Journey

File your first Corporation Tax return

A step-by-step learning journey for directors filing their first Company Tax Return (CT600). Covers registration, understanding rates, preparing accounts, claiming allowances, filing, and paying Corporation Tax.

Running a Business Updated 15 September 2026

6 milestones references 7 guides

Your first Corporation Tax return

As a limited company director, you must file a Company Tax Return (CT600) with HMRC and pay Corporation Tax on your company's profits. This journey walks you through the entire process from registration to payment.

Your first return covers the accounting period from when your company started trading to your chosen year-end date.

Register for Corporation Tax

Before you can file a return, your company must be registered with HMRC for Corporation Tax. You should have done this within 3 months of starting to trade.

Register your company for Corporation Tax

How to register with HMRC, what information you need, and what happens after registration.

Registration deadline

You must register within 3 months of starting business activity. If your company is already incorporated but not yet trading, you do not need to register until you begin trading.

Registration deadline

Within 3 months of starting to do business

What counts as starting

Buying, selling, advertising, renting property, employing someone

UTR delivery

10-digit Unique Taxpayer Reference sent by post after incorporation

Set up your company for Corporation Tax (opens in a new tab)
Understand your Corporation Tax rate

The rate you pay depends on your company's taxable profits. Most new companies with modest profits will pay the small profits rate.

Corporation Tax basics

An overview of Corporation Tax rates, marginal relief, and how the system works.

Corporation Tax rates and small profits relief

Detailed rates, marginal relief calculation, and worked examples showing how thresholds work.

Current rates at a glance

Check whether your profits fall in the 19% small profits band, the 25% main rate band, or the marginal relief zone between them.

Main rate (25%)

Applies to profits over £250,000 (from 1 April 2023)

Small profits rate (19%)

Applies to profits of £50,000 or less

Lower threshold

£50,000 (small profits rate eligibility)

Upper threshold

£250,000 (main rate applies above this)

Marginal relief band

£50,000 to £250,000 (tapered effective rate 19%-25%)

Associated companies rule

Thresholds divided equally by number of associated companies

The Corporation Tax rate structure changed significantly from 1 April 2023 under Finance Act 2022. The main rate increased from 19% to 25% for profits over £250,000, while small companies with profits up to £50,000 retained the 19% rate. Companies with profits between £50,000 and £250,000 benefit from marginal relief, which provides a gradual transition between the two rates.
Associated companies: If you have associated companies (connected businesses under common control), the profit thresholds are divided equally by the total number of companies. For example, with 2 associated companies, the small profits threshold becomes £25,000 each.

Corporation Tax rates (opens in a new tab)
Claim capital allowances

If your company has purchased equipment, vehicles, or other assets, you can claim capital allowances to reduce your taxable profit. Do not overlook this - it is one of the most valuable reliefs available.

Claim capital allowances for your company

How to claim AIA, full expensing, and writing down allowances on your CT600.

Annual Investment Allowance

Most new companies can claim 100% tax relief on qualifying plant and machinery up to the AIA limit in the year of purchase.

AIA permanent limit

£1,000,000 per year (100% first-year relief on qualifying expenditure)

Qualifying assets

Most plant and machinery, including computers, office furniture, vans, tools, and equipment

Excluded from AIA

Cars, assets given to you, items you owned before using in business, and items bought in final accounting period before cessation

Associated companies

AIA shared equally between associated companies (e.g., 2 companies = \xA3500,000 each)

Short accounting periods

AIA pro-rated for periods shorter than 12 months

Effective date

Permanent from 1 April 2023 (previously fluctuated between \xA325,000 and \xA31,000,000)

The Annual Investment Allowance (AIA) gives 100% tax relief on qualifying plant and machinery expenditure in the year of purchase, up to the annual limit. This is the most straightforward capital allowance and should be used first before considering other allowances.
Order of priority: Claim AIA first on special rate pool items (which would otherwise only get 6% WDA), then on main rate pool items. Full expensing may be more beneficial for main rate pool assets in some cases as it has no annual cap.

Claim capital allowances (opens in a new tab)
Prepare and file your CT600

Your Company Tax Return must be filed within 12 months of the end of your accounting period. You will need finalised accounts in iXBRL format and your tax computation.

File your Company Tax Return (CT600)

What to include in your return, iXBRL requirements, and how to submit through HMRC's online service.

Filing deadline

The CT600 must be filed within 12 months of your accounting period end. Your first accounting period starts when you begin trading, not when you incorporated.

Payment deadline

9 months and 1 day after accounting period ends

Filing deadline

12 months after accounting period ends

Example: Year end 31 March 2025

Pay by 1 January 2026, file by 31 March 2026
Pay your Corporation Tax
Corporation Tax must be paid 9 months and 1 day after your accounting period ends - this is before the CT600 filing deadline. Do not wait until you file to pay.

Plan your Corporation Tax payments

Payment methods, deadlines, and what to do if you cannot pay on time.
Payment deadline

The payment deadline is earlier than the filing deadline. Make sure you set aside funds throughout the year to avoid a cash flow shock.
Corporation Tax is due 9 months and 1 day after your accounting period ends. This is earlier than the CT600 filing deadline (12 months), so you must pay before submitting your return.

Standard payment deadline

9 months and 1 day after accounting period ends

Filing deadline (CT600)

12 months after accounting period ends

Example: 31 March year end

Pay by 1 January, file by 31 March following year

Example: 31 December year end

Pay by 1 October, file by 31 December following year

Interest on late payment

Bank of England base rate + 4% (currently 7.75%)

Repayment interest

Bank of England base rate - 1% (if HMRC owes you)

Large company exception: Quarterly instalments
Companies with profits over £1.5 million cannot wait 9 months - they must pay in quarterly instalments during and after the accounting period.
Quarterly instalment thresholds:
£1.5m - £20m profits: Pay in 4 instalments (months 7, 10, 13, 16)
Over £20m profits: Pay earlier (very large company rules)
Associated companies: The £1.5m threshold is divided by the number of associated companies. With 2 associated companies, the threshold becomes £750,000 each.

Practical payment tips
Set up a tax reserve: Transfer estimated Corporation Tax monthly to avoid cash flow shock
Use HMRC online payment: Fastest method - allows payment up to deadline day
Bank transfers take time: BACS takes 3 working days, Faster Payments is same day
Cheques are risky: Must be received and cleared by deadline - allow 6+ working days
Interest runs from day 1: Even one day late triggers interest charges

Pay your Corporation Tax (opens in a new tab)
Verify your compliance

Use the compliance checklist to make sure you have not missed anything. Getting your first return right sets a good foundation for future years.

Corporation Tax annual compliance checklist

A complete checklist covering accounts, filing, payment, record keeping, and Companies House obligations.

File your first Corporation Tax return

Your first Corporation Tax return

Register for Corporation Tax

Register your company for Corporation Tax

Understand your Corporation Tax rate

Corporation Tax basics

Corporation Tax rates and small profits relief

Claim capital allowances

Claim capital allowances for your company

Prepare and file your CT600

File your Company Tax Return (CT600)

Pay your Corporation Tax

Plan your Corporation Tax payments

Verify your compliance

Corporation Tax annual compliance checklist

Related journeys

Corporation Tax quick compliance check

Manage your tax compliance

Respond to a Corporation Tax penalty or enquiry

Set up a limited company