The new reporting requirements are part of a law passed last year by Spain's finance ministry and are aimed at cracking down on fiscal fraud.
The period for declaring these assets began on February 1st but only days now remain. The cut-off date is April 30th.
The declaration process can only be carried out online by completing the so-called Modelo 720 (720 form).
"The Modelo 720 is a new reporting requirement in Spain and is in addition to the existing reporting requirements. It applies to all Spanish tax residents, including the Spanish," Barry Davys, Partner at The Spectrum IFA Group in Spain told The Local.
"The form 720 is perhaps best described as a 'census'," said the financial advisor.
"It is not introducing any new taxes but it is designed to make sure that we all pay the taxes we should be paying."
"More specifically, the 720 is a requirement to report overseas assets. These are broken down into three categories: bank accounts, property and all other financial interests," he explained.
"Where the total assets in any one or more of these categories is more than €50,000, all assets in that category have to be reported. As an example, someone with three bank accounts with €20,000 in each account and another account with, say, €1, they will have to declare all four accounts."
The Barcelona-based financial advisor said that not all aspects of the reporting process were immediately obvious. He cited the requirement to report the purchase price of a property rather than its current value as being one such example.
He said his firm had been advising clients to take advice from suitably qualified accountants or lawyers to ensure the form is completely correctly.
The form itself is only in Spanish and an electronic signature is required to complete it.
If you do not yet have an electronic signature with the Ministry of Finance, you may not be able to obtain this in time. However, accountants and tax lawyers have access to electronic signatures which they can use to process your declaration.
The Ministry of Finance has a list of frequently asked questions (in Spanish) about the reporting requirements on its website.