Get Ahead of Self Assessment: Why September Is the Best Time to Start Preparing

Why start in September?

There are several practical reasons why getting ahead now pays dividends later.
First, your 2025/26 tax year ended on 5 April 2026 (which means all of the information you need for your return already exists. Income records, expenses, investment income, rental receipts) it is all there. The sooner you gather it, the less likely you are to overlook something important.

Second, September tends to be a slightly quieter month for many businesses. Carving out a few hours now (rather than during the busy autumn or Christmas period) is simply easier.
Third, if you engage an accountant to prepare your return, early submission means your accountant can give your return proper attention rather than working under deadline pressure alongside dozens of other clients.

What information will you need?

The exact documents you need will depend on your personal circumstances, but most Self Assessment returns draw on some or all of the following:

• Employment income — P60 from your employer, or P45 if you left a job during the year
• Self-employment income — sales records, invoices, and bank statements for the 2025/26 tax year
• Rental income — records of rent received and allowable expenses for any let properties
• Investment income — dividend vouchers, interest statements from savings accounts
• Capital gains — details of any assets sold during the year, including property and shares
• Pension contributions — records of any personal pension contributions made
• Gift Aid donations — receipts for any charitable donations made under Gift Aid

If you are unsure what applies to you, your accountant can provide a tailored checklist based on your specific circumstances.