The project start date, calendars, and default settings for calculating the schedule can all affect the way Microsoft Project schedules.

Project start date

By default, Microsoft Project schedules tasks to begin on the project's start date (a date you specify or the current date) and calculates the project's finish date based on the last task to finish. As you enter more information about tasks, such as task dependencies, durations, and constraints, Microsoft Project adjusts the schedule to reflect more accurate dates for tasks.

If you schedule a project from the finish date, Microsoft Project schedules tasks to finish on the date you specify and calculates the start dates based on the earliest task's start date.

Scheduling from the finish date can be useful for determining when a project must start if you have an immovable finish date. You can change various task and resource information to see what effect that information has on the project's start date and determine the optimum project start date.

Calendars

Calendars determine the standard working time and nonworking time, such as weekends and holidays, for the project. Calendars are used to determine resource availability, how resources assigned to tasks are scheduled, and how tasks themselves are scheduled. Project and task calendars are used in scheduling tasks, and if resources are assigned to tasks, resource calendars are used as well.

The calendars referred to in Microsoft Project are:

• Base calendars   They are the foundations for the other types of calendars. You can also choose a base calendar to be the project calendar, and you can apply a base calendar to tasks as a task calendar, or as the default hours for a resource calendar. Microsoft Project provides three base calendars: the Standard, 24-Hours, and Night Shift calendars. You can create your own base calendar by customizing any of the base calendars provided.
• Project calendars   They set the standard working and nonworking times for the project as a whole. If resource calendars or task calendars are not used, tasks are scheduled during the working time on the project calendar, by default.
• Resource calendars   They are based on the Standard calendar, by default. You can change working time or nonworking time for specific resources, or a set of resources, ensuring that resources are scheduled only when they're available for work. If you have changed working or nonworking time on a resource calendar and the resource is assigned to a task, the task is scheduled during the working time on the resource calendar.
• Task calendars   They can be used to define working times for tasks outside the working times in the project calendar. When a task calendar is assigned to a task and the resource assigned to the task has different working times in its resource calendar, the task is scheduled for the intersection of the two calendars' working times. However, you can set a task option to ignore resource calendars and schedule the task through the resource's nonworking time.

Default settings for calculating the schedule

Microsoft Project calculates the duration of tasks based on the definitions of the duration units on the Calendar tab of the Options dialog box (Tools menu). Just like a monthly calendar you use outside Microsoft Project, the year begins in January and each week begins on Sunday or Monday. When calculating duration units, one day defaults to eight hours, one week to 40 hours, and one month to 20 working days.

If you enter start and finish dates for tasks without start and finish times, Microsoft Project uses 8:00 A.M. as the default start time and 5:00 P.M. as the default end time.