All three alliances with American, Delta, United and their partners are pricing Copenhagen and Stockholm under $500 round trip from San Francisco for travel August to October 2017.
Star Alliance has the lowest fares.
Lufthansa ticket for Swiss/SAS flights
San Francisco SFO – Zurich ZRH – Stockholm ARN – Zurich ZRH – SFO
American Airlines ticket for British Airways operated flights
San Jose SJC – London LHR – Copenhagen CPH – London LHR – SFO
KLM San Francisco SFO – Salt Lake City SLC – Amsterdam AMS – Copenhagen CPH – AMS – SLC – SFO