I have a United flight CDG-RTB-CDG. Now I already used CDG-RTB, and I want to change the date of RTB-CDG, which my fare allows without fee with price difference only.

The problem is that it's a pain to find an alternative flight. For each day that I want to look up prices, I have to enter it manually, then wait for quite a while for results to come up, then click the sort-by-prices button in the list.

Is there another way to search for prices of return flights, maybe getting a table overview?

Easiest is actually to call Unitd and let them do the work. From experience agents can quickly find cheap alternatives. I wish I had their tools available.

What I'm doing right now:

  • Change dates in the URL with the results. That allows me to quickly change dates, but I still have to wait ages for results and then click the sort-by-price button.

  • Check one-way flights RTB-CDG on Google Flights. The cheapest ones there may be the ones I should consider as alternative return flights, but I'm not sure about that logic. And of course the flights on Google Flights are cached, so not necessarily accurate.

Update: When I called yesterday, the agent actually told me that she also has to look for flights one-by-one. So that was not much help, although I'm pretty sure that the agent that I called a few weeks ago did have an overview, because she could quickly tell me that the lowest price differences are on April 30 and May 8 at 151€. So, in the end I just used the interface by United, despite it taking several minutes to get each result. Now there was an option even cheaper than 151€ on April 30. I found a flight for 30€ that transits through Frankfurt (may hop off there).

  • A "Table View" ("Date Grid" on Google Flights) won't display flights from days in the past, like the first leg you've already taken from CDG to RTB. Grids show only future flights, and prices only for round trips. Because there's no way to guess if a low-cost RT will also yield a low-cost only-the-return leg, I think you have to speak to a United agent and ask what you'll pay for various dates you're considering, or if any specific days are cheaper for the RTB > CDG leg. Commented Apr 20, 2022 at 1:50

3 Answers 3


The exact answer here will depend on the exact "fare rules" of your ticket which obviously we don't have, but I'll go with the normal rules you'd see for most tickets on that route.

In general, when attempting to change a ticket like this AFTER the departure of the first leg, the prices that are used for the changed legs are those that were in place at the time when you first booked the ticket, which will generally be cheaper than the current fares.

When you do something like look on Google Flights, you're seeing "todays" prices, not those that existed when you first booked the ticket. It's possible these will be the same, but it's likely they won't be. By looking for "one-way" flights you're also seeing the prices for one-way flights, which are generally higher than the price for return flights that your ticket is most likely based on.

The only places that will be able to give you accurate pricing for a change is either United or (possibly) the travel agency that you purchase the ticket through - if it was purchased through a travel agency (and even then, the travel agency will likely need to work with United to work out the correct prices).

In theory, you could try using the "change flights" functionality on the United website, however the unfortunate fact is that this functionality is known to not always function correctly - it may not give you all options for flights, and may overprice what it does offer. As a result, this is generally not the recommended way to do it, especially for a ticket that includes at least 3 countries in it!

Which leaves you with only one option - call United. As you've said, their agents have access to systems that should be able to calculate the new prices relatively easily, although even then they can sometimes have difficulty pulling up the historic prices depending on the exact situation.

  • "the prices that are used for the changed legs are those that were in place at the time when you first booked the ticket" - prices for the return flight certainly fluctuate, at least for United
    – feklee
    Commented Apr 20, 2022 at 13:49
  • Not sure where the fluctuation came from. Maybe I just got incorrect info from the agents, i.e. they didn't give me the best price, or there was a misunderstanding. From plenty of checks on my own, prices are stable, and they are low. In fact, I could change the return flight of my roundtrip, which I booked maybe two months ago, from today to next week, at zero price difference. This is very good to know for the future.
    – feklee
    Commented Apr 30, 2022 at 15:49

I would try the following:

  • Find the fare class for your flight. It’s the first letter of the fare code.
  • Go on experflyer.com (no affiliation). The service requires a subscription, but there’s a 5-day free trial, no credit card required.
  • Go to flight availabilities, enter RTB-CDG, April 23rd, +/- 3 days, UA, fare class, show all dates in one screen.
  • You’ll get a list of flights for that fare class for a full week. Availability is shown as a letter (the fare class) and a digit (the number of available seats in that bucket, or 9 if there are more than 9). You want those which are not 0 (or possibly a higher number if you are several people travelling).
  • Things are a bit complex in your case because of the multiple connections, but UA actually return the same availability for all flights on the itinerary, so you can quickly scan through the results.
  • To switch to the next week, click on “refine search” and add 7 days (or use the calendar) and search again.
  • If you don’t find anything in that fare class, you’ll have to try other fare classes. You can leave the class field empty to get all classes, they are arranged more or less in decreasing price order (though it’s really more complex than that). You can also select a subset of classes to make things more readable and quick to scan.

For instance in today’s routing via IAH and ORD there’s availability down to K class, while tomorrow’s only goes down to W (which is 4 buckets higher than K). On Friday one routing is fully booked while the other only has availability down to V (one notch above W).

Once you’ve found something interesting, check on the UA site.

Fare rules are complex enough that this is not guaranteed to get you the best price, but it should be a step in the right direction. Hopefully!

Note for instance that your original fare could include restrictions such as a minimum or maximum stay, having to stay over a week-end, travelling only on certain days of the week, black-out periods, and more.

  • Thanks, Expert Flyer is certainly an interesting ressource! I can see availability and connections. However, how does it help me find the best prices? I cannot even find the flight that in the end I rebooked to via United for April 30 2022, 12:41: RTB-IAH (UA 2457), IAH-FRA (LH 441), FRA-CDG (LH 1030)
    – feklee
    Commented Apr 20, 2022 at 15:11
  • Ah, I restricted to UA only, but you can change that to select Star Alliance for instance, or UA and LH. It still doesn't show LH 441 for IAH-FRA, only UA 46 (or LH 7600 which is the same flight as a code share), but that seems normal as LH 441 departs at 3:45 PM while your previous flight UA2457 arrives at 4:35 PM. Are you sure of your routing?
    – jcaron
    Commented Apr 20, 2022 at 15:55
  • The way to find the best prices in general is to follow a two-step approach: look for the cheapest fares, then find flights with availability for those fares. In your specific case, I simplified it to start by searching for the same fare code as the original flight, though depending on the fare, it could be useful to find cheaper ones.
    – jcaron
    Commented Apr 20, 2022 at 15:57
  • Ouch. Make sure you double check the dates on your flights. I wouldn't be surprised if that cheap routing was with a veeeeeery long overnight layover in IAH.
    – jcaron
    Commented Apr 20, 2022 at 16:01
  • @feklee Just making sure you've seen the last comment
    – jcaron
    Commented Apr 20, 2022 at 16:58

You can presort with a tool like ITA Matrix https://matrix.itasoftware.com/search

Search for "one way", "calendar of lowest fares" and United as the airline (routing code "UA+").

If there are any dates that look better than others, you can start with these. For May this does not look promising:

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  • I assume they are the same prices as on Google Flights, as Google acquired ITA many years back. Also, from what I can tell, the prices don't correlate at all to the prices of a return flight.
    – feklee
    Commented Apr 20, 2022 at 13:48

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