Corporation Tax Deadlines Calendar 2026

Missing a Corporation Tax deadline costs real money — late filing penalties start at £100 (£200 for filing deadlines from 1 April 2026) and escalate fast, while late payment interest accrues daily. This complete 2026 calendar lays out every key date so you can plan ahead and avoid unnecessary charges.

How Corporation Tax deadlines work

Before the calendar, let's recap how deadlines are calculated. Every company's deadlines are based on its accounting period end date (not the calendar year or tax year):

• Corporation Tax payment: Due 9 months and 1 day after the end of the accounting period
• CT600 filing: Due 12 months after the end of the accounting period — the anniversary of your year-end
• Penalties kick in: The day after the filing deadline

Watch out for weekends and bank holidays. The rules work differently for payments and filing:

• Payments: the deadline does not move. If it falls on a weekend or bank holiday, your money must reach HMRC on the last working day before the deadline — unless you pay by Faster Payments, which clears on weekends and bank holidays too.
• Filing: the CT600 is filed online, and HMRC's filing service runs every day of the year, so the deadline date stands regardless of which day of the week it falls on.

For a detailed breakdown of filing deadlines, see our CT600 deadline guide.

2026 month-by-month calendar

The tables below show deadlines falling in each month of 2026, based on the most common accounting period end dates.

January 2026

New Year's Day note: 1 January 2026 is a bank holiday (Thursday). The payment deadline does not move — unless you pay by Faster Payments, your payment must reach HMRC by Wednesday 31 December 2025, the last working day before. Don't leave it to 2 January: by then you're already late and interest is running.

February 2026

1 February 2026 is a Sunday — so unless you're paying by Faster Payments, your payment needs to reach HMRC by Friday 30 January. Otherwise February is relatively quiet for Corporation Tax. Use this month to prepare if your company has a 31 March year-end — your payment was due 1 January and your CT600 is due by 31 March.

March 2026

31 March is one of the busiest dates in the Corporation Tax calendar. It's the most popular year-end for UK companies, so HMRC's systems can experience heavy traffic. Don't leave filing to the last day. It's also the last filing deadline under the old £100 penalty regime — returns with filing deadlines from 1 April 2026 attract doubled penalties (see below).

April 2026

April changes: Corporation Tax rates for financial year 2026 stay at 19% for profits up to £50,000 and 25% above £250,000, with marginal relief in between. If your accounting period straddles 1 April, profits are apportioned between financial years — which only matters in years when the rates actually change. See our Corporation Tax rates guide. The bigger April change is penalties: fixed late filing penalties double for returns with filing deadlines on or after 1 April 2026.

May 2026

June 2026

Mid-year review: If your company has a 31 March year-end, June is a good time to do a mid-year tax review. Assess your projected profits and plan any year-end tax planning strategies.

July 2026

August 2026

Summer holiday warning: Many directors take August holidays and forget about impending deadlines. If your year-end was 31 October 2025, your tax payment is due 1 August — a Saturday in 2026, so unless you use Faster Payments it must reach HMRC by Friday 31 July. Set a reminder before you go away. 31 August is also a bank holiday, but the filing deadline stands — HMRC's online filing service is available throughout.

September 2026

October 2026

Companies with 31 December year-ends: Your tax payment is due 1 October, but your CT600 filing isn't due until 31 December. Don't wait until filing to calculate what you owe — use a Corporation Tax calculator to estimate your liability and pay on time.

November 2026

1 November 2026 is a Sunday — payments (other than Faster Payments) must reach HMRC by Friday 30 October.

December 2026

Christmas period: HMRC's online systems remain available over Christmas, but telephone support has reduced hours. If you need to contact HMRC about your Corporation Tax account, do so before mid-December.

Quarterly instalment dates for large companies

If your company's augmented profits exceed £1.5 million (taxable profits plus most dividends received), it counts as "large" and must pay Corporation Tax in quarterly instalments during the accounting period rather than waiting until 9 months after. The £1.5 million threshold is divided by the number of associated companies plus one and prorated for short accounting periods — so a company with two associated companies hits the instalment regime at just £500,000 of augmented profits.

For a 12-month accounting period, the four instalments fall roughly in months 7, 10, 13 and 16 from the start of the period. For companies with a 31 March 2026 year-end, the quarterly instalment dates are:

For companies with a 31 December 2025 year-end:

Very large companies (augmented profits over £20 million, again adjusted for associated companies) must pay even earlier — instalments start in the third month of the accounting period. See our quarterly instalments guide for the full rules.

Late filing penalties

There are now two penalty regimes, depending on when your filing deadline falls. The fixed penalties doubled for returns with filing deadlines on or after 1 April 2026:

If you file late for three consecutive periods, the fixed penalties increase — to £500 each under the old regime and £1,000 each under the new one.

You can appeal a late filing penalty if you have a reasonable excuse, but HMRC sets a high bar. "I forgot" or "I didn't know" won't usually succeed.

For the full breakdown, see our penalties guide.

Late payment consequences

There are no fixed penalties for paying Corporation Tax late (outside the quarterly instalment regime) — but late payments attract interest, charged from the day after the payment deadline until the day you pay. HMRC's late payment interest rate is set at the Bank of England base rate plus 4% — 7.75% since 9 January 2026.

Interest is simple, calculated daily — it doesn't compound. Even so, it adds up: being a week late on a £10,000 liability costs around £15, and a £50,000 liability paid three months late costs nearly £1,000.

See our guide on Corporation Tax interest for current rates and how to calculate what you owe.

Payment methods and processing times

When paying close to a deadline, choose your payment method carefully:

Note that HMRC accepts corporate credit cards online (with a fee) but not personal credit cards.

Tip: Always use your correct payment reference number when paying — it's the 17-character reference on your HMRC payslip and changes for every accounting period. The wrong reference can mean your payment isn't allocated to your account, and you'll appear to have paid late.

For full instructions, see our guide on how to pay Corporation Tax.

Key dates to remember for 31 March year-end companies

Since 31 March is the most common year-end, here's a focused summary for these companies:

For the year ending 31 March 2026:

For the year ending 31 March 2025 (filing in 2026):

How to avoid missing deadlines

1. Set calendar reminders

Add your payment and filing deadlines to your calendar with reminders at:

• 3 months before (start preparing)
• 1 month before (finalise accounts)
• 1 week before (file and pay)

Remember to check whether the payment deadline falls on a weekend or bank holiday — if it does, and you're not paying by Faster Payments, your real deadline is the last working day before.

2. Track both deadlines separately

The payment deadline arrives three months before the filing deadline — a common trap. Many directors work towards the filing date and only then discover the tax was due months earlier, with interest already running. Treat 9 months + 1 day as the date that matters most.

3. File early

There's no advantage to waiting until the deadline. File your CT600 as soon as your accounts are ready — many companies file within a few months of their year-end, giving them a comfortable buffer. When you're ready, Taxpipe walks you through your CT600 step by step and files it directly with HMRC through your Government Gateway account for a flat £59 — no need to know box numbers.

4. Pay early if in doubt

If your accounts aren't finalised but you have a rough idea of your Corporation Tax liability, consider paying an estimated amount before the deadline. You can claim a refund if you overpay, and HMRC will pay you repayment interest on the overpayment (2.75% since 9 January 2026).

5. Appoint a tax agent

An accountant or tax agent can manage deadlines for you, receiving HMRC reminders and handling filings on your behalf.

Special situations

New companies

Your first accounting period might not align with a standard 12-month cycle. Check your specific dates carefully — see our new company timeline guide for worked examples.

Companies changing their year-end

If you change your accounting period, your deadlines change too. The transitional period will have its own unique payment and filing dates.

Companies being struck off or dissolved

If your company is being closed down, you still need to file a final CT600 covering the period up to the date of cessation. Don't assume dissolution removes the filing obligation.

Frequently asked questions

What if the deadline falls on a weekend or bank holiday?

For payments, the deadline doesn't move — your payment must reach HMRC on the last working day before the weekend or bank holiday, unless you pay by Faster Payments (which processes every day, including weekends and bank holidays). For filing, the CT600 is submitted online and HMRC's service runs every day, so you can file on the deadline itself whatever day it falls on — though leaving it that late is never wise.

Can I get an extension to file my CT600?

HMRC doesn't grant extensions for CT600 filing. The 12-month deadline is considered generous compared to other taxes. If you genuinely cannot file on time, file as soon as possible to minimise penalties and consider appealing on the basis of a reasonable excuse.

Do I need to file if my company made a loss?

Yes. You must file a CT600 regardless of whether your company made a profit or loss. A loss return is important because it establishes your loss carry-forward position for future years.

When does HMRC's interest start on late payments?

Interest accrues from the day after the payment deadline. If your payment was due on 1 January 2026 and you pay on 15 January 2026, you owe 14 days of interest — simple daily interest at 7.75% on the outstanding amount.

Is there a deadline for amending a CT600?

Yes — you can amend a CT600 up to 12 months after the original filing deadline. For a 31 March 2025 year-end, the filing deadline is 31 March 2026, so the amendment deadline is 31 March 2027. See our CT600 amendments guide for the process.

What happens if my company is dormant?

If HMRC has been notified that your company is dormant, you won't need to file CT600s unless HMRC issues a notice to deliver a return. However, you must notify HMRC promptly when the company becomes active again.

Related guides

• Corporation Tax Deadlines 2026: When You Need to File and Pay
• CT600 Deadline: When Is Your Company Tax Return Due?
• CT600 Penalties: What Happens If You File Late?
• How to Pay Corporation Tax to HMRC
• CT600 Deadline: When to File Your Corporation Tax Return

Related Reading

• Corporation Tax Deadlines 2026: When You Need to File and Pay
• The Cheapest Way to File Your CT600 in the UK (2026)
• Corporation Tax Payment: Deadlines, Methods & What Happens If You're Late