In 2026, the most common reason a Delta flight is ineligible for SkyMiles is that it was booked as a Basic Economy (Basic) ticket. As part of their refined 2024 policy updates, Delta removed the ability to earn miles or "Medallion Qualification Dollars" (MQDs) on these lowest-tier fares. Other common reasons include: Award Travel (flights booked using miles do not earn additional miles), certain "deeply discounted" partner fares that do not have a mileage-earning agreement with Delta, or the ticket being a "non-revenue" or "agency" fare (such as those for airline employees or specific group tours). Additionally, if the name on your ticket does not exactly match the name on your SkyMiles account, the system may fail to credit the miles automatically. If you believe your flight should have earned miles, you have up to nine months in 2026 to request "Missing Mileage Credit" via the Delta website, provided you have your ticket number and boarding pass available. Always check the "fare class" (the single letter code) during booking to ensure it is eligible for rewards.