The deadline for filing self-assessment tax returns online for 2017/18 and for paying any remaining tax for 2017/18 is 31 January 2019.
The deadline also applies for the self-employed to pay their Class 2 and the balance of any Class 4 National Insurance contributions due for 2017/18.
The first payment on account of the 2018/19 liability is also due by 31 January 2019.
Penalties are charged where returns are filed late and tax paid late. Interest is also charged on late payments.
Comment: HMRC produce a tool which can be used by an individual to check whether they need to submit a self-assessment tax return. The tool is available on the Gov.uk website at