I haven't checked the maths but yes, that sounds right. I'm not sure what you mean by "over the threshold"? You only need to do a declaration if your wealth outside Spain is over the threshold but you declare the actual value. When i did mine the threshold for declaration was €50,000. The value (purchase price) of my house in the UK was £60,000. So my 720 declared my foreign assets at the then euro equivalent of £60,000. Not the difference between the two.