What Do You Need for Self Assessment? [Full Checklist]

Self Assessment doesn’t have to be stressful, confusing, or last-minute. The key to filing accurately and on time is preparation. When you know exactly what information and documents you need before you start, the entire process becomes more efficient and less error-prone.

So, what do you need for Self Assessment? This guide breaks down what freelancers, sole traders, landlords, and other taxpayers need when completing a UK Self Assessment tax return, so you can stay compliant and avoid unnecessary penalties.

Key points

• Gather every source of taxable income 📋
  Every type of income you receive throughout the year needs to be reported. Keeping complete records helps you avoid missing income that could affect your tax bill.
• Keep detailed expense and asset records 💷
  Keep receipts, dates, amounts, and business-use details, and separate personal and business costs where necessary.
• Check tax reliefs, loans, and previous payments 🔎
  Pension contributions, Gift Aid, and certain investments can affect your tax position. You may also need student loan and Child Benefit information, previous losses and details of payments already made to HMRC.
• Keep your records organised throughout the year with ANNA 🚀
  Instead of gathering a year's worth of information at the last minute, ANNA can automatically track income and spending, scan and categorise receipts, keep your tax position up to date, and calculate and file Self Assessment.

What is Self Assessment, and why does it matter?

Self Assessment is HMRC’s way of collecting tax from people whose income isn’t fully taxed at source. Instead of tax being deducted automatically, you’re responsible for reporting your income, calculating what you owe, and paying it on time.

You’ll usually need to file a Self Assessment tax return if you:

• Are self-employed or freelance
• Run a small business or side hustle earning over £1,000
• Earn rental income from property
• Are a company director with additional untaxed income
• Receive income from dividends, investments, or savings
• Made money from selling assets such as crypto, property, or stocks and shares
• Have foreign income
• Have to pay the High Income Child Benefit Charge and don’t pay it through PAYE

Even if your income feels straightforward, HMRC still expects accurate records and timely submissions. Missing information or filing late can trigger penalties that can quickly add up if you aren’t cautious.

The Self Assessment timeline

Understanding the deadlines is just as important as knowing what documents you need. Most Self Assessment problems happen because people start their preparation too late.

Here are the key dates to keep in mind:

• 5 October (after the end of the tax year) – Deadline to register for Self Assessment with HMRC
• 31 October – Deadline for submitting a paper Self Assessment tax return (if you choose to do so via post instead of online)
• 31 January – Deadline for submitting your online Self Assessment tax return and paying any tax owed via Self Assessment (if you choose to do so online instead of via post)
• 31 July – Deadline for making the second payment on account; applies only if your last Self Assessment bill was over £1,000, and less than 80% of your tax was collected at source

The tax year runs from 6 April to 5 April. Still, waiting until January to organise everything is more likely to make you stressed, which can increase the risk of mistakes.

What do you need for Self Assessment?Your practical Self Assessment checklist

This checklist covers what most individuals and small businesses need to complete a UK Self Assessment tax return. Not every section will apply to everyone, but missing even one relevant item can lead to penalties or tax issues.

Here are eight things you need to have for your Self Assessment:

1. Your personal and HMRC details

Before anything else, make sure you have your core personal and tax identifiers ready. These details are required to access HMRC services and submit your return:

• Unique Taxpayer Reference (UTR) – A 10-digit number issued by HMRC when you register for Self Assessment
• National Insurance number – A personal identifier used by HMRC to track your tax, National Insurance contributions, and state benefits
• Government Gateway user ID and password – Your login details for accessing HMRC’s online services and submitting your tax return
• Registered address (as held by HMRC) – The address HMRC has on file for you, used for correspondence and identity checks
• Date of birth – Used by HMRC to verify your identity when accessing or managing your tax account

Make sure the address HMRC has on file is up to date. Mismatched details can cause login issues or delays if HMRC needs to contact you.

If you’ve lost your UTR or Government Gateway details, recovery can take days or weeks, especially during peak filing season.

2. Your income records

HMRC expects you to report all taxable income for the tax year, even if it comes from multiple sources. Below are the main income types to review carefully.

Self-employment income

If you’re a sole trader or freelancer, you’ll need records showing exactly how much your business earned during the tax year, including:

• Invoices issued during the tax year – Records showing what you charged customers during the tax year, including dates and amounts
• Records of payments received – Evidence of money paid to you, such as bank statements or payment confirmations
• Cash income – Any business income received in cash that may not appear in bank records
• Tips, commissions, and bonuses – Additional earnings linked to your work that are still taxable income
• Any income earned abroad (converted to GBP) – Income earned outside the UK, converted to pounds using HMRC-approved exchange rates

Your income should be recorded on an accruals basis (when invoiced) or a cash basis (when paid), depending on which accounting method you use. The cash basis is the standard method to record income, but you may elect to use the accruals (‘traditional’) method if you wish.

Employment income (PAYE)

If you have a job but also run your own business, you still need to declare your PAYE earnings.

You’ll need to gather:

• Form P60 – A summary of your total pay and tax deducted by an employer during the tax year
• Form P45 – A statement showing pay and tax deducted when you leave a job partway through the year
• Form P11D – A record of non-cash benefits provided by your employer, such as a company car or private medical cover

Even though tax is deducted automatically, this contributes to your total taxable income and affects thresholds for student loan repayments, tax allowances (Personal Allowance, Marriage Allowance, Personal Savings Allowance, etc.), and Child Benefit charges.

Property income

If you earn income from renting property, it must be reported separately from self-employment income.

You’ll need:

• Total rental income received – The full amount of rent paid to you during the tax year, before expenses
• Rent from furnished or unfurnished property – Rental income from standard residential property, regardless of furnishing status
• Holiday let income – Income from short-term or holiday rentals in the UK or overseas
• Advance rent payments – Rent paid in advance that must be declared in the year it’s received
• Rental arrears received – Late rent payments collected during the tax year, even if they relate to earlier periods

Keep in mind that rental income is taxed based on when it’s received, not when it’s due (unless you elect to be taxed under the accruals/traditional basis). This is important because it determines which tax year the income applies to, affects how much tax you owe, and ensures your Self Assessment is accurate.

Sale of capital assets

If you sell assets and make a profit of more than £3,000, you need to declare these to HMRC in the tax year in which you made the sale. Check whether you sold:

• Cryptocurrency
• Cars, watches, jewellery, antiques - If trading in these assets
• Property - You may get tax relief if you sell your main residence
• Assets based overseas 
• Stocks and shares - Unless held in ISAs or PEPs

You may still need to report a sale of assets even if you make a profit of less than £3,000; for example, if you sell them at a price of more than £50,000. Also, you may need to report a sale if you gift assets away.

Other income sources

Many people miss income that feels ‘minor’ or irregular, but HMRC still expects it to be declared. Check whether you received:

• Savings interest – Interest earned on bank or building society accounts
• Dividends – Income received from shares or investment funds
• Pension income – Payments received from private or workplace pensions
• Trust or settlement income – Income paid to you from a trust or settlement arrangement
• Casual or side-hustle income – Irregular or secondary income not covered by employment or main self-employment
• Foreign income - Income you receive from overseas sources, such as rental property, bank accounts, or investments 

Even small amounts can affect your tax position, especially if they push you into a higher tax band.

3. Your business expenses

Claiming allowable expenses reduces your taxable profit, but only if you have accurate records to support them.

Common allowable expenses include:

• Office supplies and stationery
• Software subscriptions and digital tools
• Phone and internet (business proportion)
• Marketing and advertising
• Professional fees (accountants, legal advice)
• Insurance (business-related)
• Bank charges and interest
• Training courses (related to existing skills)

If you own rental property, common allowable expenses include:

• Mortgage interest
• Service and management charges
• Repairs and maintenance
• Professional fees (accountants, solicitor fees, legal advice)
• Insurance 

To claim them, these expenses need to be:

• Wholly and exclusively for business purposes
• Supported by a receipt or record
• Recorded with the correct date and amount

Mixed-use expenses (such as phone bills or home broadband) must be apportioned fairly between business and personal use.

Travel and vehicle costs

If you travel for work, you may be able to claim related costs. Depending on your method, you’ll need:

• Mileage records (date, distance, purpose)
• Fuel receipts
• Vehicle repairs and servicing
• Insurance and road tax
• Parking fees (not fines)

You can usually claim either mileage allowance or actual vehicle costs, not both.

Home office expenses

If you work from home, you may be able to claim a portion of household costs, such as:

• A proportion of rent or mortgage interest
• Electricity and gas
• Council tax
• Internet costs

Claims must reflect actual business use. Alternatively, HMRC offers a simplified flat-rate method based on hours worked from home, which can reduce record-keeping but may not always give the highest deduction.

4. Capital allowances and asset purchases

Some purchases can’t be claimed as regular expenses, but may qualify for capital allowances, allowing you to deduct their cost over time.

These are the assets to track:

• Laptops and computers
• Office furniture
• Machinery or equipment
• Tools used for work
• Vehicles used for business

For each asset, record:

• Purchase date
• Purchase cost
• Business-use percentage

Many assets qualify for the Annual Investment Allowance (AIA), which allows a full deduction in the year of purchase, but the rules vary by asset type.

5. Pension contributions and tax reliefs

Pension contributions can significantly reduce your tax bill, but only if they’re reported correctly.

Gather details of:

• Total personal pension contributions – Payments you made into a private pension during the tax year
• Employer pension contributions – Contributions made by an employer on your behalf
• Relief-at-source contributions – Pension payments where basic-rate tax relief is added automatically
• Contributions to overseas pensions (if applicable) – Contributions to qualifying pensions outside the UK

You may also need information on:

• Gift Aid donations – Charitable donations that qualify for tax relief
• Enterprise Investment Scheme (EIS) investments – Investments in qualifying companies that may offer income tax relief
• Seed Enterprise Investment Scheme (SEIS) – Early-stage investments that provide enhanced tax relief
• Venture Capital Trust (VCT) investments – Investments in Venture Capital Trusts that can reduce income tax

These reliefs can extend your basic rate band and reduce higher-rate or additional-rate tax, making accurate reporting especially important.

6. Student loan and Child Benefit information

Some sections of Self Assessment only apply in specific situations but can significantly affect your final bill.

Student loan repayments

If you’re liable for student loan repayments, you’ll need:

• Your loan plan type (Plan 1, Plan 2, Plan 4, or Postgraduate)
• Confirmation that repayments apply for the tax year

HMRC uses your total income to calculate repayments, including income not taxed through PAYE.

Child Benefit charge

If you or your partner received Child Benefit, and your income exceeds the threshold, gather:

• Total Child Benefit received
• Dates payments were received
• Partner’s income (if relevant)

This determines whether the High Income Child Benefit Charge applies, and how much needs to be repaid.

7. Previous losses and adjustments

If you’ve made losses in previous years, you may be able to offset them against current profits.

You’ll need to prepare records showing:

• Losses carried forward – Business losses from earlier years used to reduce current or future profits
• Losses carried back – Losses applied to earlier tax years to reclaim tax that is already paid
• Earlier return adjustments – Changes made to previous tax returns that affect current figures
• HMRC correspondence – Letters or notices from HMRC relating to amendments or enquiries

8. Payments already made to HMRC

Before submitting your return, check what you’ve already paid to avoid confusion or overpayment.

Review your:

• Payments on account – Advance payments towards your next tax bill based on previous liabilities
• Balancing payments – Extra payments made to settle your final tax bill for the year
• Tax refunds received – Money repaid by HMRC that may affect your overall position

Having this information helps you understand your final bill and cash-flow position.

Final checks before submission

Before submitting your return, run through this final checklist:

HMRC can open enquiries up to several years after the submission deadline, so keep your records for at least five years after the submission deadline. 

For companies, accounting and tax records should be kept for at least six years. In cases of fraud, HMRC can go back even further.

Stay on top of Self Assessment with ANNA

Self Assessment doesn’t have to be something you dread every January. Most of the stress comes from trying to organise a year’s worth of income, expenses, and receipts all at once.

However, when your finances are already structured and up to date, filing your tax return becomes a straightforward admin task rather than a last-minute scramble. That’s where ANNA steps in.

ANNA can:

• Automatically calculate and file your Self Assessment with MTD-ready smart automation
• Keep your finances organised all year with automatic income and spending tracking
• Make expenses and receipts easy to manage with receipt scanning and automatic expense categorising
• Give you visibility into what you might owe with up-to-date automated summaries of your income, expenses, and tax position
• Reduce admin and last-minute stress with everything already organised in one place, making the process faster, simpler, and far less stressful

If you want to spend next to no time on admin, and more time running your business, open an ANNA account and simplify your Self Assessment.