CT600 box 55: using estimated figures in a Company Tax Return
Short version. A Company Tax Return can contain estimated figures when final figures are not available. Enter the company's reasonable best estimate as a number, then tick CT600 box 55 to tell HMRC that the return contains an estimate. Do not enter wording such as "information to follow" instead of a figure.
1. What CT600 box 55 means
Box 55 is labelled This return contains estimated figures. HMRC's Company Tax Return guide says to enter an X in box 55 if estimates have been used. It is a disclosure about the figures already in the return. It is not a separate calculation and it does not replace any amount with an estimate for you.
Box 55 is different from box 50. Box 50 says that the company is making more than one return at the same time, which can happen for an accounting period longer than 12 months. Box 55 says that at least one figure in the return is estimated.
2. When to tick box 55
Tick box 55 when the Company Tax Return includes a figure that is estimated rather than final. Examples include:
- closing stock based on a year-end count and the best supplier-cost information available
- turnover reconstructed from the records the company can obtain
- a valuation that cannot be finalised before the filing deadline
- information from a third party that is not yet complete
Do not tick it merely because a figure is rounded in the normal way or because you used accounting judgement to prepare final accounts. The question is whether the return actually contains an estimated figure rather than a final one.
3. Use a reasonable best estimate
HMRC's CTM93280 guidance on estimated figures says an estimate should be reasonable and should represent the company's best assessment using the information available. Placeholder wording instead of a figure does not meet the filing obligation.
Keep the records and working that support the estimate. HMRC's guidance also addresses explaining why an estimate was necessary and, where appropriate, when the figure is expected to be final. SimpleCompanyTax records the box 55 declaration only. It does not collect or transmit a separate explanation for the estimate, so read HMRC's current guidance and consider the company's wider obligations before filing.
4. What box 55 changes
Ticking box 55 does not alter turnover, stock, profit or Corporation Tax. We file the numbers you enter and add the estimated-figures declaration to the Corporation Tax return sent to HMRC. The company remains responsible for the figures and for the existing declaration that the return is correct and complete to the best of its knowledge and belief.
5. How to mark box 55 with SimpleCompanyTax
- Enter the reasonable best-estimate number in the normal field for that figure.
- Go to the bottom of Financial data.
- Find the standalone box 55 declaration after the Employees section.
- Select This Corporation Tax return contains estimated figures (box 55).
- Review the generated Company Tax Return PDF and check that box 55 contains an X.
A long accounting period can produce two Corporation Tax returns. We apply the same box 55 answer to both returns. You can read more about the PDF copies of your filing documents and how the official-form PDF reflects the XML sent to HMRC.
6. When final figures become available
Compare the final figure with the estimate and decide whether the filed return needs correcting. If it does, file an amendment within the applicable time limit. Our guide explains how to amend a CT600. On the amended return, leave box 55 selected only if that replacement return still contains an estimated figure.
This article is general guidance, not tax or accounting advice. If you are unsure whether a figure is a reasonable estimate or whether an amendment is needed, ask an accountant.