Who needs to file a Self Assessment tax return in the UK?

You must file a Self Assessment return if you are self-employed (sole trader or partner) with income above £1,000, a company director (unless your only income is PAYE with no other untaxed income), a landlord with rental income above £2,500 net (or £10,000 gross) after allowable expenses, earn more than £100,000 in total income, receive untaxed income above £2,500, have foreign income, made capital gains above the annual exempt amount, or claim Child Benefit while your household income is above £60,000 (High Income Child Benefit Charge).

What are the Self Assessment deadlines for 2025/26?

For the 2025/26 tax year (April 6, 2025 to April 5, 2026): register by October 5, 2026; file on paper by October 31, 2026; file online by January 31, 2027. Tax payment (balance due) must also be paid by January 31, 2027. The second Payment on Account for 2024/25 is due July 31, 2026. First Payment on Account for 2025/26 is due January 31, 2027 (combined with the balance payment).

What is Payment on Account in Self Assessment?

Payment on Account (POA) is an advance payment towards your next tax year's bill. It applies when your Self Assessment tax bill (excluding Capital Gains Tax) exceeds £1,000 and less than 80% was collected via PAYE. HMRC requires two advance payments: 50% of last year's bill on January 31 and 50% on July 31. If your income changes significantly, you can apply to reduce your POA — but underpaying by too much results in interest charges.

What are the penalties for filing or paying late?

Late filing: £100 fixed penalty immediately (applies even if you owe no tax or have already paid). After 3 months: £10 per day for up to 90 days (maximum £900). After 6 months: 5% of tax due or £300, whichever is greater. Late payment: 5% of unpaid tax after 30 days, 5% after 6 months, 5% after 12 months. Interest also accrues on unpaid tax from the due date.

UK Self Assessment Tax Return 2026 — Who Must File, Deadlines & How To

Self Assessment is the UK system for reporting income that is not taxed at source through PAYE. If you are self-employed, a landlord, a company director, or earn above certain thresholds, you are responsible for calculating and paying your own tax by completing a Self Assessment return. For the 2025/26 tax year, the online filing deadline is January 31, 2027, with payment of any balance also due that day. Missing the deadline triggers an immediate £100 fine — even if you owe no tax.

Quick answer: You need to file Self Assessment if you are self-employed, a landlord, earn over £100,000, or have untaxed income above £2,500. Register by October 5, 2026. File online by January 31, 2027. Pay any tax owed by January 31, 2027.

Self Assessment: Key Dates for 2025/26

Deadline	Date	What You Must Do
Register for Self Assessment	October 5, 2026	Register if filing for the first time for 2025/26
Paper return deadline	October 31, 2026	File paper SA100 form
Online return deadline	January 31, 2027	File online via HMRC or compatible software
Balance payment deadline	January 31, 2027	Pay remaining 2025/26 tax due
First 2025/26 Payment on Account	January 31, 2027	50% of estimated 2025/26 bill (combined with balance)
Second 2025/26 Payment on Account	July 31, 2027	50% of estimated 2025/26 bill

Who Must File Self Assessment?

You must register and file a Self Assessment return if any of the following apply in the 2025/26 tax year:

Situation	Threshold
Self-employed (sole trader or partner)	Gross income > £1,000
Landlord	Rental income > £10,000 gross OR > £2,500 net after expenses
Company director	Always (unless only income is PAYE with no other untaxed income)
High earner	Total income > £100,000
High Income Child Benefit Charge	Household income > £60,000 with Child Benefit claimed
Untaxed income	Untaxed income > £2,500 (e.g., tips, commission)
Capital gains	Gains above the annual exempt amount (£3,000 for 2025/26)
Foreign income	Any foreign income (except PAYE-taxed employment)
Trust or estate	As a trustee or executor

If you are unsure, HMRC provides a tool at gov.uk/check-if-you-need-to-send-a-self-assessment-tax-return.

How to Register for Self Assessment

If you have never filed Self Assessment before:

Go to gov.uk/register-for-self-assessment
Register by October 5 following the tax year you need to file for
HMRC will post your Unique Taxpayer Reference (UTR) — this takes up to 10 days
Set up your Government Gateway account to file online
Activate your online Self Assessment account using the activation code HMRC sends by post

New to self-employment: register as self-employed separately at gov.uk/register-for-self-employment.

What to Include on Your Return

Your Self Assessment return (form SA100 and any supplementary pages) must include:

Employment income — from all PAYE jobs (from P60s)
Self-employment income — profits from your business (SA103 supplementary form)
Partnership income — from your share of partnership profits (SA104)
Rental income — from UK land and property (SA105)
Foreign income — dividends, employment, pensions from abroad (SA106)
Capital gains — from property, shares, or assets sold (SA108)
Pension income — if not already taxed by the provider
Dividend income — from shares in UK/foreign companies
Interest — from bank accounts, savings, investments
Gift Aid donations — extends basic-rate band; higher-rate taxpayers claim additional relief

Keep all supporting documents (P60s, bank statements, rental accounts, receipts, invoices) for at least 5 years after the filing deadline.

Payment on Account

Payment on Account (POA) applies when your Self Assessment tax bill (excluding CGT) is:

More than £1,000, AND
Less than 80% was collected via PAYE or another deduction at source

HMRC then requires you to pay your next year’s tax in two advance instalments:

POA Instalment	Amount	Due Date
First Payment on Account	50% of previous year’s tax bill	January 31
Second Payment on Account	50% of previous year’s tax bill	July 31
Balancing payment	Actual tax minus POAs paid	January 31 (following year)

Example: Sarah’s 2024/25 Self Assessment tax bill is £8,000. She must pay:

January 31, 2026: £8,000 (balance) + £4,000 (first 2025/26 POA) = £12,000
July 31, 2026: £4,000 (second 2025/26 POA)
January 31, 2027: actual 2025/26 bill minus the £8,000 already paid in POAs

Reducing POA: If your income will be lower next year, apply to reduce POA at gov.uk — but be careful, as underpaying triggers interest charges.

How to File Online

Sign in to your HMRC online account at gov.uk/personal-tax-account
Navigate to Self Assessment → File a return
Complete each section for your income types
HMRC’s tool calculates your tax bill automatically
Check the calculation carefully before submitting
Pay online via bank transfer, debit card, or Direct Debit

Compatible software: HMRC accepts returns via commercial software (QuickBooks, Xero, Sage, FreeAgent). Making Tax Digital (MTD) for Income Tax is being phased in — self-employed individuals and landlords with income above £50,000 must use MTD-compatible software from April 2026.

Penalties for Late Filing and Payment

Missing the January 31 deadline immediately triggers a £100 penalty — even if you owe no tax or have already paid.

Delay	Penalty
Filed/paid late	£100 immediately
3 months late	£10/day × 90 days = up to £900
6 months late	5% of tax due or £300 (whichever is greater)
12 months late	Further 5% penalty
Late payment (30 days)	5% of unpaid tax
Late payment (6 months)	Additional 5%
Late payment (12 months)	Additional 5%
Interest	Accrues daily from January 31 on unpaid balance

File even if you cannot pay — the late filing penalty is separate from late payment interest. Filing on time avoids the filing penalty, and you can arrange a Time to Pay arrangement with HMRC for any tax you cannot pay immediately.

Self Assessment Calculator — estimate your Self Assessment bill
National Insurance Guide — Class 2 and 4 NI for self-employed
Capital Allowances Guide — deduct business equipment costs
Employment Allowance 2026 — reduce employer NIC bill
UK Taxes Hub — all UK tax guides for 2026

Filing Self Assessment is mandatory if you have untaxed income — the consequences of not filing include escalating penalties and HMRC investigations. Register early (by October 5), gather your records, and file online well before January 31 to avoid the last-minute rush and potential filing issues.

Written by WealthVieu

WealthVieu researches and writes data-driven personal finance guides using primary sources including the IRS, Bureau of Labor Statistics, Federal Reserve, and Census Bureau.

The content on Wealthvieu is for informational purposes only and should not be considered financial, tax, or investment advice. Consult a qualified professional before making financial decisions. Full disclaimer · Editorial policy