Which Delta check in style suits you? Delta offers five check-in methods. For more details, read on, or visit the airlines website about Delta check in options: online, Delta mobile app, airport counter, airport kiosk and in select airports, curbside check in. Delta online check-in.You may check in to your flight up to 24 hours before departure, using the convenient Delta Airlines online. You can use online check-in to print boarding passes any time within 24 hours of your flight. At certain airports, you can go paperless and have an eBoarding Pass sent right to your smart-phone or other mobile device. When using online check-in, you go to the homepage of Delta Airlines website and select the Check In option.