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HMRC Filing

Corporation Tax (CT600)

Corporation Tax is the tax UK limited companies pay on their profits. The CT600 is the annual return you file with HMRC to report your taxable profits and calculate your tax bill.

Filing Deadline

12 months after year-end

Tax rate 2026-27

19% to 25%

Payment Deadline

9 months + 1 day

Try Tax CalculatorFile with HMRC

Corporation Tax Rates 2026-27

These rates apply to Corporation Tax financial years starting 1 April 2026 (1 April 2026 to 31 March 2027). Since April 2023, Corporation Tax has a tiered structure based on your company's profits. Small companies pay less than larger ones.

£0 - £50,000

Small profits rate

19%

£50,000 - £250,000

Marginal relief

19-25%

£250,000+

Main rate

25%

What is Marginal Relief?

If your profits are between £50,000 and £250,000, you pay the 25% main rate reduced by marginal relief. For 2026-27 the standard fraction is 3/200, so the effective rate rises gradually from 19% to 25% rather than jumping. AccountsOS calculates this automatically.

Important Deadlines

Filing Deadline

12 months

after your accounting period ends. You must file your CT600 return with HMRC.

Payment Deadline

9 months + 1 day

after your accounting period ends. You must pay any Corporation Tax owed.

Example: If your accounting year ends on 31 March 2027:
• Payment due: 1 January 2028 (9 months + 1 day)
• CT600 filing due: 31 March 2028 (12 months)

Reducing Your Tax Bill

Corporation Tax is calculated on your taxable profits, not your total revenue. You can deduct allowable business expenses to reduce your tax bill.

Staff costs (salaries, NI, pensions)
Office costs (rent, utilities, equipment)
Travel and subsistence
Marketing and advertising
Professional fees (accountant, legal)
Software and IT costs
Training and development
Interest on business loans
See all 64 allowable expenses

Late Filing Penalties

HMRC charges penalties for late CT600 returns. These are in addition to interest on any unpaid tax.

1 day late£100
3 months lateAdditional £100
6 months late10% of unpaid tax (min £300)
12 months lateAdditional 10% of unpaid tax

Interest: HMRC also charges interest on late payments at the Bank of England base rate + 2.5%. This adds up quickly on large tax bills.

Calculate Your Corporation Tax

Use our free calculator to estimate your Corporation Tax liability. Enter your profit and see your tax bill instantly.

  • Automatic marginal relief calculation
  • Shows small profits vs main rate
  • Includes payment deadline
  • Compare with previous years
Try Tax Calculator

Example Calculation, 2026-27

Taxable profit£80,000
Tax at the 25% main rate£20,000
Marginal relief (3/200 × £170,000)−£2,550
Corporation Tax£17,450

Effective rate: 21.8%. Profits between £50,000 and £250,000.

How AccountsOS Helps

We track your Corporation Tax liability all year, not just at year-end.

Real-Time Tax Estimate

See your estimated CT liability update as you record transactions. No year-end surprises.

Deadline Reminders

Automatic reminders for both filing and payment deadlines based on your accounting period.

Expense Tracking

AI categorizes your expenses correctly to maximize legitimate deductions.

CT600 Preparation

We prepare your figures for CT600 filing. Just download and submit to HMRC.

Frequently Asked Questions

When do I need to register for Corporation Tax?

Within 3 months of starting to trade. If you've just incorporated, HMRC will contact you, but you should register proactively at gov.uk.

Can I change my accounting year-end?

Yes, you can shorten or extend your accounting period by filing with Companies House. This affects your CT deadlines, so plan carefully.

What if my company makes a loss?

You don't pay CT on losses. You can carry the loss forward to offset against future profits, or in some cases, carry back to previous years.

Do I still need to file if my company is dormant?

Dormant companies may not need to file CT600 returns if they've told HMRC they're dormant. But you still need to file annual accounts with Companies House.

Related Resources

Tax CalculatorAnnual Accounts GuideAll Tax Deadlines

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