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HMRC internal manual

COTAX Manual

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HM Revenue & Customs
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Assessing: CTSA assessments: arithmetical and other errors in self assessments

Validation rules make sure that the figures on the CT600 of a return submitted through the CT Online Service are arithmetically correct. However, function RAMA (Record / Amend Assessment) automatically checks the figures and can correct any that are wrong. (This content has been withheld because of exemptions in the Freedom of Information Act 2000)  (This content has been withheld because of exemptions in the Freedom of Information Act 2000) .

In RAMA, COTAX displays a screen with:

  • the figures entered from the return displayed in blue on the left side, which you cannot change
  • the figures calculated by COTAX displayed in black on the right side of the screen, which you can change.

If COTAX has corrected an arithmetical error, the figure is highlighted in magenta.

You can change entries or make new ones using the [Amend] button.

COTAX does not let you enter a figure that is arithmetically incorrect or does not comply with its validation rules. For example, if you try to change the financial years so that they are not correct for the AP, COTAX changes your figures to the correct ones and redisplays them to you using the appropriate colour combination (Word 28KB).

If you try to enter a figure for marginal relief and COTAX calculates that it is not due, it removes the figure without highlighting the change.

(This content has been withheld because of exemptions in the Freedom of Information Act 2000)

You may want to record the self assessment exactly as captured from the return where the company’s calculation is correct but, for example, COTAX ‘corrects’ the tax rate to the small profits rate when the case is a close investment holding company within Part 3 Section 34 CTA 2010 and therefore liable at the main CT rate.

Provided the figure you enter is entered as a whole number or a decimal as appropriate, COTAX lets you replace its recalculated figure but highlights the entry in green.

See:

  • COM23011 for a list of forms relevant to this subject
  • COM23012 for a list of functions to use in particular situations
  • COM23013 for legislation applying to this subject.