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. 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. 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.