as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
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understand taxes when geting money from a project built long time ago plus my full time job
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you need to register as self-employed with hmrc (it is perfectly fine to be self-employed and employed by an employer at the same time, in exactly your kind of situation). then, when the income arrives you will need to declare it on your yearly tax return.  hmrc information about registering for self-employment and declaring the income is here: https://www.gov.uk/working-for-yourself/overview there's a few extra hoops if your clients are outside the uk; the detail depends on whether they are in the eu or not. more details about this are here: https://www.gov.uk/online-and-distance-selling-for-businesses/selling-overseas .
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