UK tax tools · source checked
Identify the step that failed before changing the figures. This list links each problem to the relevant HMRC guidance.
Where it appears: A return page or deadline belongs to a different year.
What to check: Check the year in the account and the period covered by the income. The January 2027 deadline normally covers 2025/26, not current-year income. Open the matching return.
Where it appears: Registration is incomplete or the record cannot be found.
What to check: Check your Personal Tax Account, HMRC app and previous correspondence. Use HMRC’s response-time service if registration is still processing; avoid creating a duplicate record.
Where it appears: An old UTR exists but online filing is not available.
What to check: Use the registration service to check whether reactivation is required. A previous registration does not establish that the account is active for the selected year.
Where it appears: A salary entry and its tax deduction do not match the P60 or P45.
What to check: Compare each employment record with the relevant certificate. Keep gross pay and tax deducted in the right fields; do not report net pay as gross employment income. Use the return’s help text for that section.
Where it appears: The trading-income threshold is checked after expenses.
What to check: Test gross trading receipts first. Work out profit separately for the return, and do not deduct both the trading allowance and the same expenses.
Where it appears: Gross rent, net profit and an allowance are mixed together.
What to check: Separate rent received from allowable expenses and finance costs. Check whether the property allowance is available before using it. Different reliefs and joint ownership need separate consideration.
Where it appears: The submitted figures need correction.
What to check: For online returns, wait the stated processing period, select the correct year in the account and file the amended return. Outside the amendment window, use HMRC’s written correction route.
Where it appears: The account will not open or filing fails before confirmation.
What to check: Use the technical support route linked in HMRC’s help guide. Keep the displayed error and time. A saved draft is not a submission confirmation.
Ordinary amendments can be made within 12 months of the Self Assessment deadline. HMRC says to wait 72 hours after online filing before amending. Older errors and some claims have different routes. Read the correction steps and deadlines.
For a technical error, use online-service technical support. For a filing requirement, registration or tax question, use general Self Assessment enquiries. If personal circumstances make contact difficult, HMRC’s extra-support route is linked in the same guide. Choose the right support route.
This situation is outside this checker’s scope. Consult an ATT or CTA-qualified tax adviser for an individual review. Read HMRC’s guidance on choosing an adviser and use the CIOT Find a Member directory.
No. Check for submission confirmation in the HMRC service.
Use the correction guide; outside the ordinary amendment window HMRC requires a written route.