Five Common Self Assessment Tax Return Mistakes
Self Assessment brings together income, expenses, tax already paid and available reliefs. Small errors can produce an incorrect bill, delay a repayment or lead to questions from HMRC.
1. Missing a Source of Income
A tax return may need to include employment, self-employment, pensions, property, savings, dividends, foreign income and capital gains. Do not assume information already held by HMRC will automatically appear correctly on the return.
Gather P60s, P45s, pension statements, bank interest certificates and other records before starting.
2. Claiming Incorrect Expenses
Business expenses must meet the relevant tax rules. Personal costs cannot be claimed simply because they were paid from a business account. Mixed-use expenses need an appropriate business calculation.
Equally, failing to claim genuine expenses can result in too much tax. Read our guide to business expenses and retain suitable evidence.
3. Forgetting Payments on Account
The amount due on 31 January can include the remaining tax for the year and the first advance payment towards the following year. A second payment may then be due on 31 July.
This often makes the first Self Assessment bill larger than expected. Our payments on account guide explains the calculation.
4. Using Estimates Without Explanation
If final information is genuinely unavailable, a provisional figure may sometimes be used, but it must be identified and corrected. Guessing figures or leaving transactions unexplained can make the return unreliable.
Good record keeping and regular bookkeeping reduce this problem.
5. Leaving Everything Until January
Online returns and tax payments are normally due by 31 January. Waiting until the deadline leaves little time to find missing documents, correct bookkeeping or query unexpected figures.
Preparing early does not bring the payment deadline forward. It tells you what will be due and gives you time to manage cash flow.
Before submitting, compare the return with HMRC records and the previous year. Large unexplained movements may be correct, but they deserve review. Keep a copy of the final return, calculation and supporting schedules so future queries can be answered consistently.
Check bank details carefully when claiming a repayment and never disclose HMRC login credentials in response to an unexpected message.
GMS Accountants prepares Self Assessment returns for individuals and sole traders in Cambridge and Nottingham. Contact us for help completing an accurate return.
