Corporation Tax & Companies House

A limited company files two related things after its year end: statutory accounts to Companies House, and a Company Tax Return (the CT600) with tax computations and a copy of the accounts to HMRC. Both the accounts and the computations are filed as iXBRL — a format that is human-readable and machine-tagged so HMRC and Companies House can read the figures automatically.

Corporation Tax is charged on taxable profit, which is your accounting profit adjusted for tax rules (for example, adding back depreciation and applying capital allowances). Valix builds the computation from your accounts and applies the correct rates for the financial year.

Rates and marginal relief

From April 2023 the UK has a small-profits rate and a main rate, with marginal relief tapering between the lower and upper limits. Valix charges the main rate and applies marginal relief as a separate figure on the return, exactly as HMRC’s rules require — reproducing HMRC’s own worked examples (for £100,000 of profit, £2,250 of marginal relief, giving £22,750 of tax).

The CT600 is the corporation tax return. Valix produces a CT600 (version 3) with the iXBRL accounts and computations embedded, validates it against HMRC’s schema and business rules, and files it to HMRC’s Transaction Engine using a submit → poll → confirm process that records HMRC’s digital receipt.

Small companies typically file accounts prepared under FRS 105 (micro-entity) or FRS 102 Section 1A (small entity). Valix prepares statutory accounts from your figures and files the iXBRL accounts to Companies House.