Do I have to declare my foreign assets when I move to Spain?

Once you become a Spanish tax resident — broadly, once Spain is where you spend more than half the year or hold your center of interests — you may need to file Modelo 720, the informational declaration of assets held abroad. It applies when any single category (foreign accounts, investments, or real estate) exceeds €50,000.

It’s informational — filing it doesn’t itself create tax — but skipping it carries real penalties, and the filing window is fixed: 1 January to 31 March for the previous year. If your foreign holdings are anywhere near the threshold, put it on your first-spring calendar before you move.