A lot of people want Outlook’s calendar to work like a paper calendar – including the ability to X out “yesterday” to mark it complete.

Outlook doesn’t offer such an option but Outlook 2007 users can use color categories to mark events ‘completed’. Just create a Completed category and assign it a dark color. As you finish appointments, assign the Completed category - the calendar item picks up the color of the last category applied, which is Completed.

Or you can use a feature of Outlook 2007 that many people find annoying: when you apply a color category to an all day event that is marked busy or tentative, the background color for that date matches the color category. You can either create a new appointment and set it ‘busy’ or ‘tentative’ then apply the complete category or change an existing all day event and apply the completed category.

This screenshot shows All day events that are marked busy and use a color category with a black background. The category is called "Completed" and its assigned to the color Black. It also shows appointments assigned the "Completed" color category. These are black but the background is to colored because they are not All day events. (Tentative all day events have a shaded background.)

Recurring events can't be marked Complete using this method as its "all or nothing" - you can't assign a color category to just one item in a series.