Manufacturing overhead is estimated and assigned to work in process and to specific jobs on an estimated bases through a predetermined overhead rateThis rate is established by the beginning of the year and is based on the relationship between estimated annual overhead costs and expected annual operating activity. This relationship is expressed in terms of a common activity base such as direct labor costs, direct labor hours, machine hours, or any other measure that will provide an equitable basis for applying overhead costs to jobs.The predetermined overhead rate. The formula for a predetermined overhead rate is shown below.