Tax & HMRC
⏱ 5 min read
📅 Updated Apr 2026
Self Assessment Tax Return UK 2026: Deadlines, How to File & Penalties
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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 |
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| 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 |
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| 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 ReturnStep 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 |
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| 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 AssessmentFrom 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. |
Part of our complete guide: UK Income Tax Rates 2026-27 - Complete Guide → Find a regulated IFA for tax planning →
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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.
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