Schengen Stay Planner is an iPhone app designed to assist travelers in planning their stays within the Schengen area. The app requires a subscription for full functionality, offering users the ability to calculate the available dates for staying in the Schengen area based on the 90-day stay rule within a 180-day period. Users are required to input all completed trips from the past 6 months and can also add future trips in any order.

Upon launching the app, users are presented with a calendar screen displaying available and unavailable dates for entering and leaving the Schengen area. The app allows users to input trips by selecting entry and departure dates, with options to create one-day trips and modify trip details such as the country of entry. All data is stored on the user's device and iCloud for seamless synchronization across devices.