This is what's shown in my Access help. Perhaps yours is different.
The following table lists examples of expressions that use the DateAdd function to add date and time values.
You can use these expressions in calculated controls (calculated control: A control that is used on a form, report, or data access page to display the result of an expression. The result is recalculated each time there is a change in any of the values on which the expression is based.) on forms, reports, and data access pages (data access page: A Web page, published from Access, that has a connection to a database. In a data access page, you can view, add to, edit, and manipulate the data stored in the database. A page can also include data from other sources, such as Excel.).
Expression Description
=DateAdd("d", -10, [PromisedDate]) Displays a date that is 10 days before the value of the PromisedDate field.
=DateAdd("m", 1, "31-Jan-03") Displays a date that is a month after 31-Jan-03, so the expression will evaluate to 28-Feb-03.
=DateAdd("m", 1, "31-Jan-04") Displays a date that is a month after 31-Jan-04, and since 2004 is a leap year, the expression will evaluate to 29-Feb-04.
=DateAdd("q", 3, [PromisedDate]) Displays a date that is three quarters after the value of the PromisedDate field; for example, if the value of the PromisedDate field is 18-Jun-03, the expression will evaluate to 18-Mar-04.
=DateAdd("h", 3, [ArrivalTime]) Displays a time that is three hours after the value of the ArrivalTime field.
You can use these expressions in a calculated field in a query.
Expression Description
DueDate: DateAdd("q", 3, [PromisedDate]) Displays in the DueDate field a date that is three quarters after the value of the PromisedDate field.
PickUpTime: DateAdd("h", 3, [ArrivalTime]) Displays in the PickUpTime field a time that is three hours after the value of the ArrivalTime field.
