You'll want to consult a tax expert in Spain, no doubt. I for one wouldn't trust any financial info I got on a forum.

netmeg: I just need a starting point. Hearing other people's experiences is still good before visiting an advisor. I'm looking for a reliable one already, but how many of us 100% trust "experts", especially when it comes to lawyers and accountants? I personally don't, always had lame experiences.

@redbar: I simply don't see how your post relates to mine. Why are you trolling while you could just contribute by NOT writing, so anybody who could share some experience would have felt more comfortable. If you have NO IDEA how things work here in Spain, why make a USELESS post?

Hi professionalnoob - sorry I hadn't got around to replying to your private message. I am self employed in Spain and use an asesoria to deal with my tax, i guess you will need to do the same. I can't see that it would be a problem.

Thank you for the response. But are you also registered as an employee at a regular company? I understand it is like you say if you are only self-employed.

I am registered as self employed, not employed. I cant see that it would be a problem for you but you need to find an asesoria or hestoria to deal with it for you.
I guess your problem will be that in the time before you become employed, you will need to register as self employed, and pay social security at around 300 Euros per month. You will also need to do quarterly tax returns.
But you need propper advice.

Thank you for the input denisl. I am debating whether to keep the websites or simply sell them for like 3 years of expected Adsense income and forget about them totally. That's why I'm looking to figure out conditions that I would face if I do everything in Spain.

Again, thank you.

sell them for like 3 years of expected Adsense income

These days little publisher sites aren't worth the pixels they're printed.

Considering the chaos being caused by Panda and Penguin and sites getting dropped suddenly for no reason, even 1 years income is reasonable these days as you really can't expect anything beyond a year anymore unless you're a really big publisher like a newspaper, or something with a big brand unlikely to get dropped.

You may get your asking price, but be prepared for a 12 month revenue offer instead.

FYI, AdSense income is totally unstable because your site has no control over the ad prices or any direct influence over the advertiser. That's why I sell ads direct as well so I have a stable income base which could possibly get a 2x+ valuation just because it's more dependable.

YMMV

Hi professionalnoob, with all disclaimer possible my advise is that next year, May till July, when you will do your IRPF tax for 2014 add your Adsense 2014 income as an additional income as well you will do for your full time job salary.

Of course, ask for professional advise before do the IRPF tax.

Yeah! That's what exactly I was curious about: if it would be possible to declare it as "additional income", without any extra paperwork required on my side.

Thank you for your thought.