"Most iXBRL filing errors are easier to prevent before submission than to repair after rejection."
- Digital Reporting UK
Before submitting an iXBRL file to HMRC or Companies House, use this checklist to catch errors that can trigger rejection, rework and filing delays.
The checklist is designed for preparers, reviewers, accounting firms and finance teams that want a repeatable 30-minute pre-submission review.
How to use it: work through each section with the tagging file, accounts and tax return open. Keep the completed review evidence with the filing records and working papers.
Section 1: Entity and Period Validation
Company Registration Number (CRN) verified
Copy the CRN directly from Companies House lookup rather than typing it manually. Check leading zeros and exact formatting.
Example: If Companies House shows 00123456, the iXBRL file should not shorten it to 123456.
Accounting period dates match High risk
Check that the accounts period, CT600 period and iXBRL period dates match exactly.
Example: Accounts show 1 April 2025 to 31 March 2026. CT600 and iXBRL period start and end dates should match that same range.
Company name exact match
Match the Companies House registered name, including punctuation, abbreviations and capitalisation.
Example: Smith & Co. Ltd. should keep the ampersand, abbreviation and full stop where registered.
Section 2: Taxonomy Version and Software
Taxonomy version is current High risk
Confirm the tagging software is using the current FRC taxonomy for the filing period. Outdated taxonomy versions are a common rejection trigger.
Example: Open the software settings and confirm the taxonomy version before exporting the final iXBRL file.
Software updated recently
Run available software updates before filing, especially during taxonomy or HMRC gateway update windows.
Example: Check Help or About in the software and confirm update status before exporting.
Section 3: Mandatory iXBRL Fields
Profit or loss figure tagged High risk
Every filing should tag the profit or loss figure correctly. Losses should not be treated as positive profit values.
Example: A loss of £50,000 should be represented as a negative value in the tagging output.
Total assets and liabilities tagged High risk
Balance sheet totals should be tagged and should reconcile to the accounts.
Example: Total assets and total liabilities plus equity should agree before submission.
Audit statement tagged where applicable
If the company had an audit, check that the audit opinion or audit status is tagged appropriately.
Example: If not audited, confirm the relevant audit exemption or not-required status is correctly handled.
Section 4: High-Risk Item Spot Check
Related-party transactions reviewed High risk
Search for related-party or director transactions and confirm the tag choice is reasonable and documented.
Example: Keep a short decision note for judgement-heavy related-party balances and disclosures.
Contingent liabilities identified High risk
Contingencies, guarantees, lawsuits and legal claims often require judgement between provision and disclosure tagging.
Example: Record why the item was tagged as a provision or contingency disclosure.
Deferred tax and provisions reviewed High risk
Deferred tax and provisions involve estimates. Confirm amounts, signs and tags align with the accounts narrative.
Example: Compare tagged deferred tax balances to the note disclosure and tax working papers.
Section 5: Pre-Submission Validation
HMRC test gateway validation passed
Use available HMRC test or validation routes before final submission and resolve errors before deadline pressure builds.
Example: Export, validate, fix errors and repeat until the validation report is clean or all warnings are documented.
Internal quality spot-check completed
Pick 10 random line items from the accounts and verify each tag, value, sign and period.
Example: Check salaries, rent, depreciation, tax, debtors, creditors and other common accounts lines.
File size and format verified
Confirm the file is in the expected iXBRL HTML format and is within filing size limits.
Example: Check the exported filename, extension and file properties before upload.
Section 6: Sign-Off and Record Keeping
Partner or manager sign-off documented
Have a competent reviewer sign off the checklist before final submission and keep the evidence with the working papers.
Example: Retain the checklist, validation report, iXBRL file, decision log and filing confirmation together.
Five Common iXBRL Mistakes to Avoid
- CRN formatting: manual typing creates avoidable errors. Copy from Companies House.
- Period date mismatches: use one source of truth for accounts, CT600 and iXBRL dates.
- Outdated taxonomy: update software before filing season and again before final export.
- Loss tagged as a positive number: check signs for profit, loss, reserves and contra balances.
- No pre-submission validation: do not leave validation until the filing deadline.
Helpful Notes for Reviewers
Audit trail: document judgement calls, especially related parties, contingencies, deferred tax and unusual provisions.
Rejection turnaround: if a filing is rejected, allow time to review the error report, correct the file and resubmit.
Deadline risk: if the deadline is close, validation becomes more important, not less. A rejected last-minute file can create penalty exposure.
Vendor transparency: if tagging is outsourced, ask for a decision log, exception report or review summary that can be retained with working papers.
Get Professional iXBRL Validation
Digital Reporting (UK) can review your iXBRL file before submission, check high-risk tags, run validation checks and provide a clear issue list for correction.
Schedule a Validation Review