How to File Your Self Assessment Tax Return with Confidence: Part 2

In Part 1 of our Self Assessment series, we covered who needs to file and what to prepare before you start.

Now, in Part 2, we take you through the step-by-step process of completing your return online, how to avoid costly mistakes, and which reliefs and allowances can reduce your tax bill.

 

Step-by-Step: Completing Your Return Online

1. Check Access – Ensure you can log in to your Government Gateway and have your Unique Taxpayer Reference (UTR) handy.
2. Start Early – You can file from 6 April onward. Early filing helps with cash flow and reduces the risk of mistakes.
3. Complete the Main Form (SA100) – Add any relevant supplementary pages (SA103 for self-employment, SA105 for property income, SA108 for capital gains, etc.).
4. Enter Income Carefully
   • Savings interest: Enter the gross amount; HMRC will apply the personal savings allowance.
   • Dividends: Enter all dividends received; the allowance is £500, with rates at 8.75%, 33.75%, and 39.35%.
   • Pensions and Gift Aid: Enter gross amounts to ensure higher-rate relief is applied correctly.
5. Review Payments on Account – Check whether HMRC expects advance payments toward next year’s bill.
6. Submit and Pay – The deadline for both is 31 January 2026. If you can’t pay in full, explore HMRC’s Time to Pay arrangement.

 

Avoiding Penalties and Interest

Missing deadlines can be costly:

• Late filing: £100 fixed penalty, then £10 per day after 3 months (up to £900)
• Late payment: 5% penalty at 30 days, 6 months, and 12 months, plus 8.00% interest

Tip: Even if you can’t pay, file your return on time to avoid additional late filing penalties.

 

Payments on Account: Plan Ahead

If you owe more than £1,000 and less than 80% of your tax is collected through PAYE, HMRC may require two payments on account — due on 31 January and 31 July.

If you expect lower income next year, you can request a reduction (using form SA303 or online), but underestimating can lead to interest charges.

 

Reliefs and Allowances Often Missed

• Trading and Property Allowances: £1,000 each; choose between allowance or actual expenses.
• Rent-a-Room Scheme: Up to £7,500 tax-free income for renting a room in your home.
• Pension Contributions: Claim higher-rate relief through your return.
• Gift Aid Donations: Claim additional tax relief on top of the 25% the charity receives.
• Capital Gains: Use your £3,000 annual exemption and ensure correct rates for 2025/26.

 

Common Pitfalls

• Forgetting small amounts of interest or dividends
• Using the wrong student loan plan type
• Missing higher-rate pension or Gift Aid reliefs
• Failing to plan for payments on account

 

Final Thoughts

Filing your tax return doesn’t have to be stressful. By starting early, staying organised, and using available reliefs, you can file with confidence — and possibly save money.

If you’d like a review of your draft return or professional help preparing and filing, we’re here to help ensure your Self Assessment is accurate, compliant, and on time. Get in touch!

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