Why September is the best time to start your Self Assessment Tax Return
If you’re a sole trader, landlord, or an individual with extra income, your Self Assessment tax return is probably sitting at the bottom of your to-do list. After all, the online filing deadline isn’t until 31 January. Plenty of time, right?
It’s easy to keep putting it off when January feels so far away. But getting started in September gives you plenty of time to gather your paperwork, ask questions if you’re unsure about anything and avoid a last-minute scramble.
Whether this is your first Self Assessment return or you’ve been filing for years, starting in September can make the entire process simpler and give you greater control over your finances.
Why September is the right time to get started
By the time September arrives, the tax year that finished on 5 April already feels like a while ago. Most people have received any bank interest information they need, and you’ll probably have a much better idea of what you’ve earned and what you’ve spent.
Getting started now is far easier than leaving everything until December or January, when work, holidays and family commitments often take over.
It also gives you time to deal with anything unexpected. If paperwork is missing or you need extra information, you’ll have weeks rather than days to get everything sorted.
Key Self Assessment deadlines you shouldn't miss
One of the most common reasons people run into problems is forgetting that some deadlines arrive well before January.
HMRC says that if you’re required to register for Self Assessment for the first time, or you’re joining the system again after previously leaving it, you should normally register by 5 October following the end of the tax year. Missing that deadline can delay the process and could result in penalties.
The key dates are:
- 5 October – Registration of Self Assessment.
- 31 October – Deadline for paper tax returns.
- 30 December – Online filing deadline if you want eligible tax owed to be collected through your PAYE tax code.
- 31 January – Deadline to submit your online tax return and pay any tax due.
Starting your return in September means you’re comfortably ahead of every deadline.
Why waiting until January can cost you
Every January, accountants receive a flood of urgent calls from people who have only just started thinking about their tax return.
Common problems include:
- Missing paperwork.
- Forgotten sources of income.
- Difficulty accessing HMRC accounts.
- Waiting for information from banks or investment providers.
- Uncertainty about allowable expenses.
These issues become much more stressful when the filing deadline is only days away.
Leaving everything until January often means making rushed decisions. The more pressure you’re under, the easier it is to overlook something important.
Find out what you owe before the January deadline
One of the biggest benefits of completing your tax return early is knowing exactly what you owe.
Many people delay filing because they worry about receiving a tax bill. Ironically, waiting only gives you less time to prepare for it.
Once your return has been completed, you’ll know how much tax is due by 31 January. HMRC also encourages taxpayers to submit returns early so they can understand their tax position and budget in advance.
Filing early doesn’t mean paying early. It simply gives you a clear picture of what you’ll need to pay, making it much easier to plan ahead.
Don't miss out on valuable tax reliefs
Rushing a tax return often means overlooking valuable claims.
Depending on your circumstances, you may be able to claim allowable business expenses, property-related expenses, pension contributions, charitable donations or other reliefs.
Every taxpayer’s situation is different, which is why professional advice can make a significant difference.
Taking the time to review everything carefully means you’re less likely to overlook expenses or reliefs you’re entitled to claim.
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Why sole traders should start early
If you’re self-employed, September is an excellent time to review your bookkeeping before submitting your return.
Instead of trying to remember expenses from many months ago, you can identify any missing receipts, reconcile your accounts and ensure your records are complete.
HMRC requires taxpayers to keep accurate records to complete their Self Assessment correctly. Good record keeping also makes future tax returns much easier. The same applies if you earn income from property, where tax calculations can be more complicated than many people expect.
Worth knowing: Making Tax Digital for Income Tax (MTD for ITSA) is being introduced in stages, so self-employed people should check when the rules will apply to them.
Read more: MTD for ITSA
Why landlords shouldn't leave it until January
Property income often involves more than simply adding up rental payments.
Landlords may need to consider allowable expenses, mortgage interest rules, jointly owned properties, furnished holiday accommodation changes where applicable, capital gains implications and other property-related tax matters.
Leaving these calculations until January increases the risk of errors.
Preparing your information in September allows plenty of time to review everything accurately before submission.
A quick MTD reminder: MTD for ITSA will also affect some landlords with qualifying property income. If you receive rental income, it’s worth checking the new rules now rather than waiting until they apply.
Read more: MTD for ITSA
Common Self Assessment mistakes to avoid
Starting early helps reduce the likelihood of common errors, including:
- Forgetting to declare all taxable income.
- Claiming expenses that are not allowable.
- Missing important supporting documents.
- Using incorrect figures.
- Registering too late.
- Waiting until the filing deadline to seek professional advice.
Even small mistakes can lead to delays, HMRC enquiries or additional costs. While many of these mistakes are avoidable, they often happen when people rush their tax return or aren’t sure what HMRC expects.
Why working with an accountant makes a difference
Completing a tax return isn’t just about entering figures into HMRC’s online system. It’s about making sure everything has been reported correctly and that you’re claiming what you’re entitled to.
An accountant can check your records, answer any questions and deal with the paperwork, leaving you free to focus on your business or your day-to-day life.
Need help with your Self Assessment tax return?
If the thought of completing your Self Assessment feels overwhelming, you’re not alone. We help individuals, landlords and small business owners take care of their tax returns every year.
We’ll check everything carefully, handle the paperwork, and keep you updated from start to finish. Speak to us today and get your tax return out of the way before the deadline.
Author
Mukund is a founding member of the Affinity Associates Group and has been with the practice for nearly 40 years. After completing his degree in Accounting and Finance, he went on to qualify with both ACCA and ICAEW in 1991. Over the years, he’s built deep expertise in consultancy, tax, business development, and corporate group structures. Mukund is known for helping clients make sense of complex financial challenges and turning them into opportunities for sustainable growth.
