If you forgot to add your Delta SkyMiles number to your reservation and some time has gone by, you may still be able to get mileage credit. You have nine months from the date of your flight to request mileage credit. Generally, miles for most Delta flights post within 24 hours of your flight.

Yes, you can claim "missing" Delta SkyMiles for flights you have already taken, but there is a strict time limit. In 2026, Delta allows you to request retroactive credit for flights up to 9 months after the travel date. This applies even if you weren't a SkyMiles member at the time you flew, provided you enroll and submit the request within that 9-month window. You must wait at least 7 days after the flight before submitting the "Mileage Credit Request" form on Delta's website or app. You will need your ticket number (a 13-digit number starting with 006), which can be found on your receipt or boarding pass. If you are trying to claim miles from 2024 or earlier, you are unfortunately out of luck, as the system hard-locks at the 9-month mark. For partner airlines (like Air France or KLM), the process is similar but may take up to 30 days to reflect in your account.