UK Self Assessment Tax Return: Complete Filing Guide 2024/25

What Is Self Assessment?

Self Assessment is the system HMRC uses to collect Income Tax from individuals whose tax is not fully collected through PAYE (Pay As You Earn). If you have income that is not taxed at source, or if your tax affairs are complex, you may need to file a Self Assessment tax return.

Who Needs to File?

You must register for Self Assessment and file a return if you:

Are self-employed as a sole trader earning more than 1,000 GBP

Are a partner in a business partnership

Earned more than 150,000 GBP in the tax year

Had income from property rentals

Received income from abroad

Received dividends above the dividend allowance

Owe Capital Gains Tax on disposals

Are a company director (some exceptions)

Received child benefit and you or your partner earned above 60,000 GBP

Owe tax that was not collected through PAYE

Key Dates for 2024/25 Tax Year

5 October 2025: Register for Self Assessment if filing for the first time

31 October 2025: Paper return deadline

31 January 2026: Online return deadline and payment due for balancing payment

31 January 2026: First payment on account for 2025/26

31 July 2026: Second payment on account for 2025/26

What Are Payments on Account?

If your tax bill exceeds 1,000 GBP and less than 80% was collected at source, HMRC requires advance payments toward next year's bill. Each payment is 50% of the previous year's tax liability.

Getting Started

Register for Self Assessment

Go to gov.uk and register for Self Assessment

You will receive a Unique Taxpayer Reference (UTR) by post within 10 working days

Create a Government Gateway account if you do not have one

Activate your Self Assessment online service

Your UTR Number

Your 10-digit UTR is essential. Keep it safe. You will need it every year.

Income Tax Rates 2024/25

England, Wales, and Northern Ireland

Band	Taxable Income	Rate
Personal Allowance	Up to 12,570 GBP	0%
Basic Rate	12,571 - 50,270 GBP	20%
Higher Rate	50,271 - 125,140 GBP	40%
Additional Rate	Over 125,140 GBP	45%

Scotland (different rates)

Scotland has its own income tax bands with starter (19%), basic (20%), intermediate (21%), higher (42%), advanced (45%), and top (48%) rates.

Personal Allowance Taper

Your Personal Allowance reduces by 1 GBP for every 2 GBP of income above 100,000 GBP. At 125,140 GBP, the Personal Allowance is zero.

National Insurance Contributions

Class 2 NIC (Self-Employed)

3.45 GBP per week if profits exceed 12,570 GBP

Voluntary for those below threshold to maintain state pension qualifying years

Class 4 NIC (Self-Employed)

6% on profits between 12,570 and 50,270 GBP

2% on profits above 50,270 GBP

Allowable Business Expenses

If self-employed, you can deduct legitimate business expenses:

Office costs (stationery, phone, internet)

Travel costs (fuel, parking, public transport for business)

Clothing expenses (uniforms, protective clothing)

Staff costs (salaries, subcontractors)

Stock and materials

Financial costs (insurance, bank charges)

Business premises costs (rent, rates, utilities)

Advertising and marketing

Training courses related to your business

Professional subscriptions and memberships

Simplified Expenses

HMRC offers flat rates for:

Vehicles: 45p per mile (first 10,000 miles), 25p thereafter

Working from home: 6 GBP per week (or actual costs if higher)

Living at business premises: 350-650 GBP per month depending on occupants

Completing Your Return

The main sections of the Self Assessment return include:

Personal details and tax year

Employment income (SA102)

Self-employment income (SA103S for short, SA103F for full)

Partnership income (SA104)

UK property income (SA105)

Foreign income (SA106)

Capital gains (SA108)

Additional information (SA101)

Tax-Efficient Strategies

Use your full Personal Allowance and your spouse's if applicable through Marriage Allowance

Maximize pension contributions for tax relief at your marginal rate

Use ISA allowances - 20,000 GBP per year tax-free

Claim Marriage Allowance if one partner earns below 12,570 GBP (saves up to 252 GBP)

Utilize the trading allowance - first 1,000 GBP of trading income is tax-free

Carry forward losses from previous years to offset current profits

Filing with Taxation.ai

Taxation.ai supports UK Self Assessment filing with AI-powered expense categorization, automatic calculation of Class 2 and Class 4 NIC, and multi-country support for those with international income. Upload your records and let AI handle the complexity.