How similar is Portuguese to Spanish, compared to Italian?

Answer 1

Portuguese is extremely close to Spanish in the written form. Not so close to Italian.

Answer 2

As a speaker of all three of these languages, I often say that Portuguese is like the child of Spanish and Italian. At times, I find the grammar and syntax to be closer to that of Spanish or even French, to be honest. Yet, almost always the pronunciation is closer to Italian than Spanish. I have knowledge of European and Brazilian Portuguese, and I can say that Brazilian Portuguese is definitely closer in pronunciation to Italian than Spanish. There are actually communities in Brazil that speak Italian as a native language, and there exists in the areas of Parana and Santa Catarina italo-brazilian communities which speak "Talian." Talian is an Italo-brazilian language based off of "Veneto", the Venetian dialect in Italy.

In my opinion, I'd say that European Portuguese is closer to Spanish than Italian just based on pronunciation. However, this is a stretch, as European Portuguese does not even sound that similar to Spanish. Yet, in text, all three languages are mutually intelligible (able to be understood with no formal studies in the other languages).