Self Assessment is the system HMRC uses to collect Income Tax on income not taxed at source. The deadline for 2024/25 Self Assessment returns is 31 January 2026. If you are self-employed, a landlord, or have other untaxed income, you must file a Self Assessment tax return (SA100) each year.
This guide explains who needs to file, what to report, how to submit, and what happens if you miss the deadline.
What is Self Assessment?
Self Assessment is a system where you report your income to HMRC and calculate the tax you owe. While employment income is taxed automatically through PAYE (Pay As You Earn), other income sources require you to "self-assess" your tax liability.
Each tax year, Self Assessment requires you to:
- Report all income from self-employment, property, savings, investments, and other sources
- Claim allowable expenses and reliefs you're entitled to
- Calculate your tax liability (or let software calculate it)
- Pay the tax owed by the deadline
The main Self Assessment form is the SA100. Depending on your income types, you may also complete supplementary pages:
- SA103 — Self-employment income (sole traders)
- SA105 — Property income (landlords)
- SA106 — Foreign income and savings
- SA108 — Capital gains
Who Needs to File Self Assessment?
You must file a Self Assessment tax return if any of the following apply:
Must File
- Self-employed as a sole trader with gross income over £1,000
- Partner in a business partnership
- Company director (unless non-profit with no pay or benefits)
- Total income over £150,000 from any source
- Rental income over £2,500 (or any amount if claiming expenses)
- Untaxed foreign income taxable in the UK
- Capital gains above the annual exempt amount (£3,000 for 2024/25)
- Savings or investment income over £10,000
- Received a P800 from HMRC stating you owe tax
May Need to File
- Child Benefit recipient with income over £60,000 (High Income Child Benefit Charge)
- Employee expenses to claim over £2,500
- Pension contributions exceeding the annual allowance
- Untaxed tips, commission, or casual income
If HMRC sends you a notice to file, you must complete a return even if you believe you don't owe tax.
Self Assessment Deadlines 2024/25
The 2024/25 tax year runs from 6 April 2024 to 5 April 2025. Key deadlines:
| Deadline | Action Required | |----------|-----------------| | 5 October 2025 | Register for Self Assessment (if new) | | 31 October 2025 | Paper returns deadline | | 31 January 2026 | Online returns deadline | | 31 January 2026 | Pay tax owed | | 31 July 2026 | Second payment on account (if applicable) |
Why the January Deadline Matters
HMRC receives millions of returns in January. Filing early gives you:
- Time to find missing information
- Opportunity to budget for your tax bill
- Chance to correct errors before the deadline
- Reduced stress compared to last-minute filing
What to Report on Self Assessment
Income Sources
Report all income for the tax year (6 April to 5 April):
Self-Employment Income (SA103)
- All business income received
- Allowable business expenses
- Capital allowances on equipment
Property Income (SA105)
- Rental income from UK property
- Allowable property expenses
- Mortgage interest (for 20% tax credit)
Employment Income
- Income not fully taxed through PAYE
- Benefits in kind
- Expenses claims over £2,500
Savings and Investments (SA106)
- Interest above Personal Savings Allowance
- Dividend income above Dividend Allowance
- Foreign income and gains
Capital Gains (SA108)
- Profits from selling property, shares, or other assets
- After deducting the annual exempt amount
Reliefs and Deductions
Claim all reliefs you're entitled to:
- Pension contributions — personal pension payments
- Gift Aid donations — charitable donations
- Allowable expenses — business-related costs
- Capital allowances — equipment and vehicles
- Trading losses — to offset against other income
How to File Self Assessment
Option 1: HMRC Online (Government Gateway)
HMRC's free online service at gov.uk/self-assessment:
- Create or sign in to your Government Gateway account
- Navigate to Self Assessment
- Complete each section of the SA100
- Add supplementary pages as needed
- Review calculations
- Submit and pay
Pros: Free, direct to HMRC Cons: Manual data entry, basic interface, no bank integration
Option 2: Commercial Software (Recommended)
Tax software like TaxFolio automates the process:
- Connect your bank accounts via Open Banking
- AI categorises transactions as income and expenses
- Software calculates your tax liability
- Review and adjust figures
- Submit directly to HMRC via the API
- Records stored digitally for 6+ years
Pros: Faster, fewer errors, automatic calculations, bank integration Cons: Annual cost (though often recovered through better expense claims)
Option 3: Paper Return
Download forms from HMRC and post by 31 October (3 months earlier than online):
- Request or download SA100 and supplementary forms
- Complete by hand
- Post to HMRC
- HMRC calculates your tax
Pros: No computer required Cons: Early deadline, no automatic calculations, higher error rate
Payment on Account
If your Self Assessment tax bill exceeds £1,000 and less than 80% was deducted at source (through PAYE), you must make payments on account.
Payments on account are advance payments towards next year's tax bill:
| Payment | Deadline | Amount | |---------|----------|--------| | First payment on account | 31 January | 50% of previous year's bill | | Second payment on account | 31 July | 50% of previous year's bill | | Balancing payment | 31 January | Any remaining tax owed |
Example
2023/24 tax bill: £4,000 2024/25 payments:
- 31 January 2025: £2,000 (first payment on account)
- 31 July 2025: £2,000 (second payment on account)
If your actual 2024/25 bill is £5,000, you pay an additional £1,000 on 31 January 2026, plus new payments on account for 2025/26.
You can reduce payments on account if you expect to earn less.
Late Filing Penalties
HMRC charges automatic penalties for late Self Assessment returns:
| How Late | Penalty | |----------|---------| | 1 day late | £100 (even if no tax owed) | | 3 months late | £10/day for up to 90 days (max £900) | | 6 months late | Greater of £300 or 5% of tax due | | 12 months late | Additional £300 or 5% of tax due |
Maximum penalty for 12+ months late: £1,600 plus 100% of tax owed
Late Payment Penalties
Separate from filing penalties:
| How Late | Penalty | |----------|---------| | 30 days late | 5% of tax unpaid | | 6 months late | Additional 5% | | 12 months late | Additional 5% |
Interest accrues on unpaid tax from the due date at the HMRC interest rate.
How to Register for Self Assessment
If you've never filed Self Assessment, register by 5 October following the tax year you need to file for:
Self-Employed Registration
- Go to gov.uk/register-for-self-assessment
- Select "Self-employed or sole trader"
- Create a Government Gateway account (if you don't have one)
- Complete the registration
- HMRC posts your Unique Taxpayer Reference (UTR) within 10 working days
Other Registration Types
- Landlord — Register as a non-self-employed individual with rental income
- Company director — Register as a company director
- Partners — Register for partnership Self Assessment
Your UTR is a 10-digit number required to file your return.
Common Self Assessment Mistakes
1. Wrong Tax Year
Ensure income matches 6 April to 5 April. Income received on 6 April 2025 belongs to 2025/26, not 2024/25.
2. Missing Income
Report all income, even if tax was already deducted:
- Bank interest
- Dividend income
- Casual earnings
- Foreign income
3. Overclaiming Expenses
Only claim expenses "wholly and exclusively" for business. Mixed-use items (like phones) require apportionment.
4. Not Keeping Records
HMRC requires records for 6 years after the tax year. Keep:
- Invoices and receipts
- Bank statements
- Mileage logs
- Expense evidence
5. Missing the Deadline
Set reminders well before 31 January. HMRC systems become slow in the final days before the deadline.
Self Assessment and Making Tax Digital
From April 2026 (income over £50,000) or April 2027 (income over £30,000), Self Assessment changes significantly under Making Tax Digital:
| Current System | MTD System | |----------------|------------| | Annual return | Quarterly updates + final declaration | | Paper records allowed | Digital records required | | Software optional | HMRC-recognised software required | | 31 January deadline | Quarterly deadlines + 31 January |
TaxFolio is HMRC-recognised for both Self Assessment and MTD, providing a seamless transition.
File Your Self Assessment with TaxFolio
TaxFolio automates Self Assessment for UK self-employed individuals and landlords:
- Bank connection imports transactions automatically via Open Banking
- AI categorisation sorts expenses into correct tax categories
- Real-time calculations show your tax position as you go
- Direct HMRC submission files your return in one click
- 6-year record storage meets HMRC requirements
- MTD-ready for the transition to quarterly reporting
Start your free 30-day trial and file your Self Assessment in 15 minutes.