What's the difference between annual accounts and a corporation tax return?

Annual accounts show your company’s financial performance and are filed with Companies House — they’re publicly available. Your corporation tax return calculates the tax you owe and is filed with HMRC — it stays private. Both are required, and both have different deadlines. We can help with both through our Limited Company Accounts and Corporation Tax Return services.

Can I file my own corporation tax return?

You can, and there’s software that makes it possible. But working out allowable expenses correctly takes experience, and mistakes can be costly. Most limited company directors find it’s worth having an accountant handle it.

What counts as an allowable expense?

An expense is allowable if it’s “wholly and exclusively” for the purpose of the business. Common examples include office supplies, software subscriptions, professional fees, and staff training. But some things that feel business-related — like depreciation or certain entertainment costs — aren’t allowable. We can help you understand what applies to your situation.

Do dormant companies need to file?

Yes. Even if your company hasn’t traded, you still need to file a nil corporation tax return. The only transactions a dormant company can have are things like filing fees or shares issued at incorporation. Anything beyond that means the company is considered to be trading.

Is the payment deadline before the filing deadline?

It catches a lot of people out, but yes, you need to pay your corporation tax 9 months and 1 day after your year-end, while the return itself isn’t due until 12 months. This means you need to have a good estimate of what you owe before you’ve formally filed. Working with an accountant helps you stay ahead of both deadlines.

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Corporation Tax Returns

Your company’s tax return, filed accurately and on time — with a clear breakdown of what you owe and why.

Who needs to file a corporation tax return?

Every UK limited company needs to file a corporation tax return with HMRC, even if the company made no profit or owes no tax. This includes dormant companies, which still need to submit a nil return.

Community Interest Companies (CICs) also fall under this requirement.

If you run a limited company, this is one of the filings you can’t skip.

What is a corporation tax return?

A corporation tax return — also known as a CT600 — is how your company reports its profits and calculates the tax it owes to HMRC. Think of it as a self-assessment, but for your company rather than you personally.

What’s included in a corporation tax return, and who can see it?

The return is based on your company’s annual accounts. It takes the financial picture from those accounts and works out how much corporation tax is due, factoring in things like allowable expenses and capital allowances.

Unlike your annual accounts (which are filed with Companies House and available to the public), your corporation tax return goes to HMRC and stays private.

When to file your corporation tax return

There are two deadlines to be aware of:

Filing deadline: 12 months after your company’s financial year-end
Payment deadline: 9 months and 1 day after your financial year-end

The payment deadline comes first, which catches some people out. You need to pay what you owe before you’re required to file the return itself.

A practical approach is to aim for both by the 9-month mark — that way, you’ve got everything sorted in one go.

How corporation tax returns work

Your corporation tax return starts with your annual accounts. From there, adjustments are made to arrive at your taxable profit — this isn’t always the same as the profit shown in your accounts.

Working out your tax-deductible expenses

Some expenses that appear in your accounts aren’t “allowable” for tax purposes. The most common example is depreciation: it’s a valid expense in your accounts, but HMRC doesn’t accept it for tax. Instead, you claim capital allowances, which work differently.

Working out what’s allowable and what isn’t is where things get technical. The general rule is that an expense must be “wholly and exclusively” for the business — but applying that rule to real-world situations takes experience.

Why corporation tax returns matter

Filing late or incorrectly can result in penalties and interest charges. More importantly, getting your return wrong — particularly around allowable expenses — could mean paying more tax than you need to, or facing questions from HMRC later.

A well-prepared return makes sure you’re claiming everything you’re entitled to, while staying on the right side of the rules.

Corporation Tax Returns

CT600 preparation and filing
Calculation of tax due
Review of allowable expenses and capital allowances
Clear explanation of what you owe and when
Deadline tracking and reminders

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Your Corporation Tax Returns with Watmore & Co

We prepare your corporation tax return based on your annual accounts, making sure all the adjustments are handled correctly. You’ll get a clear breakdown of how we arrived at the figure, not just a number and a bill.

Corporation Tax and Limited Company Accounts

If you’re also using us for your Limited Company Accounts, the two work together seamlessly — we already have the information we need, and the process is straightforward.