Start with the filing obligation
Self Assessment taxpayers must determine whether they need to file for the relevant tax year and whether they are using an online or paper return. The official 2026 tax-return form states that a paper return is due by 31 October 2026, while online filing follows the later statutory deadline shown by HMRC for the relevant return cycle. Taxpayers should not wait until the deadline to register, gather records or calculate tax because registration and filing are separate compliance steps.
Records to assemble
A practical compliance file should include:
- Employment income records, including P60s and P11Ds where relevant;
- Dividend vouchers and company resolutions;
- Bank and investment statements;
- Property-income schedules and allowable expense evidence;
- Pension contribution and Gift Aid records;
- Foreign income, gains and exchange-rate calculations; and
- Contractor invoices, contracts, timesheets and working-practice evidence.
Records should be organised by tax year. A spreadsheet that reconciles bank receipts to declared income is often more useful than a collection of unlabelled PDFs.
Contractors and IR35 evidence
For contractors operating through an intermediary, tax compliance is not limited to completing the return. The parties should examine the engagement’s actual terms and working practices. Evidence may include who controls the work, whether substitution is genuinely available, how financial risk is allocated, and whether the client treats the contractor as part of its organisation.
Where the off-payroll working rules apply, the responsible party may need to determine status and communicate a status determination statement. A contractor should retain the determination and supporting correspondence, even where the contractor is not the party legally responsible for making it.
Avoid common deadline failures
File early enough to resolve authentication, missing documents or HMRC queries. Check whether a payment on account is due, and do not assume that a previous year’s liability predicts the current year. If an amendment is required, document why it was made and retain the original calculation.
The safest approach is a recurring quarterly review: reconcile income, update estimated tax, check documentation and flag changes in residence, employment status or business structure before year-end.