Self Assessment liabilities are normally due, subject to Payments on Account made, on 31 January after the tax year, and if paid 30 days late carry a 5% surcharge.

For example, for 2019-20, Self Assessment Tax and NI was due 31 January 2021 and the 5% surcharge applies if unpaid by 3 March 2021.

HMRC have announced 19 February 2021 that the 5% otherwise imposed on 3 March 2021 will be waived if either (a) the liability is settled in full by 1 April 2021, or a payment plan is set up by that date.

Here is what HMRC said:

More help for Self Assessment taxpayers

Self Assessment taxpayers will not be charged a 5% late payment penalty if they pay their tax or set up a payment plan by 1 April 2021, HM Revenue and Customs (HMRC) has announced.

The payment deadline for Self Assessment is 31 January and interest is charged from 1 February on any amounts outstanding. Normally, a 5% late payment penalty is also charged on any unpaid tax that is still outstanding on 3 March. But this year, because of the impact of the COVID-19 pandemic, HMRC is giving taxpayers more time to pay or set up a payment plan.

Taxpayers can pay their tax bill or set up a monthly payment plan online at GOV.UK. They need to do this by midnight on 1 April to prevent being charged a late payment penalty.

Source – Press Release More help for Self Assessment taxpayers