Self Assessment Tax Return UK 2026: Deadlines, How to File & Penalties
CT
Chandraketu Tripathi
Finance Editor, Kaeltripton
Published4 Apr 2026
Last reviewed18 Apr 2026
✓ Fact-checked
Illustrative image. AI-generated and does not depict real people, places or events.
Advertisement
Over 12 million people in the UK must file a self assessment tax return each year. With Making Tax Digital launching in 2026 and new deadlines to navigate, here's everything you need to know. 2025/26 Tax Year
Self Assessment Key Deadlines — 2025/26 Tax Year
Deadline
Date
What You Must Do
Register for self assessment
5 October 2026
If new to self assessment for 2025/26
Paper return deadline
31 October 2026
File paper self assessment return
Online return deadline
31 January 2027
File self assessment return online
Payment deadline
31 January 2027
Pay balancing payment + 1st payment on account
2nd payment on account
31 July 2027
Pay second payment on account for 2026/27
Amend 2025/26 return
31 January 2028
Deadline to amend a filed 2025/26 return
Who Must File a Self Assessment Return?
Reason
Threshold
Notes
Self-employed
Profits over £1,000
Include all trading income
Rental income
Over £2,500 profit after expenses
Register even below this if total rent over £10,000
Income over £100,000
Total income over £100,000
For personal allowance taper/60% trap
High Income Child Benefit
Either partner earns over £60,000
HICBC — must register and pay back benefit
Company director
Most directors
Check with HMRC — some exceptions apply
Capital gains
Any taxable gains
Plus 60-day property reporting for residential property
Untaxed income
Over £2,500
Savings, investment income, foreign income etc.
Partnership
All partners
Include partnership income on personal return
How to File Your Self Assessment Return
Step 1 — Register: If new, register at gov.uk by 5 October 2026 for the 2025/26 year. Allow up to 10 working days for your UTR to arrive. Step 2 — Gather records: P60/P45 from employers; self-employment income and expenses; bank statements for interest; dividend statements; pension contribution records; rental income and expenses; investment gains/losses. Step 3 — File online: Log in at gov.uk/log-in-file-self-assessment-tax-return. Complete all relevant sections. The system calculates your tax liability automatically. Step 4 — Pay by 31 January 2027: Pay your balancing payment plus the first payment on account for 2026/27 (usually 50% of your 2025/26 liability).
Penalties for Late Filing and Late Payment
Penalty
Trigger
Amount
Immediate late filing
1 day after 31 January 2027
£100 fixed penalty
Daily penalty
3 months+ late
£10/day for up to 90 days (max £900)
6-month penalty
6 months+ late
5% of tax due or £300 (whichever greater)
12-month penalty
12 months+ late
Additional 5% or £300
Late payment interest
Any tax unpaid after 31 January
7.75% (HMRC rate from April 2026)
Late payment surcharge
30 days+ after 31 January
5% of unpaid tax
6-month surcharge
6 months+ after 31 January
Additional 5% of unpaid tax
Making Tax Digital and Self Assessment
From April 2026, self-employed people and landlords with income above £50,000 must use Making Tax Digital for Income Tax. This means quarterly digital submissions to HMRC in addition to the annual self assessment final declaration. The January 31 deadline remains for the final declaration. Quarterly submission penalties are waived for 2026/27 (grace period) but will apply from April 2027.
KAELTRIPTON VERDICT
Self assessment has never been more complex — Making Tax Digital, the High Income Child Benefit Charge, and new CGT reporting rules add to the burden. The single most important action: file on time. The automatic £100 penalty applies even if you owe no tax. Register by 5 October 2026, file by 31 January 2027, and pay by the same date. Use HMRC-recognised software to avoid errors.
Deadline 31 January 2027
Q: Who must file self assessment 2026?
A: Self-employed (profits over £1,000), landlords (rental profit over £2,500), income over £100,000, company directors, those with CGT or untaxed income over £2,500.
Q: What is the self assessment deadline for 2026?
A: Online return and payment: 31 January 2027 for 2025/26 tax year. Paper return: 31 October 2026.
Q: What are the penalties for late filing?
A: Automatic £100 from day 1. £10/day after 3 months (max £900). Further 5% or £300 after 6 and 12 months. Plus interest at 7.75% on unpaid tax.
Q: How do I register for self assessment?
A: At gov.uk/log-in-file-self-assessment-tax-return. Register by 5 October 2026 for 2025/26. Allow 10 working days for UTR to arrive.
This article is for informational purposes only and does not constitute financial or tax advice. Always consult a qualified accountant or tax adviser for your personal circumstances. All rates and figures verified from GOV.UK and official sources, April 2026.
The content on Kaeltripton.com is for informational and educational purposes only and does not constitute financial, investment, tax, legal or regulatory advice. Kaeltripton.com is not authorised or regulated by the Financial Conduct Authority (FCA) and is not a financial adviser, mortgage broker, insurance intermediary or investment firm. Nothing on this site should be construed as a personal recommendation. Rates, figures and product details are indicative only, subject to change without notice, and should always be verified directly with the relevant provider, HMRC, the FCA register, the Bank of England, Ofgem or other appropriate authority before any financial decision is made. Past performance is not a reliable indicator of future results. If you require regulated financial advice, please consult a qualified adviser authorised by the FCA.
CT
Chandraketu Tripathi
Finance Editor · Kaeltripton.com
Chandraketu (CK) Tripathi, founder and lead editor of Kael Tripton. 22 years in finance and marketing across 23 markets. Writes on UK personal finance, tax, mortgages, insurance, energy, and investing. Sources: HMRC, FCA, Ofgem, BoE, ONS.
