But if you forgot, it's OK. Most airlines, Keyes said, allow travelers to request miles three to 14 days after booking and within 12 months of travel.

Most major airlines, including American, Delta, and United, allow you to claim "missing miles" for a flight for up to 6 to 12 months after the travel date. For example, Delta typically allows requests for up to 9 months, while American Airlines generally permits claims for eligible flights within a 12-month window. However, you usually must wait at least 3 to 7 days after the flight is completed before the system will allow a manual claim. A crucial tip for new travelers is that many airlines also allow you to claim points for flights taken before you joined the loyalty program, usually within a 30-day window prior to enrollment. To claim your points, you will typically need your ticket number (a 13-digit code starting with the airline's specific prefix) and your flight details. It is always best to keep your boarding passes until you see the miles successfully posted to your account to ensure you have the necessary proof for a claim.