When do I need to do a tax return?

I started a new job in November 2018 which requires me to be self employed. I know the tax year runs from April to April. But I'm confused as to when I do this. Every month I've been getting paid I've been working out roughly what I'd get taxed on and been putting that into a separate bank... show more I started a new job in November 2018 which requires me to be self employed. I know the tax year runs from April to April. But I'm confused as to when I do this. Every month I've been getting paid I've been working out roughly what I'd get taxed on and been putting that into a separate bank account.
Would hmrc get in contact with me if and when they need it?
Thanks
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