What happens if you don’t submit a Self Assessment tax return?

The online-filing deadline for Self Assessment tax returns is the same every year – midnight on 31 January. In 2024, according to HMRC, 12,187,811 Self Assessment returns were due and 11,581,962 were filed before the deadline. That means an estimated 1.1m were late.

People miss the Self Assessment tax return online-filing deadline for many reasons. Sometimes, they simply don’t realise that they need to submit a Self Assessment tax return to report taxable income. Many miss the deadline, despite their best intentions, but they file in the days or weeks that follow. There are those who know they need to report taxable income, but don’t submit a tax return, which makes them guilty of tax evasion.

Who needs to submit a Self Assessment tax return?

You must file a Self Assessment tax return if, in the last tax year (6 April to 5 April), you:

• were a self-employed sole trader with income of more than £1,000 before claiming any tax relief/expenses
• were in an ordinary business partnership
• are a limited company director with taxable income that hasn’t been paid through Pay As You Earn
• earned total taxable income of more than £100,000
• earned taxable income from renting out property or land
• received taxable tips or commission
• earned taxable income from savings, investments or share dividend payment
• earned taxable income from overseas sources
• have capital gains tax to pay on sale of a taxable asset
• had to pay the High Income Child Benefit Charge.

Need to know! If you need to complete a tax return and have never sent one previously, you must register for Self Assessment by 5 October following the end of the tax year (5 April) during which you earned taxable income. If you’ve registered before, but didn’t send a Self Assessment tax return last year, you just need to reactivate your existing tax account.

What if you’ve missed the Self Assessment online-filing deadline?

• If you’ve missed the Self Assessment tax return filing deadline, unless you have a valid excuse (eg partner’s death, serious illness, prevented by disability, etc), there’s an automatic £100 late-filing fixed penalty – even if there’s no tax to pay or you pay any tax that’s due.
• Then, after three months, there’s a further penalty of £10 per day for up to 90 days (ie up to a maximum of £900).
• After six months, there’s a further penalty of 5% of the tax due or £300, whichever is higher. This is on top of the penalties already detailed above.
• After 12 months, another 5% or £300 is payable, whichever is higher, in addition to the previous penalties.
• If you have a valid excuse for not filing your Self Assessment tax return before the deadline, you should appeal within 30 days of your penalty notice being issued. HMRC will consider later appeals in special cases.

What if you needed to submit a Self Assessment tax return but didn’t?

If HMRC sends you a tax return, by law, you must complete and file it (or complete one online), even if you don’t owe any tax because you haven’t earned any taxable income in that tax year – unless you contact HMRC and request that the tax return be withdrawn.

If you do not file a tax return after you’ve been asked to do so, HMRC will charge you penalties. It will also send you an estimated bill (a “determination”), which you must pay. HMRC can pursue payment through the courts – even if that means making you bankrupt. The only other alternative is to fill out a tax return so that the correct amount can be calculated and paid.

Need to know! HMRC penalties for late payment can be significant, especially if you don’t act quickly. After 30 days, you’ll be charged 5% of tax unpaid. You’ll be charged another 5% of the unpaid tax after six months, then, after 12 months, there will be another 5% of the unpaid tax to pay. GOV.UK provides advice on what to do if you cannot pay your tax bill.

How to appeal a penalty for late Self Assessment filing?

If you have a reasonable excuse, you can appeal against a Self Assessment late filing penalty. Reasonable excuses include:

• Death of a partner or close relative shortly before deadline.
• Serious, life-threatening illness or unforeseen hospital stay that prevented you from completing your tax return.
• Delays caused by disability.
• Serious computer or software failure shortly before or while preparing/filing your return online.
• Serious issues with HMRC’s online services.

Need to know! Claiming that someone else failed to file your return before the deadline isn’t a valid excuse, neither is finding it hard to use HMRC’s online filing system or claiming you didn’t know when the deadline was.

If you have a valid reason, you should appeal your late-filing penalty within 30 days of your penalty notice being issued, although HMRC considers late appeals in special circumstances.

If HMRC sends you a penalty letter, you can either use the appeal form that comes with it or follow the alternative instructions explained in the letter. HMRC may ask for evidence of your claims and there are no guarantees that your appeal will be accepted.

How to avoid missing the Self Assessment deadline next year?

1. Use accounting software

Undoubtedly, using accounting software regularly to enter details of your income and any costs that you wish to claim as tax expenses will make completing your Self Assessment tax return far quicker and easier. If you’re a sole trader, it will also enable you to better understand and control your cash flow. Always make sure your figures are fully updated come the end of the month.

2. Increase your knowledge

If you struggle with any parts of the SA100 Self Assessment tax return or any supplementary pages that you need to complete and file, take time to find out what information you need to enter and where it should go.

3. Use Self Assessment filing software

Using Self Assessment filing software makes the job far easier and quicker, with mistakes less likely, too. There are many handy, time-saving shortcuts and you may even find ways to pay less tax that you weren’t aware of.

4. Fully commit to doing it earlier

You can complete and file your Self Assessment tax return as soon as the tax year ends on 5 April. You don’t have to do it on 6 April, of course, but doing it earlier, rather than waiting until January, reduces the risk that you’ll miss the deadline.

5. Set aside time long before January

Simply setting aside time in your diary (at least two or three hours if you have all of your figures to hand) long before the midnight 31 January deadline to complete your Self Assessment tax return and not letting anything affect it could make a big difference. Could be in October or November, or at a time of year when you’re less busy. To make your life much less stressful, don’t leave it until January.

GoSimpleTax is award-winning software that makes it quick and easy to complete and file your Self Assessment tax return and supplementary pages. It can also prevent you from making basic tax return errors that can later cost you time and money. Thousands of sole traders, landlords and other taxpayers love GoSimpleTax. Start your FREE trial today!

Blog content is for information purposes and over time may become outdated, although we do strive to keep it current. It's written to help you understand your Tax's and is not to be relied upon as professional accounting, tax and legal advice due to differences in everyone's circumstances. For additional help please contact our support team or HMRC.