Self Assessment Deadlines UK 2025: What You Need to Know and How to Avoid Penalties
Missing the Self Assessment deadline costs you money. Find out the key dates for the 2024–25 tax year, what happens if you file late, and how to get your return done on time.
1/3/20261 min read
Every year, thousands of self-employed workers and CIS subcontractors in the UK miss the Self Assessment deadline — and pay the price. An automatic £100 fine, further daily penalties, and unnecessary stress.
It does not have to be that way. Here are the key dates you need to know and what to do to stay on the right side of HMRC.
Key Self Assessment dates for the 2024–25 tax year
6 April 2025 — The new tax year begins.
5 October 2025 — Deadline to register for Self Assessment if you are filing for the first time.
31 October 2025 — Deadline for paper tax returns.
31 January 2026 — Deadline for online tax returns and any tax owed.
The most important date is 31 January 2026. This is the deadline for filing your 2024–25 tax return online and paying any tax you owe.
What happens if you miss the deadline?
Day 1 late: automatic £100 penalty — even if you have no tax to pay.
3 months late: £10 per day for up to 90 days (up to £900).
6 months late: an additional 5% of the tax owed or £300, whichever is higher.
12 months late: a further penalty on top.
Missing the deadline is never worth it. Even if you cannot pay the tax straight away, filing on time avoids the automatic penalties.
What if you have missed a previous year?
You can still file late returns going back up to 4 years. The sooner you file, the sooner any penalties stop growing — and the sooner you can claim any refund you are owed.
Who needs to file a Self Assessment return?
You need to file if you are:
— Self-employed as a sole trader
— A CIS subcontractor
— A landlord with rental income
— Someone with untaxed income above £1,000
If you are not sure whether you need to file, contact us and we will advise you for free.
How TD Tax Return can help
We prepare and submit your Self Assessment return accurately and on time — with fixed fees from £180, no hidden costs, and no surprises.
The process is fully online. You do not need to visit an office or attend meetings. We handle everything and keep you informed at every step.
Get in touch today
Email info@tdtaxreturn.com or book a free consultation at tdtaxreturn.com.
Services available in English, Hungarian, and Romanian.
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