HMRC deadline as £100 fines start tomorrow nightThe first major deadline of the year is hours awaySelf Assessment tax returns explainedTaxpayers who have yet to file their self-assessment return for the last tax year are being reminded that they face an initial £100 fine on Saturday night. This year's deadline is the end of the day tomorrow, January 31. Filing now will give you peace of mind that your tax return is completed and if you have tax to pay, you have a week to arrange payment. For late filing, you’ll receive an initial £100 penalty, and after three months, you’ll be charged an extra £10 every day. “If you can’t afford to pay the full amount, then contact HMRC to set up a payment plan.