Project schedules a project from the information you enter about the following:

• The overall project.
• The individual work items (called tasks (task: An activity that has a beginning and an end. Project plans are made up of tasks.)) required to complete the project.
• If necessary, the resources (resources: The people, equipment, and material that are used to complete tasks in a project.) needed to complete those tasks.

If anything about your project changes after you create your schedule, you can update the tasks or resources and Project adjusts the schedule for you.

For each task, you might enter one or all of the following:

• Durations (duration: The total span of active working time that is required to complete a task. This is generally the amount of working time from the start to finish of a task, as defined by the project and resource calendar.)
• Task dependencies (task dependencies: A relationship between two linked tasks; linked by a dependency between their finish and start dates. There are four kinds of task dependencies: Finish-to-start[FS], Start-to-start [SS], Finish-to-finish [FF], and Start-to-finish [SF].)
• Constraints (constraint: A restriction set on the start or finish date of a task. You can specify that a task must start on or finish no later than a particular date. Constraints can be flexible [not tied to a specific date] or inflexible [tied to a specific date].)

Using this information, Project calculates the start date (start date: The date when a task is scheduled to begin. This date is based on the duration, calendars, and constraints of predecessor and successor tasks. A task's start date is also based on its own calendars and constraints.) and finish date (finish date: The date that a task is scheduled to be completed. This date is based on the task's start date, duration, calendars, predecessor dates, task dependencies, and constraints.) for each task.

You can enter resources in your project and then assign them to tasks to indicate which resource is responsible for completing each assignment (assignment: A specific resource that is assigned to a particular task.). Not only does this help you plan project staffing, it can also help you calculate the number of machines needed or the quantity of material to be consumed. If you enter resources, task schedules are further refined according to the following resource information:

• Work (work: For tasks, the total labor required to complete a task. For assignments, the amount of work to which a resource is assigned. For resources, the total amount of work to which a resource is assigned for all tasks. Work is different from task duration.)
• Units (units: The quantity of a resource assigned to a task. The maximum units is the maximum number of units available for the resource. For example, if you have three plumbers, the maximum units is 300 percent or three plumbers working full-time.)
• Working times (working time: Hours designated in a resource or project calendar during which work can occur.) entered in calendars (calendar: The scheduling mechanism that determines working time for resources and tasks. Project uses four types of calendars: the base calendar, project calendar, resource calendar, and task calendar.)

Other elements, such as lead time (lead time: An overlap between tasks that have a dependency. For example, if a task can start when its predecessor is half-finished, you can specify a finish-to-start dependency with a lead time of 50 percent for its successor [has a negative lag value].) and lag time (lag time: A delay between tasks that have a dependency. For example, if you need a two-day delay between the finish of one task and the start of another, you can establish a finish-to-start dependency and specify a two-day lag time [has a positive value].), task types (task type: A characterization of a task based on which aspect of the task is fixed and which aspects are variable. There are three task types: Fixed Units, Fixed Work, and Fixed Duration. The default task type in Project is Fixed Units.), resource availability (availability: Indicates when and how much of a resource's time can be scheduled for assigned work. Availability is determined by project and resource calendars, resource start and finish dates, or the level at which the resource is available for work.), and the driving resource (driving resource: The resource whose assignment to a task determines the finish date of the task.) can affect scheduling, so understanding the effects of these elements can help you maintain and adjust your schedule as needed.

When you create a new project, you first enter the project's start date. When you schedule a project from the start date, all tasks start at the project start date unless you specify otherwise.

With no task dependencies or constraints applied, the project's duration is the same as the duration of the longest task. In other words, the project finish date is the same as the longest task's finish date.

Task dependencies, such as the finish-to-start dependency between the first and second tasks (as shown here), can change the project's finish date.

Most projects should be scheduled from a start date. However, scheduling from the finish date can be useful for determining when a project must start if it must finish on a specific date. You can change various task and resource information to see what effect it has on the project's start date and determine the optimum project start date.

To specify whether you're scheduling from the start or finish date, and to specify what that date is, click Project Information on the Project menu.

Note  You must schedule a project from a start date or from a finish date; you cannot schedule from both start and finish dates. You pick which date you want to use (normally a start date), and Project schedules the other date (normally a finish date) for you based on the information you enter into the project plan.

When you need to control the start  (start date: The date when a task is scheduled to begin. This date is based on the duration, calendars, and constraints of predecessor and successor tasks. A task's start date is also based on its own calendars and constraints.) or finish date (finish date: The date that a task is scheduled to be completed. This date is based on the task's start date, duration, calendars, predecessor dates, task dependencies, and constraints.) of a task, you can change the constraint (constraint: A restriction set on the start or finish date of a task. You can specify that a task must start on or finish no later than a particular date. Constraints can be flexible [not tied to a specific date] or inflexible [tied to a specific date].) on the task. Flexible constraints (flexible constraint: A constraint that is flexible and does not tie a task to a single date. Flexible constraints are As Soon As Possible, As Late As Possible, Finish No Earlier Than, Finish No Later Than, Start No Earlier Than, and Start No Later Than.) work with task dependencies (task dependencies: A relationship between two linked tasks; linked by a dependency between their finish and start dates. There are four kinds of task dependencies: Finish-to-start[FS], Start-to-start [SS], Finish-to-finish [FF], and Start-to-finish [SF].) to make a task occur as soon or as late as the task dependency will allow. For example, a task with an As Soon As Possible (ASAP) constraint and a finish-to-start dependency will be scheduled as soon as the predecessor task finishes. By default, all tasks in a project scheduled from the start date have the ASAP constraint applied. Likewise, by default, all tasks in a project scheduled from the finish date have the As Late As Possible (ALAP) constraint applied.

Constraints with moderate scheduling flexibility will restrict a task from starting or finishing before or after a date you choose. For example, a task with a Start No Earlier Than (SNET) constraint for June 15 and a finish-to-start dependency to another task can begin June 15 if its predecessor is finished by June 15 (or later if its predecessor finishes after June 15), but it can't be scheduled before June 15.

With the default finish-to-start task relationship and an ASAP constraint applied to these tasks, the successor task (the second one) is scheduled to begin as soon as the predecessor task (the first one) is scheduled to finish.

With a SNET constraint applied, the successor task cannot begin before the constraint date, even if (as shown here) the predecessor task is completed before the constraint date.

If a task constrained to a date has a predecessor that finishes too late for the successor to begin on the date specified in the constraint, negative slack (slack: The amount of time that a task can slip before it affects another task or the project's finish date. Free slack is how much a task can slip before it delays another task. Total slack is how much a task can slip before it delays the project.) can occur.

To review or change the constraint on a task, select the task, click Task Information , and then click the Advanced tab. Constraint information is in the Constraint type and Constraint date boxes.

Deadline dates can affect total slack (slack: The amount of time that a task can slip before it affects another task or the project's finish date. Free slack is how much a task can slip before it delays another task. Total slack is how much a task can slip before it delays the project.) on tasks. If you enter a deadline date before the end of the task's total slack, total slack will be recalculated using the deadline date rather than the task's late finish date. The task becomes critical if the total slack reaches zero.

You can set deadlines for summary tasks (summary task: A task that is made up of subtasks and summarizes those subtasks. Use outlining to create summary tasks. Project automatically determines summary task information [such as duration and cost] by using information from the subtasks.) as well as individual tasks. If the summary task's deadline conflicts with any of the subtasks (subtask: A task that is part of a summary task. The subtask information is consolidated into the summary task. You can designate subtasks by using the Project outlining feature.), the deadline indicator signifies a missed deadline among the subtasks.

But deadline dates can affect how tasks are scheduled if you set a deadline date on a task with an As Late As Possible (ALAP) constraint. The task is scheduled to finish on the deadline date, though the task could still finish after its deadline if its predecessors slipped.

To review or change a task deadline, select the task, click Task Information , and then click the Advanced tab. Use the Deadline box.

The calendars referred to in Project are:

• Base calendars   These 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. Project provides three base calendars: the Standard, 24-Hours, and Night Shift calendars. You can customize your own base calendar using any of the base calendars provided.
• Project calendars   These 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   These 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   These 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 overlapping working time of the two calendars. But you can set a task option to ignore resource calendars and schedule the task through the resource's nonworking time.

To work with calendars, on the Tools menu, click Change Working Time.

If you don't assign resources (resources: The people, equipment, and material that are used to complete tasks in a project.) to tasks (task: An activity that has a beginning and an end. Project plans are made up of tasks.) in your project, Project calculates the schedule using durations (duration: The total span of active working time that is required to complete a task. This is generally the amount of working time from the start to finish of a task, as defined by the project and resource calendar.), task dependencies (task dependencies: A relationship between two linked tasks; linked by a dependency between their finish and start dates. There are four kinds of task dependencies: Finish-to-start[FS], Start-to-start [SS], Finish-to-finish [FF], and Start-to-finish [SF].), constraints (constraint: A restriction set on the start or finish date of a task. You can specify that a task must start on or finish no later than a particular date. Constraints can be flexible [not tied to a specific date] or inflexible [tied to a specific date].), and project and task calendar (calendar: The scheduling mechanism that determines working time for resources and tasks. Project uses four types of calendars: the base calendar, project calendar, resource calendar, and task calendar.) information. If you do assign resources, the tasks are also scheduled according to resources' calendars and assignment units (assignment units: The percentage of a work resource's time, or units, that the resource is assigned to a task.), providing for more accurate scheduling.

An assignment (assignment: A specific resource that is assigned to a particular task.) is the association of a specific task with a specific resource responsible for completing the task. More than one resource can be assigned to a task. Both work resources (work resource: People and equipment resources that perform work to accomplish a task. Work resources consume time [hours or days] to accomplish tasks.) and material resources (material resource: The supplies or other consumable items that are used to complete tasks in a project.) can be assigned to tasks. Unlike work resources, assigning material resources to a task does not affect task scheduling.

For example, in your project you have a task named Develop specifications. You also have an engineering resource, Sean. If you assign Sean to the Develop specifications task, the scheduling of this task depends on Sean's resource calendar and assignment units, in addition to task information such as duration, task dependencies, constraints, and calendars.

• The amount of work (work: For tasks, the total labor required to complete a task. For assignments, the amount of work to which a resource is assigned. For resources, the total amount of work to which a resource is assigned for all tasks. Work is different from task duration.) or overtime work (overtime: The amount of work on an assignment that is scheduled beyond the regular working hours of an assigned resource and charged at the overtime rate. Overtime work indicates the amount of the assignment's work that is specified as overtime work.) the resource is assigned to do, and how that work is distributed over time. Work distribution over time can also be affected by work contours (contour: The shape of how scheduled work for an assignment is distributed across time. Use a contour to control how Project schedules the work of a resource. Contour examples include flat, back-loaded, front-loaded, bell, turtle, and more.).
• The number of assignment units for the resource, that is, part-time, full-time, or multiple, on the task.
• The task type (task type: A characterization of a task based on which aspect of the task is fixed and which aspects are variable. There are three task types: Fixed Units, Fixed Work, and Fixed Duration. The default task type in Project is Fixed Units.), which affects how a schedule changes if you revise the existing assignment. The three task types are fixed unit (fixed-unit task: A task in which the assigned units [or resources] is a fixed value and any changes to the amount of work or the task's duration do not affect the task's units. This is calculated as follows: Duration x Units = Work.), fixed duration (fixed-duration task: A task in which the duration is a fixed value and any changes to the work or the assigned units [that is, resources] don't affect the task's duration. This is calculated as follows: Duration x Units = Work.), and fixed work (fixed-work task: A task in which the amount of work is a fixed value and any changes to the task's duration or the number of assigned units [or resources] do not affect the task's work. This is calculated as follows: Duration x Units = Work.).
• Whether the task is effort-driven (effort-driven scheduling: The default method of scheduling in Project; the duration of a task shortens or lengthens as resources are added or removed from a task, while the amount of effort necessary to complete a task remains unchanged.). If a task is effort-driven, as resources are added or removed on the assignment, the work remains constant for the task and is redistributed among the resources. For fixed-unit tasks, for example, one result is that if more resources are assigned, it will take less of a duration to complete the task.
• Resource calendars. Project schedules assigned resources based on working (working time: Hours designated in a resource or project calendar during which work can occur.) and nonworking times (nonworking time: Hours or days designated in a resource or project calendar when Project should not schedule tasks because work is not done. Nonworking time can include lunch breaks, weekends, and holidays, for example.) indicated on their resource calendars.

To assign resources to tasks, click Assign Resources .