As existing Self-Assessment tax filers will be aware, the deadline for online submission of your 2016-17 Self-Assessment tax return is 31 January 2018. This is also the date that the payment is due for the balance of any Self-Assessment liability for 2016-17, and the due date for any payment on account due for the current 2017-18 tax year.There are penalties for late Self-Assessment returns including an automatic £100 penalty for submitting a late return even if there was no tax to pay or the tax due was paid on time.The following additional penalties apply to Self-Assessment returns that are filed late:From 3 months late: taxpayers will be charged an automatic daily penalty of £10 per day up to a £900 maximum.From 6 months late: taxpayers will be charged additional penalties which are the greater of 5% of tax due or £300.Over 12 months late: there are additional penalties based on greater of 5% of tax due or £300. In serious cases this penalty may be increased up to 100% of tax due.If you are struggling to meet the 31 January 2018 filing deadline we can help.Planning noteThe filing deadline for taxpayers with certain underpayments in the 2016-17 tax year, and who want to apply to have tax collected through their tax code (in 2018-19), is even earlier – 30 December 2017.Completing your 2017 tax return will also ensure that you know how much you will need to pay HMRC at the end of January 2018.