Why You Should Do Your Self Assessment in October — Not January
The online Self Assessment deadline for the 2025/26 tax year is not until 31 January 2027.
That does not mean January is the best time to complete it.
HMRC allows you to submit your return any time after the end of the tax year. Filing in October gives you more time to check the figures, deal with missing information and, most importantly, find out how much tax you actually owe. GOV.UK
For many taxpayers, getting the return completed now can turn January from a stressful tax deadline into simply a payment date.
You can already submit your 2025/26 return
The tax year ended on 5 April 2026, so there is no requirement to wait until January.
For most online returns, you have from 6 April 2026 until 11:59pm on 31 January 2027 to submit. GOV.UK
That gives you a choice.
You could wait until the final few weeks.
Or you could use October to get everything organised while there are still several months available to resolve problems.
Filing early does not mean paying early
This is one of the most important misconceptions about completing Self Assessment early.
If you submit your return in October, you do not normally have to pay the tax immediately.
HMRC specifically states that filing early does not mean you have to pay early. The normal payment deadline for the 2025/26 Self Assessment bill remains 31 January 2027. GOV.UK
So you could complete your return in October, know exactly what you owe and still have roughly three months to prepare the money.
You find out what your tax bill actually is
Imagine waiting until 25 January to complete your return and discovering you owe considerably more tax than expected.
You now have days to find the money.
Complete the same return in October and the situation is completely different.
You know the amount well in advance.
That gives you time to:
- Review your cash position
- Set money aside
- Adjust personal spending
- Plan business withdrawals
- Make regular payments towards the bill
- Speak to HMRC if you anticipate difficulty paying
HMRC explicitly recommends early filing because it allows taxpayers to establish what they owe and budget before the payment deadline. GOV.UK
Payments on account can catch people out
One reason a first substantial Self Assessment bill can come as a surprise is payments on account.
These are advance payments towards your next Self Assessment bill.
They are normally required unless either your previous Self Assessment tax bill was below £1,000 or more than 80% of the relevant tax was collected outside Self Assessment. GOV.UK
This can mean your January payment is not simply the remaining tax for 2025/26.
Depending on your circumstances, it may also include the first payment on account towards 2026/27.
Finding that out in October is much easier to manage than discovering it immediately before the payment deadline.
You have time to find missing documents
Tax returns are rarely difficult because someone cannot find a calculator.
They’re difficult because information is missing.
You might realise you don’t have:
- A P60
- A P45
- Bank interest information
- Dividend records
- Rental statements
- Business expense records
- Pension contribution information
- Investment records
- Foreign income information
- Details of a capital disposal
If you’re preparing your return in October, there is time to obtain replacements.
If you’re doing it on 30 January, missing information becomes considerably more stressful.
HMRC advises taxpayers to gather the records they need before completing their return, including information about income, expenses and tax already paid. GOV.UK
You have time to sort out your bookkeeping
For sole traders and landlords, the tax return is often only as straightforward as the underlying records.
Perhaps you discover:
- Transactions haven’t been categorised
- Personal spending is mixed with business spending
- Invoices are missing
- Bank transactions haven’t been reconciled
- Expenses were paid personally
- Income came through multiple platforms
- Your bookkeeping software doesn’t agree with the bank
These problems are much easier to resolve with three months available.
Rushing through them immediately before the deadline increases the risk of something being overlooked.
Your accountant has more time to ask questions
If an accountant prepares your Self Assessment, sending everything in January can create another problem.
They may need additional information from you.
For example:
What was this £2,400 payment?
Was this journey business or personal?
Did you receive any dividends?
Did you make personal pension contributions?
Was this property occupied throughout the year?
Those questions can materially affect the return.
Starting in October gives both you and your accountant time to establish the correct answer rather than rushing to meet a deadline.
You have more time to spot mistakes
HMRC specifically identifies having more time to check information and correct mistakes as one of the benefits of early filing. GOV.UK
That matters because a Self Assessment return can bring together several different sources of income.
You might have:
Employment + self-employment + dividends + savings interest + property income
A mistake in any one of those areas could affect the final calculation.
Getting the return completed early gives you time to review whether the figures make sense.
You can correct a return after submitting it
Submitting your return does not necessarily make it impossible to fix an error later.
HMRC says taxpayers can normally amend a Self Assessment return within 12 months of the Self Assessment deadline. GOV.UK
So filing early doesn’t mean you lose the ability to correct something if new information subsequently comes to light.
The objective should still be to make the original return as accurate as possible.
You could receive a tax refund sooner
Not every Self Assessment ends with additional tax to pay.
Sometimes you’ve paid too much tax.
HMRC specifically lists receiving a refund sooner as one of the potential advantages of submitting a return early. GOV.UK
Waiting until January simply delays the point at which the return can be processed.
If you think you may be due money back, there is little benefit in waiting purely because the filing deadline is months away.
Your completed return can provide proof of income
This can be particularly relevant to self-employed people.
HMRC notes that a processed tax return can potentially be used as evidence of income for purposes such as:
- Mortgage applications
- Loan applications
- Certain benefit claims GOV.UK
If you’re expecting to apply for a mortgage or finance, getting your latest tax affairs completed could therefore have practical benefits beyond simply satisfying HMRC.
You avoid the January rush
January is predictable.
Thousands of taxpayers realise the deadline is approaching at roughly the same time.
Accountants become busy.
People start searching for documents.
Questions need answering.
Tax needs calculating.
HMRC needs contacting.
And everything has to happen before 31 January.
Completing the work in October removes much of that pressure.
HMRC itself encourages taxpayers to file early rather than waiting until January. GOV.UK
You still have time to plan how you’ll pay
Once you know your liability, you can start planning.
HMRC says taxpayers can make weekly or monthly payments towards their next Self Assessment bill to help with budgeting. GOV.UK
For example, imagine you complete your return and discover that £6,000 will be due in January.
That information is useful.
Instead of discovering the bill days before payment, you can start considering how that £6,000 will be funded.
The tax hasn’t changed.
Your ability to plan for it has.
What if you already know you won’t be able to pay?
Completing the return early becomes even more useful.
HMRC says early filing gives taxpayers time to consider a payment plan if they do not think they will be able to pay on time. GOV.UK
Ignoring the return because you’re worried about the bill is unlikely to improve the situation.
First establish exactly what you owe.
Then deal with the payment issue separately.
Don’t rush purely to file early
There is an important distinction between:
filing early
and
filing before you’re ready.
Early filing is useful when you have the information required to prepare an accurate return.
It does not mean guessing missing figures simply to get the return submitted in October.
If important information is outstanding, use the additional time to obtain it.
Accuracy remains more important than being able to say your return was filed particularly early.
What should you do this October?
If your 2025/26 Self Assessment is still outstanding, October is a sensible month to get it moving.
Start by gathering the information relevant to you:
- Employment records
- Business accounts
- Income records
- Expense receipts
- Property information
- Savings interest
- Dividend statements
- Investment records
- Pension contributions
- Gift Aid donations
- Foreign income
- Capital gains information
Then identify anything missing.
If your accountant is preparing the return, send the information across rather than waiting until January.
Don’t forget the paper deadline
There is another reason October matters.
If you’re submitting a paper Self Assessment return, HMRC must receive it by 11:59pm on 31 October 2026.
The later 31 January 2027 filing deadline applies to online returns. GOV.UK
If you normally file on paper, October is therefore not simply an opportunity to get ahead.
It contains your actual filing deadline.
What if you’re using Making Tax Digital for Income Tax?
Making Tax Digital for Income Tax began affecting qualifying taxpayers from April 2026.
HMRC confirms that taxpayers using MTD for Income Tax still need to complete and submit their tax return through compatible software. For the 2025/26 year, the relevant return can be submitted from 6 April 2026 to 31 January 2027. GOV.UK
So being within MTD does not make the January Self Assessment deadline irrelevant.
Frequently Asked Questions
Can I submit my 2025/26 tax return now?
Yes. HMRC allows the 2025/26 return to be submitted before the January deadline. GOV.UK
If I file in October, do I have to pay immediately?
Normally, no. Filing early does not itself bring forward the standard 31 January 2027 payment deadline. GOV.UK
When is the online Self Assessment deadline?
The normal online deadline for the 2025/26 return is 11:59pm on 31 January 2027. GOV.UK
When is the paper Self Assessment deadline?
HMRC must normally receive a 2025/26 paper return by 11:59pm on 31 October 2026. GOV.UK
Why bother filing early if the deadline isn’t until January?
It allows you to establish what you owe earlier, budget for the payment, resolve missing information and reduce the pressure of completing everything immediately before the deadline. HMRC actively identifies these as advantages of early filing. GOV.UK
Can I change my return if I notice a mistake?
Yes. HMRC generally allows you to amend a submitted Self Assessment return within 12 months of the filing deadline. GOV.UK
Final thoughts
The 31 January 2027 deadline is the latest point most taxpayers should be thinking about — not necessarily the date they should be aiming for.
Completing your Self Assessment in October gives you something valuable:
time.
Time to find missing information, check the figures, understand your tax bill and make sure the money is available when payment becomes due.
At Merranti Accounting, we can prepare your Self Assessment return, review the relevant income and expenses and help you understand your tax position well before January arrives.
Written by Jenny Seaford ACPA
Senior Accountant, Merranti Accounting
Jenny is a Senior Accountant at Merranti Accounting, supporting individuals and businesses with their accounting and tax requirements. She helps clients maintain clear financial information, understand their obligations and make informed decisions based on accurate figures.
