Icelandair low fares from San Francisco to Europe for off-season travel are widely available for dates outside major holiday periods from late November into March 2019.
A good example of the kind of deals available to many cities is San Francisco to Amsterdam at $333 round trip for economy light fares, which include free seat selection and 10kg/22lb. carry-on bag, plus one under seat personal item.
Icelandair San Francisco SFO – Rekjavik KEF – Amsterdam AMS – KEF – SFO
Standard economy for $50 more each way includes one checked bag, more frequent flyer miles, lower change fee and option for Iceland stopover up to 7 days.