1. Build a gap register rather than waiting for everything
List each missing item, the relevant income source, tax year, provider, recovery request date and next action. Record whether it affects income, an expense, a relief or tax already deducted. Separate unavailable evidence from a genuine dispute about tax treatment.
For example, a missing rental-agent statement needs a statement request and reconciliation. An uncertain repair-versus-improvement classification needs the invoice and a technical review. The remedies are different.
2. Request duplicates and reconcile independent records
Ask banks and suppliers for duplicate statements and invoices. Request payroll documents from the employer and transaction histories from agents or investment providers. Preserve the original exports before editing a working copy.
Match receipts to invoices and explain transfers, loans and reimbursements rather than treating every bank credit as income. For investments, a sale receipt alone does not establish the acquisition cost. Use our investment records guide where relevant.
3. Distinguish provisional figures from estimates
A provisional figure is temporary: you expect to obtain evidence and provide the final figure later. An estimated figure is intended as the final figure because an accurate amount cannot be established. HMRC distinguishes the two, so do not label every missing document as provisional.
First make reasonable recovery efforts. Retain your method, evidence, assumptions and calculations for any remaining figure. An unsupported round number is not a substitute for reconstruction, and labelling a figure does not make an otherwise incomplete return acceptable.
4. Explain the position on the return
HMRC guidance requires an explanation in the return’s additional-information section where provisional or estimated figures are used. For provisional figures, identify what remains outstanding, why, the method used and when final information is expected. Follow the current form or software instructions for the provisional-figures indicator; HMRC says estimated final figures do not require that indicator solely because they are estimated.
Have your adviser review the wording alongside the calculation. Disclosure does not guarantee protection from interest or penalties if the figures are wrong.
5. Keep filing, payment and correction dates separate
The normal online deadline for 2025/26 is 31 January 2027. Check any specific HMRC notice. Missing information does not itself extend the filing or payment date. Where provisional figures are appropriate, track the final evidence and amend the return promptly when it arrives. HMRC normally permits amendment within 12 months of the Self Assessment deadline.
If final figures increase the tax, interest can run from the original payment due date. Reconcile the revised liability and payments on account. Read our corrections guide for the evidence process, noting that its worked deadline concerns an earlier tax year.
Get the reconstruction scoped early
Tell us the income sources, missing documents, affected years and any HMRC contact. We can assess the recovery work and agree a realistic scope before requesting confidential records. Reconstruction, earlier-year corrections and disclosures may require work beyond a routine return.
Personal tax services start from £400. UA Tax supports clients in London and across the UK. Get in touch for a scoped quote. General guidance cannot determine whether your particular return is ready to file.
For advice on your own circumstances, see our return preparation with missing records service and agree the scope before acting.
Official sources and further reading
These primary sources support the framework above. Check the current version before acting because tax law and HMRC guidance can change.