You cannot add TSA PreCheck after check-in, but you can still use it on your next trip

Once you have checked in for a flight, TSA PreCheck cannot be added to that boarding pass. The security screening lane you use is determined at check-in, and the system does not allow changes after that point. However, if you already have an active TSA PreCheck membership, you should have received a Known Traveler Number (KTN) that you can add to future bookings before check-in.

If you checked in without adding your KTN and realize it too late, you will go through standard security screening on this trip. The good news is that adding your KTN to future reservations takes less than a minute and ensures you use the PreCheck lane on all upcoming flights.

Key Takeaways

  • TSA PreCheck benefits must be added during or before check-in, not after, because the security lane assignment happens at that moment.
  • Your Known Traveler Number (KTN) is a nine-character code provided when your TSA PreCheck membership is approved, and you need it to link PreCheck to your booking.
  • You can add your KTN when you book your flight, during online check-in, or at the airport ticket counter before standard check-in closes.
  • If you forget to add your KTN before check-in, you can still use TSA PreCheck on your return flight or any future flights by adding it during that check-in process.

Where to find your Known Traveler Number

Your KTN is a nine-character code that TSA sends you when your PreCheck membership is approved. It usually arrives in an email from TSA or appears in your TSA account online. Check your email inbox and spam folder for a message from TSA with the subject line containing "Known Traveler Number" or "KTN".

If you cannot find the email, log into your TSA PreCheck account at tsa.gov. Click on your membership status or account details, and your KTN should be displayed there. Write it down or take a screenshot — you will need it for every flight you book.

If you have an active membership but cannot locate your KTN anywhere, contact the TSA PreCheck enrollment center where you applied. They can confirm your membership status and resend your KTN by email.

How to add your KTN to future flight bookings

The easiest time to add your KTN is when you first book your flight. Most airline websites have a field labeled "Known Traveler Number," "Frequent Flyer Information," or "TSA PreCheck" during the booking process. Enter your nine-character KTN exactly as it appears in your TSA email, with no spaces or dashes unless TSA provided them that way.

If you booked your flight without adding your KTN, you can add it during online check-in, which usually opens 24 hours before departure. Log into your airline's website or app, find your reservation, and look for a section to add or edit passenger information. The KTN field is often under "TSA PreCheck" or "Known Traveler Information." Enter your number and save the changes before you complete check-in.

If online check-in has already closed or you prefer not to use it, you can add your KTN at the airport ticket counter before you check your bags. Tell the agent you have TSA PreCheck and provide your KTN. They will add it to your reservation and print a boarding pass with the PreCheck indicator. This must happen before the standard check-in process closes, which is usually 60 minutes before domestic flights.

What happens if you add your KTN too late

If check-in has already closed — either online or at the ticket counter — your boarding pass is locked and cannot be changed. You will go through standard security screening on this flight. TSA PreCheck is a benefit you use at the security checkpoint, not something that can be added retroactively once you have a boarding pass.

The security lane assignment is made the moment your boarding pass is issued. Even if you show your TSA PreCheck membership card or KTN to the security officer, they cannot move you to the PreCheck lane if your boarding pass does not have the PreCheck indicator printed on it.

On your return flight or any future flights, make sure to add your KTN before or during check-in. Setting a phone reminder when you book can help you remember to add it during online check-in 24 hours before departure.

Adding your KTN through different airlines

The process is similar across all airlines, but the exact location of the KTN field varies slightly. On American Airlines, United, and Delta websites, the field appears under "Passenger Information" or "Frequent Flyer Details" during booking or check-in. Southwest Airlines calls it "Known Traveler Number" and places it in the same section. Budget carriers like Spirit and Frontier also have a KTN field, though it may be labeled differently.

If you cannot find the field on your airline's website, call the airline's customer service line and provide your confirmation number and KTN. An agent can add it to your reservation over the phone. This is especially useful if you are traveling within the next few hours and online check-in is no longer available.

Preventing this problem on future trips

The simplest way to avoid forgetting your KTN is to add it to your airline frequent flyer profile. Most airlines allow you to store your KTN permanently in your account settings. Once it is saved there, it will automatically populate on every booking you make under that account, and you will not have to enter it each time.

To do this, log into your airline account, go to "Profile" or "Account Settings," and look for a section called "TSA PreCheck," "Known Traveler Information," or "Security Information." Enter your KTN once, and it will be applied to all future reservations automatically. This takes about two minutes and saves you from having to remember it for every trip.

You can also save your KTN in your phone's notes app or take a photo of your TSA PreCheck approval email. Having it easily accessible means you can add it quickly during online check-in if it was not automatically included.

What to do at security if your boarding pass does not show PreCheck

If you arrive at the security checkpoint and your boarding pass does not have the TSA PreCheck indicator, you will be directed to standard screening. You cannot use the PreCheck lane even if you show your TSA PreCheck card or membership letter. The security officer's screening assignment is based entirely on what the boarding pass says.

Go through standard screening as instructed. You will remove your shoes, belt, and light jacket, and place your laptop and liquids in a separate bin. It takes longer than PreCheck screening, but you will still make your flight. On your next trip, add your KTN before check-in to use the PreCheck lane.

Frequently Asked Questions

Can I use my TSA PreCheck card at security if my boarding pass does not show PreCheck?

No. The security officer uses your boarding pass to determine which lane to send you to, not your membership card. Even with a valid TSA PreCheck card, you must have the PreCheck indicator on your boarding pass to use the expedited lane. The indicator only appears if your KTN was added before check-in.

What if I do not know my KTN and my flight is tomorrow?

Log into your TSA PreCheck account at tsa.gov right away and look for your KTN in your account details. If you cannot find it, call the TSA PreCheck enrollment center where you applied — they can confirm your membership and email your KTN within a few hours. Once you have it, add it during online check-in 24 hours before your flight.

Do I have to add my KTN every time I book a flight?

No. If you save your KTN to your airline frequent flyer profile, it will be added automatically to every booking you make under that account. You only need to enter it once in your profile settings, and it will populate on all future reservations.

Can the airline add my KTN at the gate if I miss the ticket counter important date?

No. The gate agent cannot add your KTN or change your boarding pass at the gate. Your boarding pass is locked once check-in closes. You must add your KTN before the ticket counter closes, which is usually 60 minutes before domestic flights.

If I add my KTN after I checked in online, will it change my boarding pass?

No. Once you have completed online check-in and received your boarding pass, adding your KTN afterward will not update that boarding pass. You would need to cancel and rebook, which is not practical. Always add your KTN during the online check-in process, before you finalize it.