Maximizing Efficiency with the Machine Hour Method for Overhead Absorption

In a factory floor packed with CNC machines, injection moulding units, or automated packaging lines, workers contribute far less to production cost than the machines themselves. When overheads like power, depreciation, and maintenance are driven almost entirely by machine usage, dividing them equally across labour hours or units produced gives a distorted picture of what each job actually costs. This is exactly the gap the Machine Hour Method was designed to close, and it remains one of the most accurate tools in a cost accountant’s kit for absorbing factory overheads.

What is the machine hour method 🔗

The machine hour method absorbs factory overheads on the basis of the number of hours a machine (or a group of similar machines) operates, rather than on labour hours, units produced, or direct wages. The result is called the machine hour rate, and it represents the overhead cost recovered for every hour a machine runs. According to Finance Strategists’ explanation of the concept, the machine hour rate can be either an actual rate calculated after the period or a predetermined rate based on expected usage, and it is obtained by dividing the total cost to be absorbed by the number of hours the machine is operated or expected to operate.

This method is best suited to industries where machinery, not manual labour, drives production, think automobile component manufacturing, plastics processing, printing, and textile spinning mills. In such settings, overhead absorption based on machine operating cost is considered far more logical than spreading costs evenly across workers who may be doing little more than monitoring automated equipment.

Why link overheads to machine hours 🔗

Most overheads in a heavily mechanised cost centre exist because the machine exists, not because of the people around it. Depreciation, power consumption, repairs, insurance, and factory rent apportioned to that machine’s floor space all rise and fall with how much the machine is used. Tying overhead absorption to machine hours therefore creates a much closer cause-and-effect relationship between the cost incurred and the cost charged to a job or product.

Compare this to the labour hour method, which assumes overheads move with the number of hours workers put in. In a semi-automated plant where one operator supervises three machines, that assumption breaks down quickly. The machine hour method fixes this mismatch by treating each machine, or a homogeneous group of machines, as its own cost centre.

Setting up a machine as a cost centre 🔗

Before any rate can be calculated, every machine or group of identical machines must be established as an individual cost centre. This means all overheads connected to that specific machine, wherever possible, are traced and pooled separately instead of being lumped into one factory-wide overhead figure. Where a cost cannot be directly allocated to a single machine, such as factory rent or a supervisor’s salary covering an entire department, it is apportioned across machines using a reasonable basis like floor area or number of machines.

Classifying overheads: standing charges and running charges 🔗

Once the cost centre is defined, overheads relating to that machine are split into two categories, a distinction that cost accounting literature treats as fundamental to the method.

Standing charges (fixed costs) 🔗

These are expenses that stay constant regardless of whether the machine runs for one hour or ten. Common examples include:

• Rent and rates apportioned to the machine’s space
• Insurance premium on the machine
• Supervisor’s salary allocated to the cost centre
• Lighting and heating of the department

Running charges (variable costs) 🔗

These vary directly with how much the machine is actually operated. They typically include:

• Depreciation, when linked to machine usage rather than the passage of time
• Power and fuel consumed
• Repairs and maintenance
• Consumables such as lubricants and coolants

Some accountants prefer to treat depreciation as a standing charge when it is calculated on a straight-line, time-based method rather than a usage-based method. Either treatment is acceptable as long as it is applied consistently.

Calculating effective machine hours 🔗

The overhead pool alone is not enough. The denominator, machine hours, must also be worked out carefully. Total available hours in a period are reduced by idle time caused by breakdowns, routine maintenance, setup time, and holidays. As explained in a detailed breakdown of the allocation and apportionment process for machine hour rate, only these effective, productive hours are used in the final calculation, since idle hours do not generate any output to absorb the cost against.

The machine hour rate formula 🔗

Once standing charges and running charges are separately expressed as an hourly rate, they are added together:

Once this rate is fixed, overhead absorbed for any job is simply the actual (or standard) machine hours used on that job multiplied by the machine hour rate. A simplified illustration: if a machine’s standing charges for a month total ₹7,000, running charges total ₹14,000, and the machine operates for 700 effective hours, the standing charge rate works out to ₹10 per hour and the running charge rate to ₹20 per hour, giving a machine hour rate of ₹30 per hour. A job that uses that machine for 12 hours would absorb ₹360 of factory overhead.

Comprehensive machine hour rate 🔗

In highly automated processes, an operator’s role is inseparable from the machine’s operation, for instance, a single operator running a packaging line who must stay in sync with the machine’s speed throughout its cycle. In such cases, the operator’s wages are added to the simple machine hour rate to arrive at what is called the comprehensive machine hour rate. As CAclubIndia’s explanation of the distinction notes, this comprehensive rate gives a fuller picture of the true hourly cost of running that machine, including the labour that is functionally part of the machine’s operation.

Over-absorption and under-absorption 🔗

Since the predetermined machine hour rate is usually based on budgeted overheads and estimated hours, the amount absorbed rarely matches the actual overhead incurred at the end of the period. If actual machine hours run lower than estimated, overheads get under-absorbed, leaving a shortfall that must be written off or carried forward. If actual hours exceed the estimate, overheads are over-absorbed. AccountingTools’ explanation of absorption rates illustrates this with a straightforward example: when actual machine hours fall short of the hours budgeted, the shortfall in overhead recovery is charged as an expense in the current period. This reconciliation step is a routine but essential part of using any predetermined absorption rate.

Advantages of the machine hour method 🔗

This method is popular in mechanised industries for good reason:

• Accuracy: It reflects the actual cause of overhead cost far better than labour-based methods in machine-intensive settings.
• Fair job costing: Jobs that use machines longer are charged more overhead, and quick jobs are not overcharged.
• Useful for pricing and estimation: A reliable hourly rate helps in preparing quotations and setting standard costs.
• Highlights idle capacity: When fixed and variable rates are separated, the cost of idle machine time becomes visible, useful for capacity planning.

Limitations to keep in mind 🔗

The method is not without drawbacks:

• Additional record-keeping: Tracking machine hours for every machine or cost centre adds administrative work.
• Estimation difficulty: Forecasting machine hours accurately can be hard without a firm production schedule.
• Not universal: A single blanket rate across dissimilar machines produces misleading costs, so each machine group needs its own rate, adding to the workload.
• Ignores non-time-based costs: Some overheads are not proportional to running hours at all, and forcing them into this framework can distort results.

Where this fits in Indian industry 🔗

Sectors like automobile ancillaries, plastics and rubber processing, cement, and textile spinning rely heavily on this method because machine operating cost dominates their overhead structure. For students preparing for costing exams or entering roles in manufacturing finance, mastering standing and running charge classification, and the resulting rate calculation, is a practical skill that shows up directly in real factory costing systems, not just textbook problems.

What do you think? If a factory operates machines of vastly different ages and capacities within the same department, should it still use one composite machine hour rate, or does accuracy demand a separate rate for every machine? And how would you factor in unplanned downtime, like a sudden power cut, when estimating effective machine hours for the coming quarter?

References

1. https://www.financestrategists.com/accounting/cost-accounting/overhead-costing/computation-of-machine-hour-rate/
2. https://www.financestrategists.com/accounting/cost-accounting/overhead-costing/methods-of-factory-overhead-absorption/
3. https://www.yourarticlelibrary.com/cost-accounting/machine-hour-rate/machine-hour-rate-calculation-advantages-and-disadvantages/55664
4. https://theintactone.com/2019/10/27/allocation-and-apportionment-of-overhead-including-machine-hour-rate/
5. https://www.caclubindia.com/experts/difference-1503034.asp
6. https://www.accountingtools.com/articles/what-is-the-rate-of-absorption-in-accounting.html