Corporation tax deadline for limited companies: CT600 filing, payment dates and penalties

There are two separate deadlines:

HMRC works in accounting periods for Corporation Tax. For most companies, an accounting period is based on your statutory accounts period, but it is not always identical.

Key points directors miss:

• A Corporation Tax accounting period cannot be longer than 12 months. If your first set of accounts covers more than 12 months, you will have two accounting periods for Corporation Tax.
• Your “year end” in your accounts is not automatically the end of your first Corporation Tax period if your first accounts are long.
• The deadlines are calculated from the end of the Corporation Tax accounting period, not the date you incorporated and not the date you filed accounts at Companies House.
• If you are unsure what your accounting period end date is for HMRC purposes, do not guess. This is where professional advice usually becomes worthwhile because the deadlines and returns follow from this starting point.

Companies House uses your accounting reference date (your Companies House year-end). HMRC uses your Corporation Tax accounting period.

They often align, but they can drift because:

• Companies House filing deadlines are based on incorporation date and the accounting reference date.
• HMRC deadlines are based on the accounting period end date for Corporation Tax (and can split in year one).
• Changes to your year-end can create short periods, long periods, or overlaps that change the deadline pattern.

A common “gotcha” is when a director assumes “accounts filed” means “tax sorted”. Companies House acceptance does not tell you anything about whether your CT600 filing is complete, correct, or on time.

For most small and medium UK companies, the corporation tax payment deadlin is typically 9 months and 1 day after the end of the Corporation Tax accounting period.

Payment is due even if you have not finalised the CT600 yet. You can refine the figure later if needed, but you should not be “waiting for the return” to pay, and no, “I didn’t know how much it would be” is not a defence. HMRC expects companies to estimate and manage cash flow.

The company tax return deadline (the CT600 deadline) is usually 12 months after the end of the Corporation Tax accounting period. This is a filing deadline, not a payment deadline. You can file your return earlier, and for well-run companies it is normal to file well before the 12-month limit.

You usually need to submit:

• The CT600 (Company Tax Return),
• Statutory accounts in the required format, and
• A Corporation Tax computation.

HMRC expects the numbers to reconcile. In practice, that means:

• Your statutory accounts show the accounting profit and key disclosures.
• Your tax computation explains the adjustments from accounting profit to taxable profit.
• Your CT600 is the summary return that ties those figures together and includes claims, elections, and supporting boxes.

Where things go wrong is when directors see “accounts done” and assume that is enough. A set of accounts, on its own, is not a tax return. HMRC expects the computation and CT600 to be consistent with those accounts.

Late compliance is expensive for two reasons:

• HMRC charges penalties and interest, and
• Lateness tends to create messy records.

These are different issues:

• Late filing penalties apply when you miss the CT600 filing deadline.
• Late payment interest applies when you miss the corporation tax payment deadline.

For CT600 late filing, the standard penalty pattern starts small and escalates from an initial fixed penalty, to another fixed penalty after a period of lateness, then percentage-based penalties and HMRC can issue a tax determination if the return is very late.

For late payment, interest starts running from the payment due date. HMRC does not “pause” interest because you are waiting on accounts, waiting for invoices, or hoping to sort it later.

Not being able to pay on time is not unusual. What matters is what you do next. If the company cannot pay Corporation Tax by the deadline, the sensible approach is:

• File what you can file on time (or as soon as possible),
• Quantify the liability as accurately as possible (even if provisional), and
• Speak to HMRC early about options, including a Time to Pay arrangement if appropriate.

The two worst patterns are:

1. Ignoring HMRC letters until the problem becomes enforcement.
2. Guessing figures or filing “something” that you know is wrong, hoping to tidy it up later.

If you do not know the number, it is better to produce proper accounts and a defensible estimate than to invent a liability. HMRC can be pragmatic with genuine difficulty, but it is not sympathetic to avoidance-by-delay.

Dividends must be paid from distributable reserves (retained profits). Two common misunderstandings a:

• Cash in the bank is not the same as retained profit, and
• “We had a good month” does not prove you have distributable reserves.

If you take dividends without sufficient reserves, they can be reclassified (often into a director’s loan account), the company’s accounts can become harder to prepare and you can create a personal tax problem, not just a company tax problem.

At this point, most directors involve an accountant to confirm whether dividends were legal and what corrections are needed.

If you take money out without a clear label (salary, dividends, repayment of money you put in), it usually ends up in the director’s loan account.

An overdrawn director’s loan account can trigger:

• additional Corporation Tax charges (for certain loans outstanding after a set period),
• benefit-in-kind reporting if the balance exceeds a threshold,
• difficult clean-ups when accounts are finalised.

If your bookkeeping does not track the director’s loan account monthly, you are flying blind.

If you want fewer surprises, treat Corporation Tax as a year-round process, not a year-end panic. A practical director-level checklist would be:

1. Confirm the company’s Corporation Tax accounting period end date(s).
2. Diarise two dates: payment deadline and CT600 filing deadline.
3. Keep bookkeeping up to date (monthly is the minimum if you want control).
4. Track dividends, salary, expenses, and director’s loan account movements as you go.
5. Build a rough tax provision during the year so cash is available.
6. If you cannot pay, speak to HMRC early – and do it with numbers, not guesses.

Key risks to keep in mind:

• Missing the distinction between the corporation tax payment deadline and the CT600 deadline
• First-year accounting periods creating two deadlines when you expected one
• Taking dividends or drawings without checking reserves and director loan positions
• Letting lateness become a pattern that attracts scrutiny

Practical next step: review your accounting period end date, diarise both deadlines, and ask your accountant to confirm (in writing) what will be filed and paid, and when.