Costing applications — common mistakes

In exam questions, you will often be provided with direct material costs, direct labour hours and rates, and information to calculate a predetermined overhead absorption rate (OAR). You must be able to construct a job cost sheet, calculate the total cost of the job or batch, and then determine the profit or the required selling price based on a desired profit margin or mark-up. Pay close attention to the basis of overhead absorption (e.g., labour hours, machine hours).

Not exactly. Batch costing is best seen as a variation of job costing. While job costing deals with a single, unique unit, batch costing deals with a group of identical units. The cost collection process is very similar (accumulating costs for the 'order'), but batch costing has the additional step of calculating an average cost per unit within the batch, which is not relevant in job costing where the 'job' is the unit.

This is a common and valid point. Factory rent is an indirect cost or an overhead. It cannot be directly traced to a single job. That is why we use overhead absorption. We estimate the total overheads for the factory for a period and then divide this by an estimated activity level (like total labour hours) to get a predetermined overhead absorption rate (OAR). Each job is then charged a 'fair share' of the total overheads based on how much of that activity it used. This ensures all products bear a portion of the necessary indirect costs.

For the purposes of the AS Level syllabus, 'unit costing' often refers to the simple calculation of cost per unit in a single-product environment (Total Costs / Total Units). 'Process costing' is a more detailed method, typically covered later, used when products pass through multiple, distinct processes to be completed (e.g., mixing, then bottling, then packaging). While both aim to find an average cost per unit, process costing involves tracking costs for each process separately and dealing with concepts like work-in-progress, which is more complex than simple unit costing.