A comprehensive guide to United Airlines’ new same-day flight change policy

Editor's note: This is a recurring post, regularly updated with new information.

Not boarding the flight you paid for can sound like the start of a travel disaster — unless you use "SDC" as a verb.

That's short for "same-day change," an airline option to replace your original reservation with a new, confirmed reservation on a different itinerary to the same destination. Most airlines allow some form of this, often free for higher-tier elites, and it is worth learning their rules. But United Airlines' implementation stands out for its flexibility — especially if you know how to look beyond its app's same-day change suggestions. And starting Jan. 1, 2021, it's going to be available free of charge to all MileagePlus elite members.

Today we'll go through the ins and outs of what to expect the next time you need to make a last-minute adjustment to your United reservation.

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United's same-day flight change rules

United's policy for same-day changes is breathtakingly short by airfare-rule standards. The key things to know are:

• You and everyone on your reservation must be traveling on a domestic or international United ticket (with a number starting "016") on a United or United Express aircraft (although on my last international flight, United's app offered alternate UA-metal flights to get me to the same connection to a Brussels Airlines flight).
• The policy includes award tickets but not basic economy fares or certain bulk, group and consolidator tickets.
• You can request a same-day change starting 24 hours before your scheduled departure. You can change to a flight departing the day before or day after your original flight, so long as it's leaving within 24 hours from the time your request is made.
• Origin and destination airports must remain the same, but you can add or remove a connection. Unlike Delta, co-terminal swaps (i.e., switching from a flight out of Newark to a flight out of LaGuardia) are not allowed.
• You can same-day change if you checked bags so long as the change is completed at least 60 minutes before your new flight's departure.

Those rules already grant more choices than American (which yokes you to the original routing) and Delta (which doesn't let you drop a connection and limits same-day changes to flights within the U.S., Puerto Rico, the U.S. Virgin Islands and Canada).

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Fee for same-day flight changes

Non-elite travelers owe a $75 fee for confirmed same-day flight changes, but effective Jan. 1, 2021, same-day changes are free to Premier Silver, Premier Gold, Platinum, 1K and Global Services elites — making this a non-trivial advantage of even lower-tier United status.

You must also pay the fare difference if your original fare class isn't available. However, what United's site doesn't spell out — but which a FlyerTalk wiki does — is that you can usually avoid this. UA opens up many previously-closed fare classes by the time the same-day change countdown starts, and if you wait until a few hours before departure, even the cheapest fare buckets often reappear.

Related: The best credit cards for United Airlines flyers

Same-day change vs. standby

There are two types of last-minute flight changes: same-day flight change and standby. The key difference between a same-day change and waiting on standby for another flight is that same-day changes are confirmed changes, while standbys don't clear until shortly before departure. When standing by, you retain your original ticket in case a seat doesn't open up on your desired flight.

Beginning Jan. 1, 2021, all United customers will be eligible for free standby, eliminating the current $75 fee to confirm a standby seat. Flyers can add their name to the standby list up to 30 minutes before departure for domestic flights and up to one hour for international flights via United's app, website, or the airport.

Customers standing by are prioritized by Premier status level and the fare class originally purchased. Seats are automatically assigned to standby travelers. You'll typically only change your seat if your standby clears over an hour before departure.

Related: United permanently eliminates most change fees, adds free standby option

Searching for availability

United's app will usually offer same-day change options when you check-in and tap the "search other flight options" button. That will reveal alternate routings departing in the next 24 hours, with links to their seat maps and flight status that suggest your upgrade odds. This works after check-in, too; tap the "Trip Details" button on the home-page frame for your flight.

You can run the same search at United's desktop site (click the "Change flight" link on the reservation page), but the interface is a bit clunky and sometimes incorrectly shows change fees. You also may find fewer results during online check-in, so if you're going to use your computer, I'd suggest going in to manage your reservation. Finally, you're also able to explore same-day change possibilities at a check-in kiosk.

The website and app often don't capture the full cloud of same-day change probabilities. Instead, consult United's info-dense flight-status reports: Punch in your departure and arrival cities, then check seat maps and standby lists on each flight listed to find routings that should be available.

If you want to take it one step further, familiarize yourself with United's fare classes. While it may feel like you need a Ph.D. to do so, it will come in handy when you're trying to utilize the carrier's same-day change benefit.

By enabling Expert Mode on United's website or using ExpertFlyer's "Flight Availability" search feature (owned by TPG's parent company, Red Ventures), you should be able to see if your originally-ticketed fare class is available. If that flight option isn't offered in the app or online, you can be armed with that information when you call to request a change.

Related: Beginner's guide to award searches on ExpertFlyer

Remember also that the 24-hour same-day change time frame moves: If you want to stay an extra night somewhere, wait until that bracket shifts to include the next morning's flights. But time can be your enemy too: UA flights routinely fill up in the closing hours.

How to request a same-day change

If United's app or site doesn't offer your preferred routing, call its reservations line, tell the representative that you want to make a same-day change, and provide the flights you picked out when checking flights for your departure and arrival cities. If the agent says they can't make that work, thank them for their time, hang up and call again.

If the representative says you'll owe a fare difference, thank them for their time, hang up and call again in a few hours. Be aware that may not always work on popular nonstop routes like EWR-SFO unless you're okay with a middle seat.

You can also try direct messaging United's Twitter account or utilizing the new chat tool on United's app.

FlyerTalk and other reports suggest that requesting a same-day change from a check-in counter agent is your least successful and slowest option, so use this as a last resort.

Related: How to quickly reach an airline customer service agent

Useful scenarios

The traditional use case for making a same-day change involves a meeting wrapping up early and a desire to get home to your friends or family. It's also a nice security policy if a meeting runs late or you get stuck in traffic en route to the airport. However, mastering this opens up helpful possibilities beyond simply getting an earlier or later flight.

• On city pairs with multiple daily flights (i.e., DCA-ORD), you can book a cheaper flight at a non-ideal time, then take your chances on same-day changing to the flight you wanted.
• You can change to an aircraft with more legroom or better upgrade odds.
• You can drop a connection to save time.
• You can change your day's second flight while on your first flight--for example, if a westbound transatlantic flight will get into Newark or Dulles enough ahead of schedule for you to grab an earlier domestic connection.

Finally, since you can same-day change from a flight for which you've already same-day changed, you could theoretically repeat the exercise over multiple days. But we don't advise making this a daily habit.

How upgrades work with same-day flight changes

There was a time when United offered elites the ability to maintain confirmed upgrades when utilizing same-day change. However, this isn't the case anymore. Now, as is the case with other airlines, when you change a flight, you're moved back to your originally-ticketed cabin and added to the upgrade standby list at your applicable upgrade priority.

Related: The ultimate guide to getting upgraded on United Airlines

Bottom line

United's same-day change policy contains several quirks that make it unique among the major U.S. legacy carriers, but it's worthwhile to learn them. While the fee is waived for United elite flyers, there are many instances where it's worth incurring $75 and adjusting your trip within 24 hours of departure. Alternatively, if you have flexibility in your travels, all travelers will soon be able to standby for an earlier flight free of charge.

Additional reporting by Rob Pegoraro.