Airlines' sales usually start on Monday and end by Thursday.
The least expensive flights are on off-peak days: Tuesday, Wednesday and Saturday.
The first flights on Saturday morning may be the cheapest.
The costliest takeoffs tend to be Sunday afternoon (when leisure travelers fly home) and Monday morning (when business travelers head back to the office).
If you are planning a long weekend away, consider flying out on Saturday and returning on Tuesday (highest fares are usually for Thursday through Sunday itineraries).