Most airlines allow you to claim "missing miles" or "retroactive credit" for flights taken between 6 and 12 months prior to the request. The specific window depends on the airline's policy and whether you were already a member of their loyalty program at the time of the flight. For example, Delta and United generally allow claims up to 6 months after the flight, while American Airlines and British Airways allow up to 12 months. If you were not a member when you flew, the window is usually much shorter—often only 30 to 90 days—to encourage you to join. To make a claim, you typically need your ticket number and your boarding pass as proof of travel. It is a good habit to wait at least 7 to 14 days after a flight before filing a claim, as many systems take a week to process points automatically. Once submitted through the airline's website, the miles are usually credited to your account within 5 to 10 business days.