Performance Management · Accounting for environmental and sustainability factors

Input/Output Analysis and Material Flow Cost Accounting

Updated 11 October 2026 · Fact-checked

Input/output analysis tracks physical inputs and outputs and uses a mass balance (inputs = outputs, including waste) to find waste. Material flow cost accounting (MFCA) then values that waste at full cost, including materials, energy, labour and overheads, so hidden losses become visible and can be reduced.

Understand Input/Output Analysis and Material Flow Cost Accounting

Traditional accounting records costs by type, such as materials purchased. It often hides how much of a purchased material ends up as waste. Waste is buried in product cost or in overheads, so managers rarely see its true size.

Input/output analysis fixes this by tracking physical flows. You record every input (materials, water, energy) and every output (saleable product, waste, emissions, by-products). The mass balance rule says that what goes in must come out. Inputs = product outputs + waste outputs. If the numbers do not match, something is unrecorded, such as evaporation or leakage.

Material flow cost accounting (MFCA) goes one step further. It puts a cost on each flow. It splits the flows into positive product (what becomes saleable product) and negative product (waste and losses). The cost of the negative product includes the material that was wasted and also the share of energy, labour and overhead used to process it. These are costs the business paid for but got no revenue from.

MFCA is one of the techniques of environmental management accounting. It supports both cost saving and environmental aims, because less waste means lower cost and a smaller environmental impact. In the exam you may need to calculate waste, apply the mass balance, cost the waste and comment on how the information helps management.

Key rules to remember

Mass balance: Total inputs (by weight/volume) = Product output + Waste output; Use the same unit throughout. If the two sides differ, the gap is an unrecorded loss such as evaporation.
Waste quantity: Waste = Total input − Product output; Use this when waste is not given directly.
Cost split by weight: Cost of a flow = (Quantity of that flow ÷ Total output quantity) × Total cost of the stage; Usual approach in MFCA when processing costs are shared in proportion to physical quantity. Use it for material, energy, labour and overheads.
Cost of negative product: Negative product cost = Material cost of waste + Share of system costs (energy, labour, overheads); Shows the full cost of waste, which is much higher than the material cost alone.
Waste as a percentage: Waste % = Waste ÷ Total input × 100; Useful for comment and for comparing periods or processes.

How to solve Input/Output Analysis and Material Flow Cost Accounting questions

Use this order for any input/output or MFCA question. It keeps the numbers organised and shows the marker each step.

1Read the question and list every input and output with its unit. Convert to a common unit such as kg if needed.
2Check the mass balance: total inputs = total outputs. If waste is not given, calculate it as input minus product output.
3Identify the cost pools: material, energy, labour, overheads, and any waste disposal cost.
4Choose the basis for sharing the costs. Unless told otherwise, share by physical quantity of output.
5Calculate the cost per kg or per unit of output, or the percentage split between product and waste, for each cost pool.
6Add up the costs of the negative product (waste) and of the positive product (saleable output). Check that the two add to the total cost.
7Comment on the result: the size of waste cost, where waste arises, and what action could reduce it.
8State the final answer clearly with units and currency.

Quickest way: Percentage split method

When to use it: Use it when the question gives total input weight, product output weight and several cost pools, and asks for the cost of waste.

Find waste % = (input − product) ÷ input, or use the output split if the question gives it.
Add all the cost pools into one total for the stage, including the material cost.
Multiply the total cost by waste % to get the cost of the negative product.
Subtract from the total cost to get the cost of the positive product, and check it by calculation.
If the question asks for a cost per kg of good product, divide the positive product cost by the good output.

Common mistakes in Input/Output Analysis and Material Flow Cost Accounting

Costing waste at material cost only.
Students forget that energy, labour and overheads were also spent on material that became waste.
Fix: Apply the share of every cost pool to waste, not only the material. This is the whole point of MFCA.
Mixing units, such as litres with kg or tonnes with kg.
Data comes in different forms in the scenario and students rush.
Fix: Convert everything to one unit before you start the mass balance.
Failing to check the mass balance.
Students assume inputs equal outputs without testing it.
Fix: Add up both sides. If they differ, report the unexplained gap and say it needs investigation.
Sharing costs by the wrong basis.
Students use value or units instead of physical quantity.
Fix: Use weight or volume of output as the basis unless the question states another basis.
Treating by-products or recyclable waste as negative product with no adjustment.
Students ignore the question's information on sale or reuse value.
Fix: Read the scenario. If waste is sold or reused, show that income separately and comment on the net cost.
Giving a vague written comment such as 'waste should be reduced'.
Students do not link the numbers to action.
Fix: Name the stage with the most waste, quantify the cost and suggest a specific action, such as better quality control or a change of supplier.

Worked examples

Example 1

A process uses 10,000 kg of material costing ₹50 per kg. Product output is 8,500 kg and the rest is waste. Energy costs ₹30,000, labour ₹70,000 and overheads ₹50,000 for the process. Using MFCA with costs shared by weight, calculate the total cost of the negative product.

Show the solution

Waste = 10,000 − 8,500 = 1,500 kg.
Waste % = 1,500 ÷ 10,000 = 15%. Product % = 85%.
Material cost = 10,000 × ₹50 = ₹5,00,000.
System costs = ₹30,000 + ₹70,000 + ₹50,000 = ₹1,50,000.
Total cost = ₹5,00,000 + ₹1,50,000 = ₹6,50,000.
Negative product cost = 15% × ₹6,50,000 = ₹97,500.
Check: positive product = 85% × ₹6,50,000 = ₹5,52,500. ₹97,500 + ₹5,52,500 = ₹6,50,000.

Answer: The negative product costs ₹97,500. Of this, ₹75,000 is material (1,500 kg × ₹50) and ₹22,500 is system costs (15% × ₹1,50,000). Traditional records would show only the ₹75,000 material loss at best.

Example 2

A company puts 2,000 kg of input through a two-stage process. Stage 1 costs ₹4,00,000 in total (material and processing). 400 kg is lost as waste in Stage 1, leaving 1,600 kg. Stage 2 adds processing costs of ₹1,92,000 and loses another 160 kg, leaving 1,440 kg of finished product. Using MFCA, calculate the total cost of waste across both stages and the cost per kg of good product.

Show the solution

Stage 1 waste = 400 kg out of 2,000 kg = 20%. Cost of Stage 1 waste = 20% × ₹4,00,000 = ₹80,000.
Cost carried into Stage 2 = ₹4,00,000 − ₹80,000 = ₹3,20,000 for 1,600 kg.
Stage 2 total cost = ₹3,20,000 + ₹1,92,000 = ₹5,12,000 for 1,600 kg.
Stage 2 waste = 160 kg out of 1,600 kg = 10%. Cost of Stage 2 waste = 10% × ₹5,12,000 = ₹51,200.
Total waste cost = ₹80,000 + ₹51,200 = ₹1,31,200.
Cost of good product = ₹5,12,000 − ₹51,200 = ₹4,60,800.
Cost per kg = ₹4,60,800 ÷ 1,440 = ₹320.
Check: total cost put in = ₹4,00,000 + ₹1,92,000 = ₹5,92,000. Waste ₹1,31,200 + good product ₹4,60,800 = ₹5,92,000.

Answer: Total waste cost is ₹1,31,200 and the cost per kg of good product is ₹320. Stage 1 has the larger loss, so effort to cut waste should start there.

Exam tips

Show the mass balance first, even if it is a one-line check. It earns method marks and catches input errors.
When asked for the cost of waste, include all cost pools, not only material. Say so in your answer.
Do the check that positive plus negative product costs equal total costs. It takes ten seconds and proves your answer.
In written parts, link figures to action: which stage, how much, and what to change. Mention both cost saving and environmental benefit.
In Section A or B objective questions, read the unit and basis carefully. Options often include the material-only waste cost as a wrong answer.

Practice questions from Accounting for environmental and sustainability factors

Input/Output Analysis and Material Flow Cost Accounting: frequently asked questions

What is input/output analysis in ACCA PM?

It is a record of the physical inputs and outputs of a process, based on the mass balance that inputs equal outputs. It shows how much material, energy or water becomes waste. It is the first step before costing the waste.

How is MFCA different from normal cost accounting?

Normal costing often hides waste inside product cost or overheads. MFCA tracks physical flows and splits costs into positive product and negative product. The negative product is costed with its share of materials, energy, labour and overheads.

What basis do I use to share costs in MFCA?

Use the physical quantity of output, such as kg, unless the question gives another basis. Apply it to every cost pool so that waste carries its fair share of processing costs.

What if inputs and outputs do not balance?

The difference is an unrecorded loss such as evaporation, leakage or measurement error. In the exam, state the gap and say it needs investigation, as it may be a cost or an environmental risk.