Correcting a filing after it was accepted: the CT600, accounts, Self Assessment, VAT and the confirmation statement

The Company Tax Return

A company usually has to amend its CT600 within 12 months of the filing deadline¹. The filing deadline is 12 months after the end of the accounting period the return covers², so for a year ending 31 March 2026 the return is due by 31 March 2027 and can be amended until 31 March 2028. You amend it through commercial software, or by posting a paper return to the Corporation Tax office¹.

Once that window has closed, what you do depends on which way the mistake went. If the company overpaid Corporation Tax, it may be able to claim the money back through overpayment relief. If it underpaid, tell HMRC through its online disclosure service as soon as you can¹. HMRC may check a return for errors and can charge a penalty for them¹.

If the accounts are wrong too, they are corrected at Companies House separately: HMRC and Companies House keep their own copies.

The director’s Self Assessment

A Self Assessment return can be amended within 12 months of the Self Assessment deadline, online or by sending another paper return. For the 2024 to 2025 tax year, that usually means by 31 January 2027³. After that, a director who paid too much can claim overpayment relief up to 4 years after the end of the tax year it relates to, in writing, with the tax year, why they think they overpaid and how much³.

A VAT return

VAT errors are usually corrected on a later return, not by amending the one already sent. There are two ways⁴:

• On your next return: when the net value of the errors is £10,000 or less, or up to £50,000 as long as it is no more than 1% of the box 6 (net outputs) figure on the return where you correct it⁴.
• Told to HMRC separately: when the errors are bigger than that, or were made deliberately. HMRC takes these through its online error notification service or in writing⁴.

Errors can only be corrected for up to 4 years, counted from the end of the accounting period for tax you under-declared or reclaimed too much of, and from the return’s due date for VAT you didn’t reclaim. The 4-year limit doesn’t apply to deliberate errors⁴.

Accounts at Companies House

Amended accounts must be for the same period as the originals, and they replace them: they say they replace the original accounts, are now the statutory accounts and are prepared as they were at the date of the originals. The originals stay on the public record⁵. On paper, write “amended” on the front so Companies House doesn’t treat them as a duplicate; if only part of the accounts needs correcting, a note signed by a director can describe the change instead⁵. Filing software can send amended accounts only if you used it for the originals and it supports them⁵.

The confirmation statement

There’s no way to edit a confirmation statement that has been filed. If something in it was wrong, such as the SIC code, file another confirmation statement with the right details. You pay once per 12-month payment period and can then file as many as you need in it⁶. Changes to directors, the registered office or people with significant control have their own forms. See confirmation statement cost.

Correcting a filing with Fileyear

If Fileyear filed it, start with Amend on the filing’s page. Fileyear copies the filing as it was sent, you change what was wrong, check it and approve it, and pay that filing’s usual price. It sends only what changes: an amended CT600, amended accounts, or both, or an amended Self Assessment return, and it won’t start one after the deadline for amending has passed. VAT errors within the limits are entered on your next VAT return.

An amendment costs the same as the original filing. The one exception is free: a CT600 filed with tax on a director’s loan made from 6 April 2026 at 33.75%, the most HMRC’s online service took at the time, needs amending to the 35.75% rate once HMRC takes it. Fileyear emails you when it does, with the amendment ready to send at no charge. See director’s loan accounts and s455.