The datepicker is a graphical user interface widget which allows the user to select a date from a calendar and/or time from a time range. The typical practice is to provide a text box field which, when clicked upon to enter a date, pops up a calendar next to or below the field, allowing the user to populate the field with an appropriate date, or provides a text box with an icon of a calendar such that when the icon is clicked on, the calendar (or time field) appears.
This example has a datepicker for the 'Start Date', an input for the 'Duration' (in weeks) and a second datepicker that is disabled for user input as it is updated on change of either the first datepicker or the duration inputs.