1. A method for maintaining a calendar of a user, comprising: accessing an online profile of the user at a first social networking website; identifying, on the online profile, a first post referencing a physical location, wherein the first post is created on the first social networking website by a client application of the user on a first calendar date, and wherein the first post comprises a timestamp of the first calendar date; identifying, on the online profile, a second post referencing the physical location, wherein the second post is created on the first social networking website by the client application of the user on a second calendar date, and wherein the second post comprises a timestamp of the second calendar date; calculating, by a computer processor and based on the timestamp of first calendar date and the timestamp of second calendar date, a first time period between user visits to the physical location; estimating, based on the first time period between user visits, a future calendar date when the user is expected to visit the physical location; creating, in the calendar, an event scheduled to occur at the physical location and on the future calendar date; determining, after the future calendar date and based on the first social networking website and a second social networking website, that the user did not visit the physical location on the future calendar date; identifying, on the first social networking website, a third post referencing the physical location, wherein the third post is entered by the user on a third calendar date, wherein the third post comprises a timestamp of the third calendar date, and wherein the third calendar date is after the future calendar date; calculating a modified first time period between user visits based on the third calendar date; estimating, based on the modified first time period between user visits, a new future calendar date when the user is expected to visit the physical location; and creating, in the calendar, a new event corresponding to the new future calendar date.
8. The method of claim 1 , further comprising: creating, in the calendar, an indication that the event is tentative.