When is Corporation Tax due? Payment and filing dates explained

Corporation Tax has two separate dates: when the tax is paid, and when the Company Tax Return (CT600) is filed. They are not the same date, and the payment is actually due before the return.

The two dates in a sentence

• Pay Corporation Tax: 9 months and 1 day after the end of the accounting period (for companies with profits up to £1.5m).
• File the CT600: 12 months after the end of the accounting period.

So a company with a 31 March 2027 year end has to pay by 1 January 2028 and file by 31 March 2028. The payment is due even though the return is not.

Worked example

A company’s accounting period runs from 1 April 2026 to 31 March 2027. Taxable profits are £120,000 (illustrative).

Date	What is due
31 March 2027	End of accounting period.
1 January 2028	Corporation Tax payment due (9 months + 1 day).
31 March 2028	CT600 return filing deadline (12 months).

Interest runs on any Corporation Tax paid after the payment deadline, at HMRC’s late-payment interest rate.

Rates for financial year 2026

Corporation Tax rates are set by financial year, which runs 1 April to 31 March. For financial year 2026 (1 April 2026 to 31 March 2027):

• Small profits rate: 19% for taxable profits up to £50,000.
• Main rate: 25% for taxable profits above £250,000.
• Marginal relief applies between £50,000 and £250,000, giving an effective rate that rises gradually from 19% to 25%.

The £50,000 and £250,000 limits are reduced where a company has associated companies or a short accounting period. A qualified accountant can confirm how associated-companies rules apply.

How marginal relief works, roughly

Marginal relief is calculated using a fraction set by HMRC (currently 3/200). In broad terms, every £1 of profit between £50,000 and £250,000 is taxed at 26.5%, so the average effective rate rises smoothly from 19% at £50,000 to 25% at £250,000. HMRC’s online calculator does the detail.

Quarterly instalments for larger companies

Companies with taxable profits over £1.5 million pay in quarterly instalments rather than a single payment. The thresholds are divided by the number of related 51% group companies plus one.

Profit level	Instalment rule (12-month accounting period)
Over £1.5m – £20m	Four quarterly instalments: months 7, 10, 13 and 16 from the start of the accounting period.
Over £20m (very large)	Four quarterly instalments, each three months earlier: months 3, 6, 9 and 12 from the start of the accounting period.

For companies that have just crossed the £1.5m threshold, there is a one-year grace period if profits were under £1.5m in the previous year and under £10m in the current year. HMRC’s manuals are the authoritative source.

Late filing penalties

Separate penalties apply for a late CT600. HMRC’s standard penalty tiers for returns with a filing date on or after 1 April 2026 are set out below. These are flat penalties and apply even if there is no Corporation Tax to pay.

How late	Fixed penalty (from 1 April 2026)
1 day late	£200
3 months late	£200 additional
6 months late	£400 additional
12 months late	£400 additional

In addition, where a return is filed 6 months late, HMRC estimates the tax and adds a tax-geared penalty of 10% of the unpaid tax; at 12 months late this rises to 20%.

Common edge cases

• Long accounting period. A period longer than 12 months is split into two accounting periods for Corporation Tax: the first 12 months, then the balance. Each has its own payment and filing dates.
• Short accounting period. Common in a company’s first year or when the year-end is changed. The small-profits and marginal-relief thresholds are reduced in proportion.
• Dormant company. A company that has told HMRC it is dormant for Corporation Tax does not need to file a CT600 for the dormant period.

What tends to go wrong

The most common issue is confusion between the two dates. Owner-directors sometimes assume they can pay once the CT600 is filed, which is three months after the payment deadline. Interest will already have run on the unpaid tax. The second common issue is cash. Corporation Tax is a once-a-year outflow for smaller companies and can be large relative to a single month’s trading. Setting aside the estimated liability each month, or holding it in a separate reserve account, avoids a surprise.

Nella produces a running VAT, PAYE and Companies House date timeline from Xero, QuickBooks, Sage or FreeAgent data, including the Corporation Tax payment date for the current accounting period. Decisions on provision and timing sit with a qualified accountant.

Nella provides financial information and education, not accounting or tax advice.

Work it out: Try the Corporation Tax calculator (FY2026) — it runs in your browser and states the rule it applies.

Sources

• GOV.UK u2014 Pay your Corporation Tax bill
• GOV.UK u2014 Company Tax Returns
• GOV.UK u2014 Corporation Tax rates
• GOV.UK u2014 Marginal Relief for Corporation Tax

Nella provides financial information and education, not accounting or tax advice. Nella shows you the numbers. When a question needs professional judgement, such as a filing or a tax decision, Nella says so and points you to a qualified accountant.