Self Assessment Tax Return in London

Who needs to complete a self assessment tax return

What are the main things I need to know about self assesment

Tax year

A tax year runs from 6 April to 5 April. A tax return must be filed electronically by 31 January the following year or by 31 October if you are filing using a paper tax return.

Payment dates

Tax must be paid by 31 January following the 5 April tax year. If you fall under the "payment on account" rules, you must also make a payment in respect of the following year on 31 January and 31 July.

What if I do nothing

Tax penalties

If you have a reasonable excuse, HMRC will remove the penalties. What you think is reasonable might be at odds with HMRC and often these disputes are taken to a tax tribunal for an independant decision. If HMRC disagree with your excuse, the following HMRC tax penalties await you:

  • 1 day late - £100
  • 3 months late - £10 per day, a max of £900
  • 6 months late - £300
  • 12 months late - £300


If you will struggle to pay you tax bill - HMRC may agree a time to pay arrangement with you depending on your personal circumstances. If you don't speak to HMRC and don't pay your tax the following interest charges appy:

  • 5% - if the payment is 30 days late
  • A further 5% - if the payment is 6 months late
  • A further 5% - if the payment is 12 months late

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