The main limits for returns are €22,000 in respect of earned income which has already been subject to deductions, or investment income in excess of €1,600, or rental income (including imputed income) of more than €1,000. The limit is also €22,000 if you have more than one income, providing the total of the other incomes is less than €1,500. If it is more than €1,500 then the limit falls to €14.000 euros in 2019.
If you claim relief for double taxation, you need to file the RENTA income tax return, no matter the amount of income you receive.
There are benefits in submitting a return even if you are below these limits as it establishes your tax residence, which can be important in matters of capital gains, inheritance tax, copay prescriptions etc.
Or in the case that you worked on a temporary contract or contracts during the year, or part of the year, as you might be entitled to a return in those cases. Always worth your while to do a ‘borrador’ (draft) and check.