10 min read
The 31 January deadline has a way of arriving faster than most people expect, and every year HMRC confirms that millions are still filing in the final weeks, with a significant number submitting in the closing hours of deadline day itself.
The reason usually isn’t a lack of tax knowledge. It’s time. When a return is completed under pressure, figures get estimated instead of checked and sections get skipped by accident; not because the rules aren’t understood, but because there wasn’t enough time to go back to check it. Starting your Self Assessment early removes that pressure, and with it, most of the errors that tend to cause problems later on.
Why the last minute rush causes so many errors
Self Assessment is easy to put off in September, when the deadline still feels miles away and nothing about it feels urgent. But HMRC’s figures show what happens next: as January closes in, you are suddenly at the final deadline, and that’s exactly when mistakes slip through, simply because there’s no time left to catch them.
1. Missing the registration deadline
Anyone filing for the first time, whether they’ve started freelancing, taken on rental income or set up a small business, needs to register with HMRC by 5 October following the end of the relevant tax year. This deadline is separate from the filing deadline, and it’s often overlooked because it comes so much earlier.
Miss it, and a penalty can apply before a single figure has even been submitted. Registering also takes time, since HMRC needs to issue a Unique Taxpayer Reference before a return can be filed at all, and that process can take longer than people expect.
2. Relying on estimated or incomplete figures
Anyone filing for the first time, whether they’ve started freelancing, taken on rental income or set up a small business, needs to register with HMRC by 5 October following the end of the relevant tax year. This deadline is separate from the filing deadline, and it’s often overlooked because it comes so much earlier.
Miss it, and a penalty can apply before a single figure has even been submitted. Registering also takes time, since HMRC needs to issue a Unique Taxpayer Reference before a return can be filed at all, and that process can take longer than people expect.
3. Overlooking allowable expenses and reliefs
This is one of the more expensive mistakes, because it usually means paying more tax than necessary. Returns put together in a hurry often miss legitimate claims, such as:
- Costs of working from home
- Business mileage and travel
- Professional subscriptions and training courses
- Pension contributions and Gift Aid payments, which can affect the tax band you fall into
Reviewing expenses properly takes a bit of time and a clear head, neither of which are available at eleven o’clock at night on 31 January.
4. Missing supplementary pages
Depending on individual circumstances, additional pages may need to be completed alongside the main return. This applies to people with rental income, capital gains, foreign income, or those who are company directors.
It’s a step that’s easy to miss, particularly if circumstances have changed since the last return was filed. Starting early gives enough time to check which pages actually apply, rather than discovering halfway through the process that extra information is needed and isn’t readily available.
5. Getting payments on account wrong
Anyone with a tax bill over £1,000 will usually need to make payments on account towards the following year’s liability. This catches a lot of people out, either because they haven’t budgeted for the payment or because they don’t realise it can be reduced if their income has dropped. Working this out early gives time to plan properly, rather than being surprised by a bill that’s larger than expected.
6. Incorrect bank or personal details
It sounds like a minor point, but errors in bank details, National Insurance numbers or UTRs are a common cause of delay, particularly where a refund is due. A quick check when there’s no pressure catches these long before they become a genuine problem.
7. Leaving no time to pay
Filing a return and paying the tax owed are two different tasks, and both need to be done by 31 January. Filing early means knowing the amount owed well in advance, which leaves time to set money aside, or if needed, to arrange a Time to Pay agreement with HMRC before the deadline rather than after penalties and interest have already started to build up.
What starting early actually gives you
None of this means filing the return the day the new tax year begins. It simply means giving the process enough room to breathe. With more time, it becomes possible to:
- Chase missing information from clients or a bank while there’s still time to get it
- Spot and correct errors calmly, without the pressure of a looming deadline
- Plan properly for a tax bill instead of scrambling to find the money
- Avoid the automatic £100 late filing penalty, which applies even where no tax is actually owed
HMRC continues to encourage taxpayers to file well ahead of the January deadline, and the reasoning is straightforward. Early filers make fewer mistakes, largely because they aren’t working against the clock.
How Golding can help
Self Assessment doesn’t need to turn into a January scramble every year. At Golding, we work with individuals and businesses throughout the year, not just in the weeks before the deadline, so figures are accurate, allowable expenses are properly claimed, and nothing is left to the last minute. If you’d like some support getting ahead of this year’s return, get in touch with our team and we’ll take the pressure off.
Anthony Burrell is the Tax Director at Golding Accountancy, specialising in UK personal tax, compliance, and strategic tax planning. He works with business owners, landlords, and property investors across the UK, helping them navigate complex tax legislation while ensuring they remain compliant and tax-efficient. Outside the office, Anthony is a dedicated West Ham supporter and has been a season ticket holder for more than 40 years. He also recommends Dext to clients looking to simplify their bookkeeping and financial processes.
