Ahead of the 2024/25 online self-assessment (SA) filing and payment deadline of Saturday 31 January 2026, key information and reminders are set out below. Members are also advised to contact the Institute by email if they experience any issues in the coming weeks which prevent the filing of 2024/25 SA returns before the deadline so that we can discuss with HMRC. To the extent unforeseen events arise, we may be able to engage directly with HMRC to seek appropriate accommodations (in a similar manner as last year when various storms affected members).
Ahead of this year’s filing deadline, more than 4,600 festive filers escaped the turkey and tinsel on Christmas Day to file their returns with 1-1.59pm being the busiest time; maybe the brussel sprouts were on to boil? Almost 10,500 then boxed clever to file on Boxing Day. However, as at 5 January 2026, almost 5.65 million returns were still due to be filed.
By way of reminder, in November HMRC published its top SA filing tips for agents in Agent Update 137. Taxpayers should also be aware of the actions they may need to take due to the in-year changes from 30 October 2024 to the rates of capital gains tax (CGT).
Due to this mid-year change, HMRC's online SA filing software does not automatically calculate gains at the correct rates if a taxpayer has gains both before and after the changes. This software has not been updated and defaults to the lower pre-30 October 2024 CGT rates for all gains.
If a taxpayer made disposals of non-residential property assets on or after 30 October 2024, the following actions need to be taken:
- Calculate the CGT adjustment amount: the taxpayer will need to calculate the difference between the CGT due at the new (higher) rate(s) and the amount calculated by the HMRC software.
- Use the HMRC calculator to work out the CGT adjustment amount: HMRC has provided an online calculator to help individuals work out the CGT adjustment amount.
- Enter the CGT adjustment amount on the 2024/25 SA return: the resulting CGT adjustment figure needs to be manually entered into box 51 (adjustments to Capital Gains Tax) on page CG4 of the Capital Gains summary pages (SA108) of the SA return, and
- Attach the online calculator calculation: it is also recommended that taxpayers save the results page from the online calculator and submit this as an attachment with their SA return.
Key messages for the SA deadline and materials can be found on HMRC’s Frontify platform.
As this year’s filing deadline falls on a Saturday, HMRC has also sent the below message setting out details of their support arrangements on that day. This essentially means that there will be no support via telephone on 31 January, except for a call-back service for vulnerable taxpayers. HMRC has also explained below why it is taking this approach.
“What we will offer on Saturday 31 January:
- Significantly enhanced webchat capacity – approximately 200 advisers, compared to our usual Saturday staffing of around 20. This represents a ten-fold increase in capacity.
- Broader service coverage – webchat will be available across Self Assessment, the Agent Dedicated Line, Extra Support Team, Bereavement, and the Online Services Helpdesk. This is a wider range of services than we could viably staff via phone lines on a Saturday.
- A callback process for vulnerable customers needing Extra Support or Complex Case team assistance.
- 24/7 digital resources – our digital assistant and comprehensive GOV.UK guidance will remain available throughout.
Why we have taken this approach:
We have concluded that the best way to support customers is to prioritise adviser availability in the days running up to the deadline, while providing a comprehensive webchat service on the Saturday itself. This ensures we maintain full capacity during the critical weekdays when demand is highest, while still offering real-time support on the deadline day. Importantly, all remaining Self Assessment customers will be filing digitally, as the paper filing deadline passed on 31 October.
Our communications approach:
We will be clear and upfront with customers from early January, giving them time to plan ahead. From the week commencing 5 January, we will begin daily social media posts encouraging early contact and digital use, alongside clear messaging that phone lines close on Friday 30 January and reopen on Monday 2 February. On 12 January, we will include details of Saturday's webchat service in our Self Assessment payment reminder press notice, update GOV.UK contact pages, and share information through the Agent Update. From 23 January, IVR messaging will be updated to confirm no phone lines on Saturday, and on 30 January we will issue a final reminder that it is the last day for phone support.
This approach gives customers who prefer phone contact time to reach us during the week before the deadline, when we have maximum staffing in place.”
Ahead of the filing deadline, the Institute has also been made aware that delays are being experienced in client authorisations being processed and the client appearing on the agent’s client list. We have been advised that HMRC is aware of the issue and a fix has been deployed for new authorisations. All older authorisations should now be appearing on client lists.
Any further issues experienced should be reported to HMRC’s online services helpdesk in the first instance with recourse to the Institute by email if these continue to hamper efforts to file by the deadline.
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