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I have worked a few hours as a self-employed and made a small profit (about £150). I also had a part-time job during the 2016-2017 tax year, in which I earned about £11600. I did not pay any income tax on my main income since my tax code for the year was NT.

I am now filing my tax return, and the calculation tools tell me I have to pay about £150 of income tax, which I have guessed is 20% of everything above the personal allowance (£600 above the £11000 from my main employment + £150 from my self employed activity).

I thought my main income would still be non taxable, and that I would I have to pay income tax on the profits I made when working as self-employed. I am a bit surprised to see that I eventually have to pay back that sum. Is it the case that receiving income both from a non-taxable employment and from self-employment cancels the benefits of the NT code for the main employment?

Many thanks for you reply.