The best calendar apps for iPhone offer a range of features such as customizable views, notifications, integrations with other apps, and advanced scheduling tools. The top picks include Apple Calendar, which is simple and easy to use but lacks advanced features; Fantastical, a powerful app that offers natural language event creation and 16 widgets; Google Calendar, which seamlessly integrates with the entire suite of Google products; Microsoft Outlook Calendar, which brings work email and calendar together in one spot; Timepage, a beautifully designed app with a busyness heatmap; and Calendars 5, a dedicated app for every Apple device that offers exceptional usability across all devices. The best calendar app for iPhone depends on individual needs and preferences.