Norwegian Airlines has Los Angeles or Oakland to Stockholm for $307 round trip beginning in October 2017 when ticket prices drop to $170 one way to Stockholm and $137 one way from Stockholm to LAX or OAK. $200 LAX-ARN ticket prices are available on a few dates in September for $337 round trip.
Low fare $137 are available in August to December from Stockholm. This can be a cheap way home from a one-way frequent flyer award to Europe.
Prices rise $45 to $90 each way, if you want a self-selected seat assignment and/or checked bag. I have made four one way trips on Norwegian since December with no additional seat or bag fees. Only got stuck in a middle seat one time and no problem with carry on only bags.
Norwegian Airlines Los Angeles LAX – Stockholm ARN
$169.90 USD one way Tue October 10
Norwegian Airlines Stockholm ARN – Los Angeles LAX
1199 SEK ($137 USD) one way Thu October 19
$307 round trip Los Angeles LAX – Stockholm ARN.
Norwegian Airlines Oakland OAK – Stockholm ARN
$199.90 USD one way Fri Sep 15
Norwegian Airlines Stockholm ARN – Oakland OAK
1199 SEK ($137 USD) Monday Sep 25
$337 USD round trip Oakland – Stockholm ARN.
