If you are Resident this means you should be submitting Resident Income Tax Returns around May / June of each year, the deadline for these being 30^th June of any given year.

If you are a Non Resident property owner, or receive income from a Spanish Bank, then you should be submitting Non Resident Income Tax Returns around November / December of each year, the deadline being 31^st December of any given year, this last one obviously has nothing to do with your income.

Failure to do either could result in fines and interest being levied against you or your assets.