Does it cost to facetime abroad? In this case from Sweden to USA?

Does it cost to facetime from one country to another? In this case from Europe to USA, but does it matter? And yeah, does it cost to facetime abroad? And if it doesnt, is it just free when you facetime and both users are on Wifi or is it free if both users arent on wifi either? And also if its free is it free if one user is on wifi and the other on carrier abroad? Basically like, what way can u make facetiming abroad free? And does it matter what continent to what continent?

Would appreciate answers on as many questions as possible. Thanks