PERSONAL TAX
Self Assessment deadlines to prepare for this autumn
September 2026
TJB Accountants | September 2026
September is a good time to check whether you need a Self Assessment return for 2025/26. The deadline to tell HMRC that you need to file is 5 October 2026 if you are new to Self Assessment or need to restart after not filing for 2024/25.
Registration and filing are separate steps. Leaving registration until January can delay the preparation of your return, even though the usual online filing deadline is later.
Check whether you need a return
A return is generally required if you were a sole trader with gross trading income above £1,000 in 2025/26 or were a partner in a business partnership. Other reasons can include taxable capital gains or the High Income Child Benefit Charge where it is not paid through PAYE.
Untaxed rental income, dividends, savings interest and overseas income may also create a filing requirement. The amount and circumstances matter, so use HMRC’s checking tool or ask your accountant rather than assuming every receipt requires registration.
Having tax deducted from a salary does not necessarily cover your other income. Review the full year’s position, particularly if you started a side business, let a property or received investment income.
Register or reactivate by 5 October
If you need a return and have not filed before, register using the appropriate route for your circumstances. If you already have a Unique Taxpayer Reference, you may need to reactivate your existing record instead of creating a new registration.
Provide your accountant with any existing UTR and HMRC correspondence. Confirm who is completing registration and keep the acknowledgement with your records.
Understand the filing and payment dates
For most 2025/26 returns, the paper filing deadline is 31 October 2026. The usual online filing deadline is 31 January 2027, which is also the deadline for paying the tax due.
If you want an eligible Self Assessment bill collected through your PAYE tax code, the online return normally needs to be submitted by 30 December 2026. Eligibility conditions still apply.
Registering after 5 October can result in a later filing deadline notified by HMRC, but it does not move the usual 31 January payment deadline. Do not treat late registration as extra time to fund the bill.
Gather your records before the winter rush
- P60s, P45s and details of taxable employment benefits.
- Business income, expense records and any CIS deduction statements.
- Rental income and property expense records.
- Dividend, interest and overseas income statements.
- Details of pension contributions, Gift Aid and Child Benefit where relevant.
- Records of asset disposals and tax payments already made.
Use an early return to plan ahead
Preparing the return early gives you time to resolve missing information and discuss the amount to set aside. It also allows you to review any payments on account alongside the final liability.
Keep a separate tax reserve and review it against the estimate your accountant provides. A completed return is more useful for cash planning than a rough percentage of income that has not been checked against your circumstances.
Tell us about changes during the year
Mention a new trade, a property purchase or sale, changes to employment and any substantial change in income. A short note explaining what changed can help identify records that would otherwise be overlooked.
If HMRC has issued a notice to file but you believe no return is needed, ask for the position to be reviewed. Do not simply ignore the notice.
Need help?
TJB Accountants can help you understand how these developments affect you and make sure the right records, registrations and filings are in place.
Official sources
- GOV.UK Self Assessment deadlines
- GOV.UK guidance on who must send a return
- GOV.UK registration and reactivation guidance
Disclaimer: This article provides general information only and does not constitute advice tailored to your individual circumstances. Information is correct as at 30 September 2026.
