United and Continental both offer confirmed travel changes within certain time periods close to your scheduled travel times. On United, a bunch of conditions apply: -flight must be on United/United Express/Continental/Continental Express/Continental Connection metal -domestic flights only that are not part of an international itinerary this might no longer be true -must be on the same local calendar day as a scheduled flight (usually agents will be flexible about changing downline segments after the first one you're changing) -routing must remain the same (no coterminals or multi-airport city changes) for over the phone changes, connection cities can change at the airport -alternate flights must not be oversold and must have H fare availability -must make the request within three hours of the desired flight (it does *not* have to be within three hours of the scheduled flight) -$75 fee per person per direction for all changes you make at one time (aka, if you make one phone call to reservations and change a flight, you'll get charged, and then if you call again 20 minutes later to make another change, you should get charged again) -fee is waived for Global Services, 1Ks, Premier Executives, OnePass Presidential Platinums, Platinums, and Golds (and other passengers on the same PNR), Standard Awards, or fully refundable tickets -can be done by calling reservations, using Easy Checkin Online or Easy Checkin units at the airport, or with an agent at the airport, but there's more flexibility allowed at the airport -If you're planning on doing a confirmed change, I would hold off on checking in to your scheduled flights. If you're already checked in, changes at the airport are pretty easy. Changes through reservations will probably mean that they cancel your checkin, make the changes, then check you back in. -I'm pretty sure this doesn't apply if you're booked on another airline's code for a United flight (aka a US Airways flight number for a United operated segment) but again, an agent at the airport might be able to make anything happen -I'm pretty sure this does apply to United marketed, United operated flights booked on another airline's ticket stock -There's some ambiguity about what happens if you do a confirmed change that results in a fare break. Domestically, the maximum valid connection time is 4 hours. However I, and many others, have done confirmed changes that resulted in connection times of greater than 4 hours. Technically, this should cause a fare break that invalidates the ticket. In practice, this rarely seems to be an issue, and if an agent makes it an issue, try another agent. Examples (assuming availability): VALID: CLE-ORD-LAX can change CLE-ORD or ORD-LAX individually or CLE-ORD and ORD-LAX changed together CLE-ORD-LAX with CLE-ORD departing at noon local and ORD-LAX departing at 4pm local, if you request a change at 7am, you can change to a CLE-ORD departure between 7am and 10am (and if you desire an earlier ORD-LAX flight). If you request a change at 5pm, you can change to a CLE-ORD departure between 5pm and 8pm (and ORD-LAX connection) but this is pretty risky if there isn't availability because you might forfeit your ticket. SFO-IAD-RDU with SFO-IAD being a redeye at 11pm and IAD-RDU being the next day can change to SFO-IAD-RDU all on the same day departing SFO at 8am if they call between 5am and 8am. CLE-ORD-LAX can change to CLE-LAX or CLE-DEN-LAX at the airport only Maybe: FRA-ORD-SFO, might be able to change ORD-SFO NOT VALID: FRA-ORD-SFO cannot change to FRA-SFO or make a change to FRA-ORD SFO-ORD redeye departing at 11:45pm cannot change to SFO-IAD next-day departing at 6am ORD-IAD cannot change to ORD-BWI or ORD-DCA IAD-JFK cannot change to IAD-LGA or IAD-EWR Just because a change isn't valid doesn't mean that you won't be able to sweet-talk a reservations or airport agent into making the change for you. On high frequency routes, even if you can't change to the exact flights you want, you can still make a change to a better flight and then standby for the best flights. If you're trying to change to a later flight but still want a confirmed seat as a backup, you can do multiple changes. Say you're on an 8am flight and want a 9pm flight, at 7am you can change to a 10am flight, at 9am change to a noon flight, etc, etc, assuming availability is there and you've got the money to pay the many fees or have the fees waived. You're supposed to get rebooked in your original fare class (or H if your original coach fare class is unavailable but H is), but some agents have been known to make mistakes and rebook in other fare classes. http://www.united.com/page/article/1,,52142,00.html http://www.flyerguide.com/wiki/index.php/S*FAR/CONFIRM_SAME_DAY On Continental, different conditions apply: -Continental, Continental Express, Continental Connection, United, or United Express operated flights -Changes can be requested starting 24 hours before your originally scheduled flight and can be for a desired flight within 24 hours after you're making the request -Origin and destination airports must remain the same, however, connection airports can be changed if they still meet the routing rules of the purchased ticket -If the original ticketed fare class is available, only the same-day change fee is charged -If the original ticketed fare class isn't available, then in addition to the same-day change fee any additional amount (or refund) due to the changed fare is charged. Continental opens up fare bucket availability 12 hours before departure, so it might be worth checking again as you get closer to departure if at first you don't get an answer you like. -Fee is waived for Continental Presidential Platinums, Platinums, United 1Ks (including Global Services), Premier Executives, Golds -Fee is $75 for Silvers, Premiers, Premier Associates, and non-elites -Can be requested by calling reservations, checking in online, or with an agent or kiosk at the airport Examples (assuming availability): PBI-IAH-SEA leaving PBI at 10am on Friday. You can start calling in to request changes at 10am on Thursday until 10am Friday. I'm not really familiar with the CO side of things, so maybe someone else can help me flesh out this part. http://www.continental.com/web/en-US/content/reservations/samedaychange.aspx On both airlines, in addition to the advantages of having a confirmed reservation, making a confirmed change can increase the odds of getting an upgrade on the changed flights. Usually upgrade waitlists are cleared before standby waitlists and it is pretty rare to first clear standby and then clear an upgrade, but if you confirm the change then you are waitlisted with everyone who was already on the flight instead of waitlisted *after* everyone that was already on the flight. This is the pedantic side of me: there is no such thing as confirmed standby. Standby by definition is unconfirmed. There are confirmed changes.