Digital accounts and iXBRL: the filing changes coming for small UK companies in 2026–2028

Inline eXtensible Business Reporting Language (iXBRL) is a digital accounting format in which every line of your accounts carries a machine-readable tag. Rather than submitting a PDF that HMRC staff read manually, iXBRL-tagged accounts allow HMRC's systems to process the data directly. Large UK companies have been required to file iXBRL-tagged accounts with their corporation tax returns since 2011. The extension of this requirement to small companies has been in progress since 2020 and is now entering its final phases.

Where the current rules stand: companies filing corporation tax returns via commercial accountancy software (Xero, QuickBooks, Sage, CCH, IRIS, and similar) almost certainly already produce iXBRL-compliant output — these platforms have built iXBRL tagging into their accounts-production tools. The gap has been companies using HMRC's own online filing service (the free basic CT600 tool), which does not produce fully iXBRL-tagged accounts. HMRC has signalled that this exemption is ending and that all CT600 submissions must be accompanied by iXBRL-tagged accounts.

The timeline: HMRC published proposals for mandatory iXBRL filing for all companies, including small companies, with implementation targeted from April 2026 onwards. The exact phase-in dates are still being finalised, but the direction is clear. Companies that have been relying on HMRC's basic filing tools will need to move to iXBRL-compatible software or use an accountant who produces iXBRL-tagged accounts. For Fileminder clients, this change requires no action — our accounts-production software already generates fully iXBRL-compliant output.

Making Tax Digital for Corporation Tax (MTD CT) sits alongside this: it is HMRC's plan to bring quarterly digital reporting to corporation tax, mirroring the MTD ITSA changes happening now for income tax. A consultation was completed, but a confirmed implementation date for small companies has not yet been set as of mid-2026. When it arrives, it will require companies to submit quarterly summaries of income and expenses to HMRC digitally. The software requirement will be the same: MTD-compatible accounting tools, not manual or paper-based records.

What Arab directors should take from this: if your UK company currently files its corporation tax return and accounts through a process that involves PDF uploads, manual entry, or HMRC's free basic CT600 tool, a compliance gap is developing. The practical solution is to ensure your accountant uses iXBRL-compatible software — or to engage Fileminder, where this is already the standard. The underlying financial impact is zero: iXBRL is a format change, not a tax change. It does not change what you pay, only how the information is submitted.