(Mods: Feel free to move this if there’s a good thread it should belong in)

Ran into an interesting residual value calculation on United’s website.

Went to go change the return leg of an in-process itinerary from EDI-ORD to LHR-ORD and pull up the date a few weeks (my son is able to come home from Uni earlier).

When united.com went to calculate the fare differential, it used the *entire* ticket value and not just the return leg.

Feels like this is an error in my favor and am curious if this is common or I just lucked out.