The post is updated with new information on a regular basis.

You arrive at the airport and forget to add your frequent flyer number to your reservation. Maybe you are flying for the first time, or maybe someone booked the flight for you. You didn't earn any miles on your flight.

You are not completely out of luck. You can retroactively claim miles for flights. You can do this even if you weren't a loyalty member.

It can be hard to claim these miles. There are many airlines that hide retroactive crediting. We will explain how to retroactively credit flights to the major U.S. carriers.

We want to walk through some of the best practices for traveling points and miles. These will make sure that you earn miles for your flights and give you leverage to request credit after the fact.

Sign up for frequent flyer accounts before you travel

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Before you travel, we recommend that you sign up for an account with the major airlines and hotels. It will be easier to get rewards when you head out of town if you don't have immediate plans to travel.

You can credit flights to these accounts. If you find yourself booked on a flight, you can earn United miles by adding your United Mileage Plus number to the reservation.

You should sign up for accounts with the Big 3 (American, Delta and United), as well as some of the budget carriers. A short list of things to do.

We recommend signing up for accounts with several hotels. These are the hotels you are most likely to see when traveling in the U.S.

You can sign up for our newsletter.

Refer to the account numbers on your phone when you book a flight or hotel room. You will never miss out on points and miles when travelling for work or fun.

Free points for new members are offered by loyalty programs.

Regularly conduct frequent flyer account audits

If you don't earn points in a given month, we recommend performing a monthly audit on all of your frequent flyer accounts. It protects you from fraud if you do this.

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It's easy to perform a mileage audit. Ensure the airline has posted the flights you took to your account by logging in to each of your accounts. All credit card spending, shopping portal purchases, dining rewards and other rewards should show up correctly.

You can retroactively claim miles if you see that you never earned them. If your bank does not have the correct frequent flyer number, you may need to call it.

Are you not able to see miles in your account immediately? Most airlines take at least 24 hours to post miles earned from flights to your account, but some are getting much quicker.

It can take longer if you credit a partner flight from one airline to another. It's time to request retroactive credit from the airline if you don't see a flight post to your account after a week.

If you don't have miles for a flight, what to do?

Save your receipts and boarding passes

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Save your boarding passes and flight tickets until the flight posts to your frequent flyer account. If you want retroactive flight credit, you will need information from these.

Save your digital boarding passes to your phone's wallet app so they don't disappear after the flight. You will want to save email confirmations with ticket numbers in order to credit miles after a flight.

Credit miles to an airline program.

Retroactive credit policies for each airline

It is time to request retroactive credit for your previous flights. Different airlines have different policies about this. Some airlines require you to claim credit after a certain period of time. Our earlier point about creating accounts ahead of time is even more important because others require that your account is open for a specific amount of time before you travel.

The details for the major U.S. airline loyalty programs can be found here. The link to the policy and how to request credit are included.

Alaska Airlines

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Alaska Airlines does not allow retroactive flight credit. You need to be a member at the time of travel to get mileage credit.

To request flight credit, go to this page on Alaska's website, fill out your information, and submit a copy of your boarding pass and ticket receipt Credit can be requested for both Alaska Airlines operated and partner flights.

You need to know what to look for.

  • When to submit: At least seven days after the Alaska flight date or 14 days after the partner flight.
  • Deadline for submission: Within 12 months of travel.
  • Need to be a member at the time of travel?: Yes.

American Airlines

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There is a little more lenience when it comes to retroactive flight credit. You need to enter your ticket number and AAdvantage number on American's flight credit request site.

You might not be able to request information online if you are missing miles from a partner flight.

The details are listed here.

  • When to submit: At least three days after the flight date for American-operated flights or 15 days for partner flights.
  • Deadline for submission: Within 12 months of travel.
  • Need to be a member at the time of travel?: No, but flights more than 30 days before your enrollment date are not eligible for mileage credit.

There's a way to claim missing American Airlines AAdvantage miles.

Delta Air Lines

ZACH GRIFF/THE POINTS GUY

Delta is similar to American Airlines in that it is easy to request mileage credit. Delta has a less strict policy on flights taken before enroll.

To request flight credit, log into your Delta SkyMiles account, click "view my skymiles," and then click "request mileage credit."

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If you follow these guidelines, you can submit your request for mileage credit from here.

  • When to submit: At least seven days after the flight date.
  • Deadline for submission: Within nine months of the flight date.
  • Need to be a member at the time of travel?: No, but the same nine-month submission window applies.

You can fill out the "All Other Miles Requests" form if you don't have a ticket. The trouble is worth it so you can later request mileage credit.

How to claim your Skymiles.

JetBlue

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A number of airlines have relaxed their policies for retroactively requesting mileage credit. You can claim mileage credit by logging in to your account and filling out the "Request Points" form. There are flights operated by partner airlines.

These criteria are used for these requests.

  • When to submit: At least 14 days after the flight.
  • Deadline for submission: Within 12 months of travel.
  • Need to be a member at the time of travel?: Not specified in the terms and conditions, so you should be able to request credit for all flights within the last year even if you weren’t a member at the time of travel.

Southwest Airlines

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Southwest has a credit policy. Go to the "My Account" screen if you want to request credit. You can request past flight points by clicking on the blue top bar.

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As long as you meet the requirements, you'll get credit.

  • When to submit: At least 48 hours after the flight.
  • Deadline for submission: Within 12 months of travel.
  • Need to be a member at the time of travel?: No.

United Airlines

ZACH GRIFF/THE POINTS GUY

We've finally got United. Signing in to your United account is required to request flight credit. Enter your ticket number at the bottom of the screen. The miles will be credited to your account if all is accepted.

The eligibility requirements are not easy to understand. There is a look here.

  • When to submit: At least five days after the flight for United or United Express flights, seven days after the flight for most partner airlines and 14 days after the flight for Virgin Australia.
  • Deadline for submission: Within 12 months of your flight date.
  • Need to be a member at the time of travel?: New members can request credit for United-operated flights taken up to 30 days before enrolling at no charge. You can also pay a $50 fee to claim credit for flights taken more than 30 days but less than six months before enrollment, though you'll need to submit a separate request.

Bottom line

There are a lot of reasons why you might need retroactive flight credit. If you weren't a member of a frequent flyer program at the time you traveled, you probably weren't.

Most U.S. airlines allow you to request mileage for flights taken up to a year before you enroll. You can request miles when they don't post, so keep a copy of your boarding passes.

The additional reporting was done by Ehsan.