I have two citizenships, a different coutry of residence and I'm studying abroad. Where do I pay taxes?

Question

Background

• I have dual citizenship, Italian and Belgian
• My permanent residence is in (mainland) Spain
• I'm studying at a university in the UK (specifically, Scotland)

Question

I recently started to give private lessons through Superprof's UK website. As far as I understand, this work qualifies as being a sole-trader in the UK, or an autónomo in Spain.

When I started giving my first lessons, I was still in the UK and, I received some of the money in a UK bank account. In the meantime, I have moved back to Spain, and I continue giving lessons remotely.

To which country should I pay taxes? Both UK and Spain? Only Spain? All four (including countries of citizenship)? I'm confused.

My research

Navigating through the GOV.UK site, I've found this convention between the UK and Spain regarding double taxation. I'll highlight the fragments relevant to my case (all emphases mine). I'm quite the peasant regarding legal documents and law in general so I'm not confident about my interpretations.

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Article 4 defines the notion of "resident":

Article 4
RESIDENT

1. For the purposes of this Convention, the term “resident of a Contracting State” means any person who, under the laws of that State, is liable to tax therein by reason of his domicile, residence, [...]

[...]

2. Where by reason of the provisions of paragraph 1 an individual is a resident of both Contracting States, then his status shall be determined as follows:

   a) he shall be deemed to be a resident only of the State in which he has a permanent home available to him; [...]

If I understand correctly, under this definition I'm only a resident of Spain.

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Next, I tried to find an article which defined the terms for this particular kind of income, i.e. self-employed income. Article 14 only treats "Income from employment"; I don't know whether self-employment is included therein. Article 14 states (emphases mine):

Article 14
INCOME FROM EMPLOYMENT

1. Subject to the provisions of Articles 15, 17 and 18, salaries, wages and other similar remuneration derived by a resident of a Contracting State in respect of an employment shall be taxable only in that State unless the employment is exercised in the other Contracting State. If the employment is so exercised, such remuneration as is derived therefrom may be taxed in that other State.

This would mean I have to pay tax in both countries (?). Paragraph 2. mentions some cases in which taxes are only applied to the country of residence, but it mentions the term "employer" which again makes me suspect this article doesn't cover self-employment.

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Article 19 mentions students, but I don't think this applies since this income can't be considered to be solely "for the purpose of maintenance, education or training":

Article 19
STUDENTS

Payments which a student or business apprentice who is or was immediately before visiting a Contracting State a resident of the other Contracting State and who is present in the first-mentioned State solely for the purpose of his education or training receives for the purpose of his maintenance, education or training shall not be taxed in that State, provided that such payments arise from sources outside that State.

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Lest self-employment isn't covered in Article 14, I read Article 20 on "other income". (The remaining articles are titled "income from immovable property", "business profits", "shipping and air transport", "associated enterprises" "dividends", "interest", "royalties", "capital gains", "director's fees", "artistes and sportsmen", "pensions" and "government service", none of which are relevant, AFAIK.)

Article 20
OTHER INCOME

1. Items of income beneficially owned by a resident of a Contracting State, wherever arising, not dealt with in the foregoing Articles of this Convention, shall be taxable only in that State.

So, if my income qualifies as "other income", I would only pay tax in Spain (?).

Answer 1

I'm not familiar with the tax laws of this particular country pair, so take all of this with a grain of salt. However, the double taxation treaty is very similar to other such treaties between European countries that I do have experience with, so I'll make an educated guess for now.

Given the information you supplied, you are likely a Spanish tax resident.

Your income from self-employment doesn't likely fall under Article 14 at all, because that is for "real" employment where "income" equals wages/salary. According to Article 3 k), what you have is a "business income":

k) the term “business” includes the performance of professional services and of other activities of an independent character;

Your income should thus fall under Article 7 "Business profits" and be taxed in the UK (assuming that your self-employed activities take place only in the UK).

You may have to report that income also to the Spanish tax authorities as already taxed in the UK to avoid double taxation according to Article 22, but I don't know anything about the applicable Spanish income tax forms.