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Indexation Allowance: allows for the effects of inflation when calculating chargeable gains on companies. You apply it to both the cost of the asset itself and any allowable costs of acquisition.

Individual: a person, sole trader, self-employed or a partner in a partnership; individuals are not liable for Corporation Tax.

Inline eXtensible Business Reporting Language (iXBRL): a way of embedding and displaying accounting/financial information in an HTML document, the universal language for web browsers. It allows data to be presented in a readable form, either on screen or in printed output.

Instalment Payments: the instalments (normally four) by which a large company must pay Corporation Tax.

Intangible Assets: include, subject to some exceptions, goodwill and intellectual property such as patents, trade marks, registered designs, and copyright together with licences to exploit such assets and other intangible assets, such as agricultural and fishing quotas.