How to avoid self-assessment deadline panic

Have you left sorting out your self assessment tax return until the last minute, despite promising yourself that you wouldn’t do it again? Tut, tut! The online filing deadline, which is midnight on 31 January, is now fast approaching and you’re probably beginning to panic.

First things first: stop panicking. No good ever comes from panicking. Instead, take control of the situation. We’re about to share the steps you can take today to get your self assessment tax return done and dusted quickly and with minimum fuss, so you can get on with other things.

Step 1: Gather the information you need

Obviously, you should already be registered for self assessment. If not, visit GOV.UK to find out how to register for self assessment.

If you don’t have everything to hand that you need to complete your self assessment tax return, getting it together before you start will speed things up considerably. You will need:

• Your ten-digit UTR (ie Unique Taxpayer Reference) number. This enables HMRC to identify you as a taxpayer. It will be printed in previous tax returns and tax letters that HMRC has sent you.
• Your National Insurance number (you’ll find it in your Personal Tax Account, previous payslips, P60s, personal tax letters, etc).
• Details of all UK taxable income you received within the tax year. This could come from self-employment, employment, rental income, share dividends, pensions, savings interest, state benefits, capital gains from the sale of taxable assets, tips and commission, etc.
• Details of all tax expenses for which you wish to claim tax relief.
• Details of pension scheme payments you’ve made during the tax year.

Step 2: Know which supplementary pages you must complete

As well as the SA100 (the main self assessment tax return), you may need to complete the following supplementary pages:

• Sole traders must complete the SA103 self employment supplementary pages.
• Those with taxable UK rental income must complete SA105.
• Those with non-UK income or gains must be reported via an SA106.
• Those who have made a capital gain after selling an asset need to complete SA108.

Visit GOV.UK for a full list of self assessment tax return supplementary pages.

Step 3: Use self assessment tax return-filing software

You can complete and file your self assessment tax return online. You sign in using your Government Gateway user ID and password.

HMRC publishes online guidance notes on completing your tax return but having to stop to read up every time you need to fill in part of your tax return makes the process slow and laborious. Plus, if you don’t understand something, there’s nothing to prevent you from making mistakes that later cost you time and money.

For speed and added peace of mind, many people use commercial tax return filing software. It prevents simple mistakes and saves a lot of time and hassle when you’re completing your self assessment tax returns. If you use accounting software, key numbers can be quickly pulled through into the right places within the tax return filing software, with the necessary supplementary pages also added once you specify your sources of taxable income. The software holds your hand through the process, with automatic prompts helping to prevent basic mistakes.

An annual subscription for decent tax return filing software can cost less than £60 a year, which is much less than paying an accountant to fill in and file your tax return (and you’ll still have to gather together all of the information the accountant needs).

Step 4: Pick the right day, time and place

Set aside a morning or afternoon to complete your self assessment tax return. Make it a day when you’re less busy with other things. Also pick a place that’s quiet and free from distractions, where you can focus on the job in hand. If possible, avoid doing it at night when you’re feeling more tired, because it will take longer and there’s a greater chance that you’ll make a mistake. If other people are around, make sure they do not disturb you so you can concentrate on completing your tax return.

Step 5: Complete your tax return in one sitting

Commit to getting your tax return done in one sitting, because that should mean you get it done in less time. Ignore your emails, messages and calls. Make yourself a nice cuppa, relax and work methodically through your tax return and supplementary pages.

Allow about three hours to get the job done if you’ve first gathered together all of the information you need. You may do it quicker, especially if you use self assessment tax return filing software – but don’t rush. Get it right the first time. Keep on going, don’t stop and don’t allow yourself to become distracted. When completed, leave yourself enough time to quickly check through your tax return at the end, just to make sure you haven’t left anything out.

Next time

In future, try to avoid leaving it so late. You can file your self assessment tax return any time after the UK tax year ends on 5 April. That way, you will know exactly what you owe, and you can start saving ready to pay the bill by 31 January.

If you’re not already doing so, using accounting software to record your income and expenses really makes it much easier to get the summary figures you need for your tax return. For now, good luck with getting this year’s self assessment tax return off your plate.

Copyright 2025. Sponsored post by Mike Parkes of GoSimpleTax - tax return software that can help you manage your self assessment.