A method of and system for handling allocation of task work to resources with flexibly configured availability contours (work calendars) is disclosed. The method includes defining one or more base calendars, a resource calendar associated with each resource, wherein the resource calendar inherits from a base calendar. A calendar reader, a set of recurring exception records, and a set of effective weeks for each calendar are also defined. For a specific date, the method determines whether an exception exists in one of the base calendar and resource calendar, and if an exception exists, computes a cached effective week honoring the exception data from an associated recurring exception record. If an exception does not exist, a cached effective week for the resource is computed from a combination of the calendar's standard week and associated effective week records.