Guide

Filing your first company tax return and accounts

Your first year end is the one that catches people out: a period that runs over 12 months, deadlines that fall on different days, and two bodies that each want something. Here is what to have ready, when everything is due, and every step of filing it yourself, shown with a worked example.

Before you start

Two of these come by post, so ask for anything missing first and do the rest while you wait.

Your company number

Eight characters, on your certificate of incorporation. Everything else about the company comes from the public register.

The Corporation Tax UTR

Ten digits, on HMRC letters headed "Corporation Tax". It is not the company number, and not your personal UTR.

A Government Gateway login with Corporation Tax on it

The one for the company's business tax account. Adding Corporation Tax needs an activation code that HMRC posts to the registered office, which can take up to 10 days, so ask for it now if you have not.

The Companies House authentication code

Posted to the registered office when the company was set up. If you cannot find it, Companies House will post a new one, which takes about 5 working days.

The year in figures

Sales, costs, anything you bought to keep (tools, a van, a laptop), and at the year end: the bank balance, what customers owed you and what you owed.

The day you started trading

Only matters when your first accounts run over 12 months, and it decides whether that is one tax return or two. It is the date you gave HMRC when you registered for Corporation Tax.

The example: a first year of 383 days

Hollybank Joinery Ltd is made up, but its first year is typical. It was incorporated on 14 March 2025 and started work straight away. Companies House set its year end to 31 March 2026, the end of the month of its first anniversary, so its first accounts cover 383 days.

Companies House takes one set of accounts for all of that. HMRC cannot: a tax return covers at most 12 months, so the year is two returns, 14 March 2025 to 13 March 2026, then the last 18 days. Why first years run long has the detail, and when a later trading start makes it one return instead.

Two things surprise people. The tax is due before the return is, by about three months, so you cannot wait for the return deadline to find out what you owe. And the two returns are due on the same day, but their tax is not. Your Companies page lays it out like this for each company:

Filing it, step by step

Eight steps, saved as you go, so you can stop and come back on any device. Nothing is sent anywhere until the very last button.

1Find your company

Type the company number and the wizard fills in the name, the registered office and the accounting dates from Companies House.

2Does it fit?

Ten questions that decide whether this is a company we can file for: a small company with one trade, no audit, no group. Answer honestly. If something rules it out you find out now, not after an hour of figures. Say yes to the last one if a director owes the company money; it brings up the director's loans section later.

3What to file

Most companies need both: the CT600 to HMRC and the accounts to Companies House. Both cost the same £49 as either one. Keeping the profit and loss private (filleted accounts) is normal for a small company: the public register then shows only the balance sheet, while HMRC still gets the full accounts.

4Profit and loss

The period dates come from the register. Because Hollybank's accounts run over a year, the wizard asks when it started trading. It traded from the start, so the box stays as it is, and the wizard spells out the two returns that follows. If an accountant or you already filed the first one, say so here and only the second is sent.

Then the year's figures, as totals for the whole 383 days: sales, costs, staff (a director's salary counts), and anything bought to keep, which goes under "Equipment bought". The tax updates on the right as you type, for each return and in total.

If a director owes the company money

Money the company lent a director, or that a director took out beyond salary and dividends, is a director's loan. If any is still owed at the year end, HMRC charges a temporary tax on it (33.75%, or 35.75% on loans made from 6 April 2026), and gives it back once the loan is repaid. Repay it within 9 months and a day of the year end and the charge never has to be paid at all. Fill in who owes what, and what was repaid since.

5Balance sheet

What the company owned and owed on the last day of the period: equipment, cash at the bank, money customers owed, and bills not yet paid. In a first year there is no previous year to compare with. In later years, if accounts for the same period are already on the register, the wizard reads them and offers "Use the filed figures", because the tax return should match the accounts that were filed.

6Review

Both returns side by side. Hollybank's £32,100 of taxable profit splits into £30,422 for the first 365 days and £1,678 for the last 18, so £5,780 and £319 of tax: £6,099 in all. Check every figure here; this is what the returns will say.

7Declaration

The UTR, who is declaring the return, which director signed the accounts and when the board approved them (for a one-director company, the day you approve them), and a few words on what the company does, which is printed on the accounts.

8Your filing pack, then file

Every document that will be sent, generated from what you entered: the accounts for HMRC, the filleted accounts for Companies House, the tax computations and each CT600 on HMRC's own form. Open any of them before you file.

Pay the £49, then enter the company's Government Gateway login and the Companies House authentication code. The login is used once to send the returns and is never stored. Tick the two confirmations and file: the returns go to HMRC first, and the accounts follow to Companies House a minute or two after HMRC accepts.

If the first return is already filed

Some first-year companies have the first 12 months filed by an accountant, or filed it themselves somewhere else, before the last few weeks catch up with them. Answer yes to "Has the first return already been filed with HMRC?" in step 4 and we send only the second, still with the full accounts attached, as HMRC expects.

HMRC does not tell anyone else which returns it has, so the Companies page cannot know about one filed elsewhere. Once the accounts are filed, each return has its own "I have already filed it", and the one you mark stops counting down:

Mistakes we have seen

• The start date a year late. Typing 14 March 2026 for 14 March 2025 leaves an 18-day period holding the whole year's profit. The small profits limit shrinks with the period, to about £2,500 for 18 days, so all £32,100 is taxed at 25%: £8,025 instead of £6,099. The wizard checks the dates against the register and says so:

• Filing only the last few weeks. Entering just the 18 days, as if they were the whole year, attaches 18 days of accounts to the return and leaves the first 12 months unfiled. The wizard recognises that shape and explains both ways to fix it.
• A balance sheet left at zero. If accounts for the period are already on the register, the return should agree with them. The wizard compares the two and offers the filed figures.
• Thinking Companies House tells HMRC. It does not. Accounts filed at Companies House are not a tax return, and HMRC's late-filing penalties start the day after the return is due. See the three deadlines.

After you file

• HMRC answers within minutes. We email you when it has the returns and again when it accepts them, with how much tax to pay for each period, by when, and HMRC's bank details.
• A Companies House examiner then checks the accounts, which can take a few days. We email you when they are accepted.
• Pay the tax by each return's own date. Each tax period has its own payment reference, so two returns means two references; HMRC shows them in the company's business tax account. Use the right one for each payment, or HMRC credits it to the wrong period.
• From the second year on it is simpler: periods of 12 months, one return each, and the deadlines on your Companies page.

Illustration only, simplified for clarity. Real returns can differ. This page explains the mechanism; it is not tax or accountancy advice, and the figures on any return remain the company's responsibility.