What do I need to do my tax return online?

Below is a handy checklist of what you need to gather together in order to fill out your return, as well as a reminder of the penalties you face for missing the deadline. What more incentive do you need?

Tax return checklist

To register:

  • Unique taxpayer reference (10-digit tax reference found on HM Revenue & Customs paperwork)
  • National insurance number or postcode
  • Activation code. This will be posted to you and must be input afterwards to complete registration. 

To fill in the self-assessment:

  • User ID. You will receive this after registering
  • Note of online password
  • Copies or a record of all invoices of self-employed work 
  • Receipts of any expenses you want to offset (such as transport or office costs)
  • Pension contributions
  • Details of any charity gifts
  • Note of any other sources of income (savings accounts and buy-to-let property)
  • Interest certificates from savings accounts (not including tax-free products such as ISAs)
  • P60. This applies to those in employment who do additional self-employed work


  • £100 if you’re one day late (up to three months)
  • After three months you’re charged £10 for each day late (capped at £900).
  • After six months you will have to pay 5% extra on tax owed, or £300, whichever is greater

More about