A long, long time ago if your meeting ended early or the wedding reception ran late, or there was a jackknifed tractor trailer on the 10 and you wanted to take an earlier or later flight on your original travel day, you could do so for free on a standby basis.
Those days are gone.
Now, airlines charge a fee for same day changes, and most no longer allow non-confirmed standby for earlier or later flights. Instead, you're now required to pay a fee for a confirmed same day ticket change, and that fee has gone up since the last time Airfarewatchdog.com checked.
American and United have increased their fee from a previous $50 to $75 and jetBlue now charges $50 instead of $40.
To their credit, however, both AirTran and Frontier lowered their fees for this service by about $25 per segment and Delta still charges "just" $50 for what used to be free.
Virgin America charges $25 to $50 depending on the route length. And jetBlue doesn't charge at all if you standby for the flight immediately preceding your original flight on the same day.
We've updated our handy chart showing the same day change rules for most U.S. airlines along with exceptions to the rules and other requirements here.