What happened: You showed up at the gate a generous 45 minutes before departure, and the agent informed you that your flight was oversold. The airline asked for volunteers to give up their seats, but not enough people came forward, so you ended up missing the wedding you were traveling to.

What the airline should do for you: It’s all too common for airlines to overbook flights, in order to avoid getting stuck with empty seats from late cancellations and no-shows. But under U.S. law, as long as you checked in for the flight within the airline’s minimum time window — usually 30 minutes for domestic flights — and the aircraft you’re scheduled to fly on carries more than 60 passengers, you’re entitled to monetary compensation if you’re involuntarily bumped from your flight.

If you’re able to reach your destination between one and two hours after your originally scheduled arrival on a domestic flight or one and four hours later on international routes, the compensation is $200 or the face value of the segment you got bumped from, whichever is less.

If you’re delayed more than two hours (domestic) or four (international), the mandatory compensation rises to double the one-way fare, up to a maximum of $400. Although the airline may offer you a round-trip ticket as compensatio instead take the check because the tickets are issued in the same class as frequent-flier fares, which are often hard to book seats for.

Next time: Arrive at the check-in desk or automated kiosk an hour or more before departure. Airlines tend to bump starting with the passengers who check in last. You can check the Department of Transportation’s monthly reports at airconsumer.ost.dot.gov/reports for a look at other airlines’ oversale records. Your best bet is to call ahead to confirm your airline’s minimum time window for check-in.