iXBRL Tagging

Every UK company must attach iXBRL-tagged accounts and computations to its corporation tax return, and Companies House increasingly expects digitally tagged filings too. Get the tagging wrong and returns bounce, deadlines slip and HMRC's risk systems take a closer interest in your company. Our team tags, validates and files accounts every week — whether we prepared them or your own team did — so your submissions land cleanly, first time.

What is iXBRL and Why It Matters

iXBRL (Inline eXtensible Business Reporting Language) embeds machine-readable tags inside human-readable accounts, letting HMRC and Companies House process filings automatically. HMRC requires the accounts and tax computations attached to every CT600 to be iXBRL-tagged against the current taxonomies. Poor tagging has real consequences: rejected submissions close to deadlines, penalties for late returns, and mis-tagged figures feeding HMRC's automated risk profiling. Accurate tagging is not a formality — it is part of presenting your company correctly to the tax authority.

Our iXBRL Services

- Full iXBRL tagging of statutory accounts under FRS 105, FRS 102 (including Section 1A) and IFRS - Tagging of corporation tax computations for the CT600 - Managed tagging of accounts prepared by your own finance team or another firm - Validation against HMRC and Companies House rules before submission - Quality assurance review of every tag by experienced accounts staff, not just software - Electronic submission to HMRC and Companies House, with confirmations retained for your records

How the Process Works

Our five-step process keeps tagging fast and reliable: 1. Receive your finalised accounts and computations in Word, Excel, PDF or direct from accounting software 2. Apply iXBRL tags against the current UK taxonomies 3. Run automated validation against HMRC and Companies House business rules 4. Human quality assurance review of judgement tags — the ones software gets wrong 5. Submit electronically and confirm acceptance to you

Because tagging is standardised, turnaround is quick — and urgent pre-deadline jobs are our speciality.

Deadlines and Digital Filing Changes

Your CT600 with iXBRL attachments is due 12 months after the end of the accounting period, and Companies House accounts 9 months after year end for private companies. Companies House had planned to mandate software-only filing from April 2027 under its transparency reforms; that timetable was paused in January 2026 and remains under review, with at least 21 months' notice promised before changes. Whatever the final rules, our filings are already fully digital — so nothing will change for you.

What You Get With Acumon

• iXBRL tagging for FRS 105, FRS 102, Section 1A and IFRS accounts
• Tagging of accounts prepared by us, your team or another firm
• Automated validation plus human review of judgement tags
• Electronic submission to HMRC and Companies House with confirmations
• Fast turnaround, including urgent pre-deadline work
• Seamless integration with our accounts and corporation tax services

Why Acumon for iXBRL Tagging?

• ICAEW-registered firm of chartered accountants
• UK-based team of 90+ staff tagging and filing accounts every week
• Human quality assurance on every submission, not just software validation
• Integrated accounts and corporation tax teams, so filings always agree

Get a Fixed-Fee Quote

Tell us what you need and we'll come back within one business day with a clear scope and a fixed price — no hourly-rate surprises. Call 020 8567 3451 or use the form and we'll be in touch.