Corporation Tax Deadlines: pay, file and keep records in the right order

Three deadlines, three jobs

A limited company normally has to prepare annual accounts, file accounts with Companies House, calculate and pay Corporation Tax, and file a Company Tax Return with HMRC. Each job uses related records, but the relevant deadlines are not one date. The most common avoidable mistake is remembering the annual-accounts deadline and assuming it covers the tax return or payment.

GOV.UK’s current limited-company overview gives a useful headline calendar. It says annual accounts are normally filed with Companies House nine months after the end of the financial year; Corporation Tax is paid or HMRC is told no tax is due nine months and one day after the Corporation Tax accounting period ends; and the Company Tax Return is filed twelve months after the Corporation Tax accounting period ends. A company’s first year, a changed accounting reference date, dormancy, very high profits or unusual circumstances can change what needs checking.

The safe working rule is not to memorise a generic month. Record the actual period-end dates on the company calendar, then work back from the payment date. Payment generally comes before the Company Tax Return filing deadline, so waiting to finalise records until the return deadline can create a cash and compliance problem.

The first year can split the tax periods

A newly incorporated company needs an extra first-year check. Companies House annual accounts follow the company’s financial year, but a Corporation Tax accounting period cannot simply be assumed to match a long first set of accounts. HMRC’s payment guidance says a company may have two Corporation Tax accounting periods in the year it is set up, and the Company Tax Return deadline applies to each accounting period.

Build the first-year timeline from the incorporation date, the company’s accounting reference date, the date it started trading or became liable to Corporation Tax, and any HMRC notice to deliver a return. Check each short or split Corporation Tax period separately for its period end, payment date and return deadline. Then keep the Companies House first-accounts deadline separate: GOV.UK currently states that first accounts are normally due 21 months after incorporation.

The practical control is to ask the accountant or HMRC which accounting periods exist before calculating the reserve. A first-year calendar that contains only the Companies House accounts date can miss an earlier Corporation Tax payment or a second Company Tax Return.

• Record incorporation and trading dates, the accounting reference date and every Corporation Tax accounting-period end.
• Create one payment and one Company Tax Return entry for each Corporation Tax accounting period shown by HMRC.
• Create a separate first-accounts entry for Companies House and do not use it as a proxy for the tax-payment date.

What Corporation Tax is calculated on

Corporation Tax is paid by companies and certain other organisations on taxable profits in an accounting period. HMRC’s overview identifies trading profits, investment income and chargeable gains as possible components. The Corporation Tax calculation is not simply the bottom line of management accounts and it is not a bill that arrives automatically for you to approve.

This is why clean records matter. GOV.UK says company accounting records must include money received and spent, assets, debts owed and owing, stock where relevant, goods bought and sold, and the documents and calculations needed to prepare annual accounts and the Company Tax Return. Keeping personal and company transactions separate is part of making those records dependable.

Do not publish or rely on a generic Corporation Tax percentage as a personal liability. Rates, reliefs, associated-company rules and adjustments can affect the calculation. Use the current HMRC sources and your accountant or tax adviser for the company’s actual position.

The 2026 software change matters

HMRC’s joint ‘File your accounts and Company Tax Return’ online service closed on 31 March 2026. Its current guidance says that from 1 April 2026 a company should use commercial software to file annual accounts and Company Tax Returns with HMRC, unless it has a reasonable excuse or is filing in Welsh and can use the limited paper route.

This is not a reason to buy the first package that advertises a filing feature. Confirm the software can produce the elements your company needs, including the CT600, Corporation Tax computation and accounts where relevant. Agree with the accountant who prepares the figures, who reviews the return, who files it, and where the submitted copy and proof of payment are stored.

Run the process before the payment deadline. An unfiled return may still be weeks away while a tax payment needs cash in the bank now. The audit trail should show the period end, working papers, approval, payment reference, payment date, submitted return and Companies House filing evidence.

Paying, filing and late consequences are separate controls

The Corporation Tax payment date arrives before the Company Tax Return filing date for an ordinary accounting period. That means a company may need to estimate and reserve for the liability before the final return is filed; filing later does not move the earlier payment deadline. The accounts and tax computation should explain how the amount was calculated and what remains uncertain.

HMRC says a Company Tax Return can attract a late-filing penalty even where the company has no tax to pay, while late Corporation Tax payment can lead to interest. Do not wait for a reminder or assume that a nil result removes the filing duty. If a deadline has been missed or a payment may not be made on time, keep evidence of the position and contact HMRC and a qualified adviser promptly.

Payment method also affects the operational deadline: HMRC lists different clearing times for Faster Payments, CHAPS, card, Direct Debit and Bacs. Check the current payment page and allow enough time for the chosen method to reach HMRC, especially before a weekend or bank holiday.

• Payment control: reserve the expected amount and confirm the 17-character payment reference for the relevant period.
• Filing control: prepare the CT600, computation and accounts in the appropriate software and retain submission evidence.
• Exception control: record any late filing, late payment, rejected return or inability to pay and escalate it rather than hiding it in the calendar.

Build a company tax calendar that survives a busy year

Start with the accounting-period end and the financial-year end. They are often aligned, but the calendar should identify both rather than assume. Add the normal payment, Company Tax Return and Companies House accounts dates. Then add internal dates: books closed, bank reconciled, payroll/VAT completed, accountant review, director approval, payment authority and filing check.

Most companies with taxable profits up to £1.5 million use the nine-month-and-one-day payment rule. HMRC says larger-profit companies pay in instalments, so a high-growth company should check the current rules rather than using the ordinary deadline. If a payment date falls on a weekend or bank holiday, HMRC’s payment guidance says to ensure the money reaches it on the preceding working day unless paying by Faster Payments through online or telephone banking.

A reserve is most useful when it is connected to this calendar and a rolling cash forecast. The target is not a reassuring bank balance; it is a known amount held for a known obligation and date. If the company cannot pay a bill, check the current HMRC help route and obtain advice early rather than quietly delaying the issue.

What to do, in order

1. 1

   Confirm the company’s period-end dates

   Record the financial-year and Corporation Tax accounting-period ends; do not assume they are always identical.

2. 2

   Enter each external deadline separately

   Add the Companies House accounts date, HMRC payment date and Company Tax Return date with clear labels.

3. 3

   Set the internal close timetable

   Schedule bookkeeping, reconciliation, records review, adviser queries, director approval, payment and submission before the external dates.

4. 4

   Check the filing method

   For 2026 onward, confirm appropriate commercial software and responsibilities for the CT600, computation, accounts and Companies House filing.

5. 5

   Protect and reconcile the tax reserve

   Connect the expected payment to the cash forecast and retain proof of payment and submission with the period records; do not wait for the return deadline to reserve cash.

6. 6

   Run a first-year and exception review

   Check whether the first year contains more than one Corporation Tax period, whether a return has been rejected or missed, and whether the chosen payment method will clear before the deadline.