You are a tax resident in Spain if you spend more than 183 days here in a calendar year or if your center of economic interests is in Spain; in addition, you are presumed resident, unless you prove otherwise, when your spouse (not legally separated) and minor children live in Spain. The consequence is worldwide taxation: your Spanish income tax return covers all your income, wherever it is earned.
Sporadic absences count as days in Spain unless you can prove tax residency in another country, and the status applies to the whole year: Spain has no split-year residency. If two countries consider you resident at the same time, the tie is broken by the applicable double taxation treaty.
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