Self Assessment Checklist: Everything You Need Before You Start

2nd January 2026

Before you dive into completing your Self Assessment tax return, it's crucial to gather all the necessary documents and information first. Nothing is more frustrating than getting halfway through your return only to realise you're missing key paperwork. Here's your comprehensive checklist to ensure you have everything you need.

Personal Information

You'll need:

• Your National Insurance number
• Your Unique Taxpayer Reference (UTR) number (this is a 10-digit number HMRC will have sent you)
• Your Government Gateway user ID and password for online filing
• Details of any previous tax returns you've submitted

If you haven't registered for Self Assessment before, you'll need to do this immediately. HMRC can take up to 10 working days to send you an activation code, so don't delay.

Employment Income

If you've been employed during the tax year (6th April 2024 to 5th April 2025), gather:

• Your P60 (End of Year Certificate) showing your total pay and tax deducted
• Any P45s if you've changed jobs or been made redundant
• P11D forms showing any benefits in kind (company car, private medical insurance, etc.)
• Payslips if you don't have a P60 yet
• Details of any tips, bonuses, or commission not shown on your P60

Self-Employment Income

Self-employed individuals and partnerships need:

• Complete records of all business income received
• Bank statements showing business transactions
• Invoices issued and received
• Records of all business expenses (more on this in a future blog)
• Details of any goods or services you've taken from the business for personal use
• Details of any capital allowances (equipment, vehicles, etc.)
• Records of any Construction Industry Scheme (CIS) deductions

Property Income

Landlords must provide:

• Total rental income received from all properties
• Details of all allowable expenses (repairs, insurance, letting agent fees, etc.)
• Mortgage interest paid (note: tax relief has changed in recent years)
• Details of any property disposal or acquisition
• Wear and tear allowance information (for furnished lettings)

Investment and Savings Income

Gather information about:

• Bank and building society interest (most banks provide an annual certificate)
• Dividend income from shares (check your dividend vouchers and annual statements)
• Income from trusts, settlements, or estates
• Foreign dividends and interest
• Peer-to-peer lending income

Other Income Sources

Don't forget about:

• State benefits (if taxable)
• Income from overseas sources
• Pension income (including State Pension)
• Trust income
• Any other untaxed income

Capital Gains and Losses

If you've sold or disposed of assets, you'll need:

• Details of assets sold (property, shares, business assets, etc.)
• Purchase prices and dates
• Sale prices and dates
• Associated costs (legal fees, estate agent fees, improvement costs)
• Details of any losses from previous years you're carrying forward

Reliefs and Allowances

Gather records of:

• Pension contributions (personal and employer contributions)
• Gift Aid donations to charity
• Maintenance payments (if applicable)
• Venture Capital Trust or Enterprise Investment Scheme investments
• Professional subscriptions and fees
• Work from home expenses

Payment Records

If you've already made payments on account or other tax payments during the year, have these details to hand:

• Dates and amounts of any payments made
• Payment reference numbers
• Details of any refunds received

Top Tips for Organisation

1. Create a folder system: Whether digital or physical, keep everything in one place
2. Use your bank statements: These can help identify income and expenses you might have forgotten
3. Check your emails: Many statements and certificates are now sent electronically
4. Contact providers early: If you're missing documents, request copies now rather than in late January
5. Keep records: You must keep your tax records for at least five years after the 31st January submission deadline

Still Missing Something?

If you're missing crucial documents, here's what to do:

• P60/P45: Contact your employer's payroll department
• Bank interest certificates: Log into your online banking or call your bank
• Dividend vouchers: Contact the company's share registrar
• Previous tax returns: You can view these through your HMRC online account

Ready to Start?

Once you've gathered all this information, you're ready to begin completing your tax return. If you're looking at this list and feeling overwhelmed, remember that professional help is available. At MCC Partners, we can handle the entire process for you, ensuring nothing is missed and your return is optimised for your circumstances.

Tomorrow, we'll be covering guidance specifically for first-time filers who might be feeling particularly daunted by the process.

Need help getting organised? Contact MCC Partners on 01474 619 990 or email This email address is being protected from spambots. You need JavaScript enabled to view it.. We're here to make Self Assessment straightforward.