There are two key tax dates during October, affecting new landlords or self-employed people and also for those who want to file a paper tax return. The taxman will generate a unique taxpayer reference for you so you can complete a tax return. HMRC has a free online tool that helps you to check whether you need to submit a self-assessment tax return. 31 October - paper tax return deadlineOnce registered for self-assessment, there are two deadlines to be aware of, with one coming up soon. But anyone who has opted to complete a paper tax return must file it by the end of October.