Filing the Company Tax Return does not pay the tax. Payment is a separate step, made directly to HMRC, and for most companies it is due three months before the return. This page explains when the tax is due, where Tax Optimiser shows the figure and the date, and how to keep a record of what has been paid.
When the tax is due
For most companies, Corporation Tax is due nine months and one day after the end of the accounting period. The return itself is due 12 months after the end of the period.
| Accounting period ends | Pay by | File the return by |
|---|---|---|
| 31 March 2025 | 1 January 2026 | 31 March 2026 |
| 30 June 2025 | 1 April 2026 | 30 June 2026 |
| 31 December 2025 | 1 October 2026 | 31 December 2026 |
So the tax usually has to be worked out, and paid, before the return is sent. If the figures are not final by the due date, pay an estimate: interest runs only on what turns out to be underpaid. The free Corporation Tax deadlines calculator gives both dates for any year end.
Where Tax Optimiser shows the amount and the date
The amount is the Corp tax payable figure at the top of Corp Tax Calculations. The computation document adds the due date on its Corporation Tax Payments page, which you can open from Computation Document in Corp Tax Calculations and which is part of what is sent to HMRC.
The figure to pay is the total after everything on the return: tax on the profits, plus any charge on loans to participators, less reliefs, tax already deducted and credits. If the result is a repayment, see CT600 repayments.
Periods longer than 12 months
A period of account longer than 12 months is two accounting periods for tax, with two returns and two payment dates. Each amount is due nine months and one day after the end of its own accounting period, so the first falls due well before the accounts are finished.
For accounts running from 1 January 2025 to 31 March 2026, the tax for the 12 months to 31 December 2025 is due on 1 October 2026, and the tax for the three months to 31 March 2026 on 1 January 2027. The Corporation Tax Payments page lists both. See Accounting periods longer than 12 months.
Large companies: quarterly instalments
A company with profits above £1.5 million a year pays in four instalments that start during the accounting period, instead of one payment after it. Above £20 million the instalments start earlier still.
| Annual profits above | Instalments due, for a 12-month period | |
|---|---|---|
| Large | £1.5 million | Months 7, 10, 13 and 16 after the period starts |
| Very large | £20 million | Months 3, 6, 9 and 12 after the period starts |
Both limits are divided by the number of associated companies plus one, and reduced for a short period. A company is not treated as large in the first period its profits pass £1.5 million, unless they exceed £10 million, and no instalments are needed when the tax for the period is under £10,000.
Tax Optimiser tests the limits for you. When a company is large or very large it:
- shows a warning on the General tab of the computation, because by the time the return is prepared the instalments are already due;
- marks box 630 (large) or box 631 (very large) on the return;
- lists the instalment dates and amounts on the Corporation Tax Payments page in place of the single date.
The instalments in the computation are based on the final liability. During the year they have to be paid on an estimate, which the company or its adviser works out. HMRC’s guidance is at Corporation Tax: paying in instalments.
How to pay HMRC
Tax Optimiser does not collect or pass on Corporation Tax. Pay HMRC directly, by bank transfer, Direct Debit or through the company’s HMRC online account: see Pay your Corporation Tax bill.
Every payment needs the 17-character payment reference for the accounting period it is for. It is made from the company’s 10-digit UTR followed by seven characters that identify the period, so it changes every period. Using last year’s reference sends the money to last year. You will find it on the “notice to deliver a Company Tax Return” and in the HMRC online account: see HMRC’s guide to the payment reference.
If there is nothing to pay, tell HMRC, or it will send reminders: tell HMRC no payment is due.
Paying late or early
HMRC charges interest on Corporation Tax paid late, from the day after the due date until the day it is paid. There is no separate penalty for paying late; the penalties are for filing the return late. HMRC also pays a lower rate of interest on tax paid early. The rates move with the Bank of England base rate: see Corporation Tax interest charges.
Extra tax from an amended return has the original due date, so interest on it starts from then, not from the date of the amendment.
Keeping a record of payments
Once a return has been filed you can record the payments made against it, so that anyone opening the period can see whether the tax has been settled.
- Open the period and choose Corp Tax Submission to open the filed return.
- On the Payments card, click Add payment.
- Enter a Bank Reference (anything that will help you find the payment on the bank statement), the Payment Date and the Payment Amount, then click Save changes.
The card compares what has been recorded with the Total due on the filed return and shows the balance outstanding, or Paid in full. Add a line for each payment if the tax was paid in parts or by instalments.
Heads up — this is your own record. Nothing here is sent to HMRC or checked against HMRC’s account, and adding a payment does not pay the tax. To see what HMRC has received, check the company’s HMRC online account.
Total due is the Corporation Tax payable recorded for the period when the return was filed. It is refreshed if the computation is saved again or an amended return is accepted.
Common questions
Does filing the CT600 pay the Corporation Tax?
No. The return tells HMRC how much is due. The payment is made separately, directly to HMRC.
Why is the tax due before the return?
The two deadlines are set separately: payment at nine months and one day after the period ends, the return at 12 months. Many companies prepare the return early so the amount is known before the payment date.
Where do I find the Corporation Tax payment reference?
On HMRC’s notice to deliver a Company Tax Return, or in the company’s HMRC online account. It is 17 characters, starts with the UTR and is different for every accounting period.
Can I pay Corporation Tax through Tax Optimiser?
No. Tax Optimiser prepares and files the return and lets you record payments, but the money goes straight from the company to HMRC.
The company made a loss. Do I need to do anything?
There is nothing to pay, but tell HMRC that no payment is due so it does not chase one, and still file the return.
What if I cannot pay on time?
Contact HMRC before the due date. It may agree a payment plan. Interest still runs until the tax is paid.
Is interest on late Corporation Tax an allowable expense?
Yes, for a company. Interest paid to HMRC on late Corporation Tax is deductible as a non-trading loan relationship debit, and interest received from HMRC is taxable.