Posted: Mon Dec 6, 2021 6:50pm
In simple terms, the Spanish tax authorities require you to inform them of any financial assets you hold outside Spain on midnight 31 December of each tax year, if over 50,000€ in any of three categories - all your bank accounts including savings accounts, property, stocks and shares of all types.
You do this via the modelo 720 form. Once you've done your first, you don't need to submit another unless your previously declared asset has increased by more than 20,000€, or you now have more than 50,000€ in a previously undeclared category.
Be aware that this info is to keep the tax authorities informed only, it doesn't lead directly to tax. However, they might get a bit suspicious if, for example, you say in modelo 720 you have £500k in shares, but don't declare any dividend income in your annual tax return!