Oh, boy. It may be too late to start, if you don't know how to do it (yet). I have an English-speaking (from Ireland) "gestor" who does all mine for me. I'd be lost without him.

Since you're a US citizen but residing (with legal residency, as you are) abroad, you have to at least file a tax return in the USA and include your income from your Spanish endeavors. Not sure what the figure is now but if you make something like more than $110,000 you have to pay US income tax on the amount in excess of that. If below that amount, you don't have to pay tax but you do have to file a return.

As for Spain, you'll have to file a return here, of course, and pay income tax. I image you've been paying social security and all that too.

A retired US military guy near Madrid does my U.S. taxes for me, which is complicated as I have to include all my Spain-based business stuff too. If you want, I'll give you his number, but can't guarantee he's taking on new clients.

Saludos, MadridMan