How to check in online for a United Airlines flight

With United Airlines, online check-in opens 24 hours before departure, on united.com or in the United app. When it closes is another matter. The deadline moves with your bags, with whether the flight is domestic or international, and with the airport you are leaving from.

Below we set out what you need before you start, how the process runs on the website and in the app, and what is left to do once you reach the airport.

Online check-in opens 24 hours before departure, and it works the same way on united.com and in the United app.

Closing is the part that needs attention. United Airlines sets a single deadline for being checked in and does not publish separate limits for the website, the app and the airport counter. What moves that deadline is your bags and where you are flying.

Those three limits are the general rule. If you miss the one that applies to your flight, your reservation may be canceled, and you may not be able to board or to check your bags. Many airports set their own limits, and those come next.

How early you can check a bag

There is a limit at the other end as well. For the most part, bags are not accepted more than four hours before departure. Counter hours also vary from airport to airport, so it is worth looking yours up before you plan an early start.

To start online check-in you need two pieces of information:

• your confirmation number, six characters, or your eTicket number, 13 digits. Both go in the same field;

• the passenger's last name.

Your confirmation number identifies your reservation and appears on your confirmation email. It goes by other names too, among them record locator, booking code and PNR, so you may see it called any of those. The eTicket number is on the receipt from your purchase.

If you have a MileagePlus account, you can sign in instead of typing either number.

Online check-in with United Airlines follows the same path on the website and in the app. Both start by pulling up your booking.

How to check in online with United Airlines:

1. Go to united.com/checkin, or open the United app and select check-in.

2. Enter your confirmation or eTicket number and the passenger's last name. With a MileagePlus account you can sign in instead of either number.

3. Select Continue and follow the steps through to the end.

4. Get your boarding pass, printed or on your phone.

You can check in on united.com or with the United app. Here's how each option works, including passport scanning in the app for international travel.

With a carry-on only and a boarding pass in hand, you can head for your gate. A checked bag is what still brings you to the counter.

There are three ways to hand one over:

• prepay for the bag on united.com or in the United app, then use the bag drop shortcut;

• print your bag tags at a kiosk, then take the bag to a United Airlines ticket counter representative;

• use curbside skycap, at the airports where it is offered.

Some airports do not take cash, so a card is the safer bet if you are paying on the day.

Getting to your gate on time

United Airlines recommends being at the gate 15 minutes before boarding starts on U.S. flights, and 30 minutes on international ones.

There is a second deadline behind that one: you have to be on board 15 minutes before departure time.

You checked in on time, your booking was confirmed, and you were at the gate when you were meant to be. A delay, a cancellation or an overbooked flight can still get in the way of your plans.

What you can claim depends on where the flight starts.

Flights within the United States come under Department of Transportation rules. There is no cash compensation for a delay or a cancellation. You are owed a refund if your flight is canceled or changed significantly and you turn down what is offered in its place. There is compensation if you are denied boarding because the flight was overbooked. Our guide to US air passenger rights sets out the detail.

Flights leaving an airport in the European Union are covered by EC 261, whoever operates them. If the airline is responsible, you may be owed up to $650 per passenger, depending on how far you were due to fly. United Airlines is not a European airline, so the rule runs one way only: Paris to New York is covered, New York to Paris is not.

To find out what your own flight may be worth, start with our United Airlines compensation page.

Keeping track of your United Airlines flight

Online check-in is done, but a flight can still change before departure. United Airlines publishes travel alerts, and recommends checking whether your flight is affected by one before you leave for the airport.

For another way to keep an eye on your flight, the free AirHelp app can track your flight and check whether a delay, cancellation or denied boarding may entitle you to compensation.

With the AirHelp app you can:

• receive real-time notifications about delays, cancellations, gate changes and baggage claim;

• scan your boarding pass to add your flight quickly;

• share your flight status with whoever is picking you up;

• find out automatically when you are owed up to $650 in compensation;

• start your claim straight from the app, with no paperwork.

The app is free and available on iOS and Android.