. A large company pays its tax in quarterly instalments based on its own estimate of the liability for the period. For a 12-month period, the first two instalments fall during the period and the last two fall after the period end.

A very large company has augmented profits above £20 million (also divided by the number of associated companies + 1, and time-apportioned for short periods). Its instalments fall earlier. This £20 million figure is not in the tax rates table supplied in the exam, so you must learn it.

There is also an exemption to learn. A company that is large but was not large in the previous 12-month period is not required to pay by instalments if its augmented profits do not exceed £10,000,000 (divided by associated companies + 1). Otherwise it pays by instalments. So a company that was large in the previous period pays by instalments whatever its profits. A company that was not large before, and whose augmented profits are above £10,000,000 (adjusted), also pays by instalments. The £10,000,000 figure is not supplied in the exam. Check this exemption before applying the instalment rules.

If tax is paid late, interest runs from the due date to the payment date. If tax is overpaid, HMRC pays interest to the company. The exam gives you the assumed rates: 8.50% on underpaid tax and 3.50% on overpaid tax. The official rate of 3.75% is a different rate, used for beneficial loans, and is not used here.

Key rules to remember

Return filing deadline
12 months after the end of the period of account
Late filing brings fixed and then tax-geared penalties, covered in the penalties topics.
Normal payment date
9 months and 1 day after the end of the accounting period
Applies to companies that are not large. Example: year to 31 December 2025 gives 1 October 2026.
Large company test
Augmented profits > £1,500,000 ÷ (associated companies + 1)
Time-apportion the threshold for a short accounting period. Use augmented profits, not just taxable total profits. A large company that was not large in the previous 12-month period is not required to pay by instalments if its augmented profits do not exceed £10,000,000 ÷ (associated companies + 1). Otherwise it pays by instalments.
Very large company test
Augmented profits > £20,000,000 ÷ (associated companies + 1)
Not in the tax rates table supplied in the exam, so learn it. Time-apportion for short periods.
Large company instalments (12-month period)
4 equal instalments, due 6 months and 13 days, 9 months and 13 days, 12 months and 13 days after the start, and 3 months and 14 days after the end of the period
For a year ending 31 December these are 14 July, 14 October, 14 January and 14 April. The first two fall in the period; the last two fall after the year end. Each is 25% of the estimated liability.
Very large company instalments (12-month period)
4 equal instalments due 2 months and 13 days, 5 months and 13 days, 8 months and 13 days and 11 months and 13 days after the start of the period
For a year ending 31 December these are 14 March, 14 June, 14 September and 14 December, all within the period.
Interest rates (supplied in exam)
Underpaid tax 8.50%; overpaid tax 3.50%
Interest = tax × rate × months ÷ 12, from the due date to the date of payment.

How to solve Filing Deadlines, Payment Dates and Quarterly Instalments questions

Use this order for any question on corporation tax deadlines, instalments or interest.

  1. 1Identify the accounting period: its start date, end date and length in months. Check for a short period.
  2. 2Compute the corporation tax liability for the period, using the correct rates and any marginal relief.
  3. 3Work out augmented profits (taxable total profits plus exempt dividends received from non-group companies) and count the associated companies.
  4. 4Divide the £1,500,000 threshold (and £20 million for very large) by the number of associated companies + 1, and time-apportion for a short period. Compare with augmented profits to decide: normal, large or very large.
  5. 5If the company is not large, state the payment date as 9 months and 1 day after the period end, and the return deadline as 12 months after the period of account ends.
  6. 6If the company is large or very large, divide the liability into equal instalments and attach the correct dates, counted from the start of the period (and from the end for the final large-company instalment).
  7. 7If any payment was late or early, calculate interest on the amount and the number of months, using 8.50% for underpaid tax and 3.50% for overpaid tax, and state which rate you used.

Quickest way: Date table by period end

When to use it: Use when the question asks only for dates or for a simple instalment schedule on a 12-month period.

  1. Write the period start and end dates on your scrap paper.
  2. Normal payment: add 9 months and 1 day to the end date. Return: add 12 months to the end date.
  3. Large instalments for a year to 31 December: 14 July, 14 October, then 14 January and 14 April of the next year. Shift the months to match the actual start date.
  4. Very large instalments: the 14th day of months 3, 6, 9 and 12 of the period.
  5. Check that the instalments add up to the full liability before moving on.

Common mistakes in Filing Deadlines, Payment Dates and Quarterly Instalments

  • Using 9 months and 1 day for a large company.

    It is the date you learn first, so you apply it to every company.

    Fix: Test the profit threshold first. Only a company that is not large pays in one sum after the period end.

  • Counting instalment dates from the period end instead of the start.

    Normal payment dates are counted from the end of the period.

    Fix: Count the first three large-company instalments from the start (6, 9 and 12 months plus 13 days). Only the last is counted from the end (3 months and 14 days). The third and fourth instalments fall after the period end: 14 January and 14 April for a December year end.

  • Ignoring associated companies when testing the threshold.

    The £1,500,000 figure appears in the rates table and looks like a fixed limit.

    Fix: Divide the threshold by the number of associated companies plus 1. With one associate, it is £750,000.

  • Using taxable total profits instead of augmented profits for the threshold.

    Taxable total profits are the figure you have just calculated.

    Fix: Add exempt dividends received from non-group companies to taxable total profits before comparing with the threshold.

  • Mixing up the interest rates or using the official rate.

    The table shows three rates close together: 3.75%, 8.50% and 3.50%.

    Fix: Underpaid tax: 8.50%. Overpaid tax: 3.50%. The 3.75% official rate is for beneficial loans.

  • Stating the filing deadline as 9 months after the period end.

    Confusing the return deadline with the payment deadline.

    Fix: The return is due 12 months after the end of the period of account. Write both dates separately in your answer.

Worked examples

Example 1

Bryn Ltd has no associated companies. For the 12 months ended 31 December 2025 it has taxable total profits of £400,000 and no dividend income. State the corporation tax payable, the payment date and the return deadline. If the tax is actually paid on 1 January 2027, calculate the interest.

Show the solution
  1. Taxable total profits of £400,000 exceed the upper limit of £250,000, so the main rate of 25% applies and there is no marginal relief.
  2. Corporation tax = £400,000 × 25% = £100,000.
  3. Augmented profits are £400,000, which is below the £1,500,000 threshold. Bryn Ltd is not large, so it pays in one sum.
  4. Payment date: 9 months and 1 day after 31 December 2025 = 1 October 2026.
  5. Return deadline: 12 months after 31 December 2025 = 31 December 2026.
  6. Payment on 1 January 2027 is 3 months late. Interest on underpaid tax is at 8.50%.
  7. Interest = £100,000 × 8.50% × 3 ÷ 12 = £2,125.

Answer: Corporation tax £100,000, due 1 October 2026. Return due 31 December 2026. Interest for late payment is £2,125.

Example 2

Kestrel Ltd has no associated companies and no dividend income. It was a large company in the previous 12-month period. For the 12 months ended 31 December 2025 its taxable total profits are £3,000,000. Explain how and when it pays its corporation tax.

Show the solution
  1. Taxable total profits of £3,000,000 exceed the upper limit, so the 25% main rate applies.
  2. Corporation tax = £3,000,000 × 25% = £750,000.
  3. Augmented profits of £3,000,000 exceed the £1,500,000 threshold, so the company is large. They are below £20 million, so it is not very large.
  4. Exemption check: the £10,000,000 exemption applies only to a company that was not large in the previous period. Kestrel was large in the previous period, so the exemption is unavailable (and its augmented profits of £3,000,000 are below £10,000,000 anyway). It must pay by instalments.
  5. A large company pays four equal instalments: £750,000 ÷ 4 = £187,500 each.
  6. Instalment dates for a year starting 1 January 2025: 14 July 2025 (6 months and 13 days after the start), 14 October 2025 (9 months and 13 days after the start), 14 January 2026 (12 months and 13 days after the start) and 14 April 2026 (3 months and 14 days after the end). The first two fall in the period and the last two after the period end.
  7. Check: 4 × £187,500 = £750,000.
  8. The return is still due 12 months after the period end, on 31 December 2026.

Answer: Kestrel Ltd is large and, having been large in the previous period, is not exempt. Its £750,000 liability is paid in four instalments of £187,500 on 14 July 2025, 14 October 2025, 14 January 2026 and 14 April 2026. The return is due by 31 December 2026.

Exam tips

  • Write down the threshold test as a short working. In a Section B objective test case, one slip here makes every later answer wrong.
  • Always check for associated companies in the scenario. They change the threshold and may also change the tax limits for marginal relief.
  • Show the instalment dates and amounts in a small table-style list in Section C, and add a total line to prove the instalments equal the liability.
  • State interest to the nearest £, show the rate, tax amount and number of months, and say whether tax was underpaid or overpaid.
  • Objective questions are all or nothing, so read whether the question asks for the payment date, the filing date, or the due date of a specific instalment.

Practice questions from The scope of corporation tax

Filing Deadlines, Payment Dates and Quarterly Instalments in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Filing Deadlines, Payment Dates and Quarterly Instalments: frequently asked questions

When is corporation tax due for a small company?

For a company that is not large, tax is due 9 months and 1 day after the end of the accounting period. For a year ended 31 December 2025, that is 1 October 2026. The return is due separately, 12 months after the period of account ends.

How do I know if a company has to pay quarterly instalments?

Compare its augmented profits with £1,500,000 divided by the number of associated companies plus 1. If augmented profits are higher, the company is large and pays by instalments. Time-apportion the threshold if the accounting period is shorter than 12 months.

What interest rate applies to late corporation tax in ACCA TX-UK?

The exam supplies an assumed rate of 8.50% on underpaid tax and 3.50% on overpaid tax. Interest runs from the due date to the date of payment. Multiply the tax by the rate and by months ÷ 12.

What is the difference between a large and a very large company?

A large company has augmented profits above £1,500,000 (adjusted for associates) and pays 6 months and 13 days after the start of the period, then quarterly, with the last two instalments falling after the year end. A very large company has profits above £20 million (adjusted) and pays earlier, with all four instalments falling within the period.