The actual overhead refers to the indirect manufacturing costs actually occurring and recorded. These include the manufacturing costs of electricity, gas, water, rent, property tax, production supervisors, depreciation, repairs, maintenance, and more.
The applied overhead refers to the indirect manufacturing costs that have been assigned to the goods manufactured. Manufacturing overhead is usually applied, assigned, or allocated by using a predetermined annual overhead rate. For example, a manufacturer might estimate that in its upcoming accounting year there will be $2,000,000 of manufacturing overhead and 40,000 machine hours. As a result, this manufacturer sets its predetermined annual overhead rate at $50 per machine hour.
Since the future overhead costs and future number of machine hours were not known with certainty, and since the actual machine hours will not occur uniformly throughout the year, there will always be a difference between the actual overhead costs incurred and the amount of overhead applied to the manufactured goods. Hopefully, the differences will be minimal at the end of the accounting year.