Yes, you can still cancel a flight after you have checked in online, but you must usually "undo" or "reverse" the check-in first. Most 2026 airline apps and websites have an "Uncheck" or "Cancel Check-in" button. Once your status is reverted to "booked," you can proceed with the standard cancellation or flight change process. If you cannot find the button, you will likely need to call the airline’s customer service or speak to a gate agent. It is important to note that checking in does not change the refundability of your ticket; if you have a non-refundable "Basic Economy" fare, you will still only receive a credit (minus fees) or nothing at all. If you wait until the very last minute (usually within 30–60 minutes of departure), you may be marked as a "No-Show," which often results in the total forfeiture of the ticket value, so it is best to cancel as early as possible.