A company has two important Corporation Tax deadlines to keep in mind: the deadline for paying Corporation Tax and the deadline for filing the Company Tax Return.
Missing either deadline can create unnecessary costs and compliance problems.
Corporation Tax deadlines
For most companies, a Company Tax Return must be filed within 12 months after the end of the accounting period.
Corporation Tax is normally due earlier, at nine months and one day after the end of the accounting period for companies that are not required to pay by quarterly instalments.
For example, if a company’s accounting period ends on 31 March 2026:
- Corporation Tax is normally due by 1 January 2027
- The Company Tax Return is due by 31 March 2027
Here’s the important part: paying the tax and filing the return are two separate obligations.
What happens if the Company Tax Return is late?
Even being one day late can result in a penalty.
For returns with a filing date on or after 1 April 2026, the standard late-filing penalties include:
| How late is the return? | Potential penalty |
| 1 day late | £200 |
| More than 3 months late | A further £400 |
| 6 months late | Further tax-related penalty may apply |
| 12 months late | Further tax-related penalty may apply |
Repeated late filing can lead to significantly higher penalties.
So, filing late isn’t something to ignore simply because the company has already paid its Corporation Tax.
What if Corporation Tax is paid late?
Late payment is different from late filing.
For ordinary Corporation Tax, late-payment interest can be charged when the tax is not paid by the deadline.
Interest generally runs from the date the payment was due until the date it is actually paid. The applicable HMRC interest rate is linked to the Bank of England base rate and can change over time.
This means delaying payment can increase the overall cost, even where a separate late-payment penalty does not apply.
A common mistake companies make
“We’ve filed the return, so we’re done.”
Not necessarily.
A company needs to make sure that:
- The correct Corporation Tax has been calculated.
- The tax is paid by the payment deadline.
- The Company Tax Return is submitted by the filing deadline.
These dates can be different, so businesses should keep track of both.
5 practical tips to avoid Corporation Tax penalties
1. Put both deadlines in your calendar
Don’t only record the Company Tax Return deadline. Set reminders for both the Corporation Tax payment date and the return filing date.
2. Don’t wait until the deadline
Leave enough time to prepare your accounts, calculate the tax and resolve any issues before the deadline.
3. Keep your records updated
Accurate bookkeeping throughout the year can make the year-end Corporation Tax process much easier.
4. Check the tax liability early
Knowing approximately how much Corporation Tax you may owe can help you plan your cash flow and avoid a last-minute payment problem.
5. Don’t ignore HMRC correspondence
If HMRC contacts your company about an outstanding return, payment or penalty, deal with it promptly. Ignoring the issue can make matters more complicated.
Quick check: Is your company ready?
Ask yourself:
Do you know your Corporation Tax payment deadline?
Is your Company Tax Return on track to be filed on time?
Have your accounts and bookkeeping been updated?
Do you know how much Corporation Tax your company is likely to owe?
If you answered “no” to any of these, it may be time to review your company’s tax position.
What if your return is already late?
Don’t leave it sitting there.
If a Company Tax Return is overdue, getting it filed as soon as possible can help prevent further penalties from arising because of continued lateness.
If you believe you had a reasonable excuse for filing late, you may be able to appeal a penalty. The return should generally be filed before making the appeal.
Where a return remains outstanding for six months, HMRC can make a tax determination, estimating the Corporation Tax it believes the company owes. Once the actual return is submitted, HMRC can recalculate the liability and related amounts using the actual figures.
Frequently Asked Questions (FAQs)
1. What is the Corporation Tax payment deadline?
For most companies that are not required to pay by quarterly instalments, Corporation Tax is normally due nine months and one day after the end of the accounting period.
2. When is a Company Tax Return due?
A Company Tax Return is normally due 12 months after the end of the accounting period.
3. Can a company be penalised for filing one day late?
Yes. A Company Tax Return can attract a late-filing penalty even when it is only one day late.
4. Is there a penalty for paying Corporation Tax late?
For ordinary Corporation Tax, late payment generally results in interest being charged, rather than a separate late-payment penalty. The interest continues until the tax is paid.
5. Can I appeal a Corporation Tax late-filing penalty?
You may be able to appeal if the company had a reasonable excuse for filing late. The Company Tax Return should be filed before appealing.
Final thought
Corporation Tax Penalties are often avoidable.
The key is simple: know your deadlines, keep your records organised and don’t leave your tax return until the last minute.
A few hours of planning can potentially save your company from unnecessary penalties, interest and stress.
Need help staying on top of your company’s Corporation Tax and filing deadlines? Speak to a professional accountant before a missed deadline becomes an expensive problem.