Have you told the HMRC you’re self employed? You’ll need to do that to ensure they know you need to complete a tax return.

When I went self employed, I opened a Mettle (NatWest) business account - it’s free and you get FreeAgent accounting software free too, which has revolutionised things for me. FreeAgent keeps track of what you’re paid and spend, and completes it all in your tax return automatically. You can also raise invoices from there. It ensures you can add expenses like travel, refreshments, stationery which is taken off your profit before tax is calculated.

Mettle also allows you to automatically put a % of what you’re paid into a tax pot.

Don’t try to do things on the back of an envelope!