The window for claiming "missing" or retroactive flight points varies by airline, but it generally ranges from 3 to 12 months after the date of travel. For instance, Delta SkyMiles and United MileagePlus typically allow claims for flights taken within the last 12 months, provided you were already a member at the time of the flight. If you were not a member when you flew, some airlines allow a shorter "grace period" (often 30 to 90 days) to join and claim those specific past miles. It is crucial to keep your boarding pass and "13-digit ticket number," as these are the primary pieces of evidence required to process a claim. In 2026, most major carriers have automated this via their mobile apps, allowing you to scan a barcode or enter a flight number to have the points credited instantly. If you are dealing with partner airlines (e.g., flying on Lufthansa but wanting United miles), the process can take longer and usually requires the flight to have been completed at least 15 days prior to the request.