The cheapest days to book flights may be different from one week to the next, and the same is true for the day you travel.

Southwest Airlines tickets can now be purchased on Expedia-owned websites. This partnership marks a significant shift for Southwest, which previously only allowed bookings through its own platforms.

For example, if flights between San Diego and Hawaii usually cost around $450, the Flight Deals tool will only highlight that route when the fare drops to $360 or less. Here’s how it works ...