A Self Assessment deadline falls today, 5 October 2026, but this is not the deadline for sending your online tax return.
Instead, certain people need to tell HMRC by 5 October that they must complete Self Assessment for the 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026.
If you need to complete a return and have never sent one before, or you were previously registered but did not need to send one for 2024/25, you should act today.
Who needs to act by 5 October?
You may need to tell HMRC if, during 2025/26, you:
- were self-employed as a sole trader and had more than £1,000 in gross trading income
- became a partner in a business partnership
- had to pay Capital Gains Tax
- had to pay the High Income Child Benefit Charge and are not paying it through PAYE
- received other untaxed income that means you need to complete Self Assessment
Untaxed income can include money from renting out property or land, tips and commission, savings interest, dividends and foreign income.
HMRC has an online checker to see if you need to send a Self Assessment tax return if you are unsure.
Who doesn’t need to register today?
If you are already registered for Self Assessment and sent a return for 2024/25, you do not normally need to register again just because it is 5 October.
And if your income is dealt with through PAYE and you have no other reason to complete Self Assessment, today’s registration deadline may not affect you.
The same applies to many people making a small amount of extra money from a side hustle.
What about side hustle income?
If you made money from a side hustle during 2025/26, the important figure is £1,000.
Most people can have up to £1,000 of gross trading income in a tax year without needing to tell HMRC about it.
Gross income means the money you received before taking off expenses.
If your gross trading income was more than £1,000, you must tell HMRC. If you’re not already registered, this normally means registering for Self Assessment.
The £1,000 limit covers relevant trading income from your side hustles combined, rather than giving you a separate £1,000 allowance for every activity.
You can read the full rules on the £1,000 trading allowance on GOV.UK.
There are exceptions where someone may still choose or need to register with income of £1,000 or less, including to claim certain reliefs or benefits.
Selling things you already own is also different from trading.
HMRC says clearing out personal possessions does not usually need to be reported, while regularly buying or making things to sell for profit is more likely to count as trading.
What about landlords?
People earning money from property should check their position too.
There is a separate £1,000 property allowance. GOV.UK says landlords with gross property income above £1,000 and up to £2,500 should contact HMRC.
A Self Assessment return is required if rental income is more than £2,500 after allowable expenses or more than £10,000 before allowable expenses.
If you do not normally complete a return, GOV.UK says you need to register by 5 October following the tax year in which you received the rental income.
What should you do today?
If you have only just realised the deadline may apply to you, start with HMRC’s Self Assessment checker.
If you need to complete a return, you can then register for Self Assessment through GOV.UK.
If you were registered for Self Assessment before but did not send a return last year, you may need to reactivate your existing account instead.
You do not need to complete your full online tax return today.
What happens if you miss the 5 October deadline?
If you should have registered but miss the deadline, tell HMRC as soon as possible.
HMRC says people who register after 5 October 2026 will normally be given three months from the date of its letter or email to send their return.
Missing the 5 October registration deadline does not automatically trigger the £100 late-filing penalty. That penalty applies when a required tax return is filed late.
However, HMRC says you could face a penalty for telling them late. Any tax owed for 2025/26 must still be paid by 11:59pm on 31 January 2027.
When is the online Self Assessment deadline?
The online Self Assessment deadline for the 2025/26 tax year is 11:59pm on 31 January 2027.
Any Self Assessment tax owed must normally also be paid by then.
The earlier deadline for paper tax returns is 11:59pm on 31 October 2026.
You can check the official Self Assessment deadlines on GOV.UK.
So, if 5 October has caught you by surprise, check whether you need to register and act as soon as possible.
It does not mean your full online Self Assessment tax return has to be completed today.
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