What is the centre of vital interests and how is it established?

It decides matters where both states wish to tax under their domestic law. The double taxation treaty between Germany and Bulgaria then applies a staged test: first the permanent home, then the centre of vital interests, then habitual abode and finally nationality. The centre of vital interests is measured by verifiable circumstances: where the family lives, where the children go to school, where the accounts are held, where the family doctor is, where the car is registered, where professional and social ties lie. The sum of those circumstances decides, not any single feature. General information, not tax advice.