Which of the following is not part of prime cost of production?

Prime cost is the total of all direct costs that can be traced straight to the units of a product: direct materials, direct labour, and direct expenses. It excludes indirect costs (overheads), which are costs that support production generally but cannot be linked to a specific unit.

Direct expenses, the cost of raw materials, and carriage on raw materials are all direct costs that go straight into making the product, so each of these forms part of prime cost. Depreciation of factory equipment, however, is a factory (production) overhead: it is the gradual wearing out of machinery used across many units of output over time, and it cannot be traced to any single unit produced. It is added to prime cost only later, when calculating the total factory (production) cost.

A useful way to remember the distinction: prime cost answers "what did it directly cost to make this specific unit?", while overheads, including depreciation, answer "what did it cost to run the factory in general?".

In examination questions, treat any depreciation charge as a factory overhead, not a prime cost item, unless the question specifically asks for total production cost.