Process costing explained: this guide covers what it means, who it applies to, the step-by-step process, documents required, fees, due dates and penalties in India — so you can stay compliant with confidence and avoid costly mistakes.
When output flows continuously through stages, such as mixing, grinding and packing in a paint unit, there is no job or batch to follow. Cost is collected per process and spread over the units that pass through. Two questions then matter: what happens to the cost of material lost on the way, and how do you value units that are only part-finished at month end?
Process cost per unit = (total process cost − scrap value of normal loss) ÷ (units input − normal loss units). Normal loss is expected and its cost is absorbed by good units; abnormal loss is avoidable and is valued like good units, then written off; abnormal gain is the reverse. Part-finished units are converted into equivalent units: units × percentage complete. Use it to value transfers and closing stock and to see where loss is higher than it should be.
Where process costing fits and the data needed
It fits continuous or repetitive production in stages: paints, chemicals, food processing, textiles, plastics. You need, for each process: units and cost of input, costs added in the process (material, labour, overhead), normal loss as a percentage of input (from experience), scrap value of loss, units transferred or completed, closing work-in-progress and its stage of completion. A costing and pricing analysis can build the process accounts from your stock and payroll records.
The method
- Open an account for each process: debit input, material, labour, overhead; credit normal loss (at scrap value), output and closing stock.
- Normal loss: expected, say 10 per cent of input; it is not a cost to be shown separately; its net cost is carried by good output.
- Abnormal loss: loss above normal; valued at the same cost per unit as good output; credited to the process and debited to an abnormal loss account; its scrap sale is credited to that account; the balance goes to the costing profit and loss account.
- Abnormal gain: output above expectation (loss less than normal); valued like good output; the gain is credited to the costing profit and loss account.
- Equivalent units for work in progress: equivalent units = physical units × stage of completion, calculated separately for material and for conversion cost (labour and overhead) if they are added at different stages.
Worked example, part 1: loss in Process I (mixing)
A paint unit's Process I takes 1,000 litres of base. Assumed figures: material ₹53,000, labour ₹18,000, overhead ₹12,000; normal loss 10 per cent of input, scrap value ₹20 a litre; actual output 860 litres.
- Total cost = 53,000 + 18,000 + 12,000 = 83,000.
- Normal loss = 10 per cent × 1,000 = 100 litres; scrap value = 100 × 20 = 2,000.
- Expected output = 1,000 − 100 = 900 litres.
- Cost per litre = (83,000 − 2,000) ÷ 900 = 81,000 ÷ 900 = ₹90.
- Actual output 860; abnormal loss = 900 − 860 = 40 litres.
| Process I account | Litres | ₹ | Litres | ₹ | |
|---|---|---|---|---|---|
| Material | 1,000 | 53,000 | Normal loss (scrap) | 100 | 2,000 |
| Labour | 18,000 | Output to Process II (860 × 90) | 860 | 77,400 | |
| Overhead | 12,000 | Abnormal loss (40 × 90) | 40 | 3,600 | |
| Total | 1,000 | 83,000 | Total | 1,000 | 83,000 |
Check: 2,000 + 77,400 + 3,600 = 83,000. The abnormal loss account takes ₹3,600 and receives the scrap sale of 40 × 20 = ₹800, so ₹2,800 is written off to the costing profit and loss account. Had output been 920 litres, there would be an abnormal gain of 20 litres, valued at 20 × 90 = ₹1,800; after setting off the scrap not realised on those 20 litres (20 × 20 = ₹400), ₹1,400 is credited to profit.
Worked example, part 2: equivalent units in Process II (grinding)
Process II receives 860 litres at ₹90 a litre from Process I (₹77,400). All figures assumed.
- Opening work-in-progress: 200 litres, fully through the previous process, 50 per cent converted. Its cost: previous process 18,000 (200 × 90) and conversion 3,570.
- Received this month: 860 litres. Conversion cost added this month: ₹37,350.
- Completed and transferred: 800 litres (including the opening 200). Closing work-in-progress: 260 litres, fully through the previous process, 50 per cent converted. There is no loss in this process.
- Check on litres: 200 + 860 = 1,060 = 800 + 260.
Weighted average method (opening stock is merged with the month's work)
| Previous process | Conversion | |
|---|---|---|
| Equivalent units: completed 800 + closing (260 × 100 per cent and 260 × 50 per cent) | 800 + 260 = 1,060 | 800 + 130 = 930 |
| Cost: opening + current | 18,000 + 77,400 = 95,400 | 3,570 + 37,350 = 40,920 |
| Cost per equivalent unit | 95,400 ÷ 1,060 = 90 | 40,920 ÷ 930 = 44 |
Completed 800 × (90 + 44) = 107,200. Closing WIP = 260 × 90 + 130 × 44 = 23,400 + 5,720 = 29,120. Total = 136,320, which equals the costs to account for (95,400 + 40,920 = 136,320).
FIFO method (opening work-in-progress is finished first, so only this month's cost is used for the rates)
- Equivalent units for this month: previous process = 600 started and completed + 260 closing = 860 (the opening stock needs no more previous-process cost). Conversion = 100 to finish the opening stock (200 × 50 per cent) + 600 + 130 = 830.
- Cost per equivalent unit: previous process 77,400 ÷ 860 = 90; conversion 37,350 ÷ 830 = 45.
- Completed 800 = opening WIP cost 21,570 (18,000 + 3,570) + finishing conversion 100 × 45 = 4,500 + 600 × (90 + 45) = 81,000, total 107,070.
- Closing WIP = 260 × 90 + 130 × 45 = 23,400 + 5,850 = 29,250.
- Total 107,070 + 29,250 = 136,320 ✓.
| Method | Transferred (₹) | Closing WIP (₹) | Total (₹) |
|---|---|---|---|
| Weighted average | 107,200 | 29,120 | 136,320 |
| FIFO | 107,070 | 29,250 | 136,320 |
What the owner decides. Process I lost 140 litres in all: 100 normal, 40 above. The ₹2,800 net cost of the 40 litres is a number to chase: a faulty valve, spillage, wrong dosing. Either WIP method is acceptable if used consistently; FIFO tracks current efficiency better when input prices move, and weighted average is simpler. Transfer cost into the next process and the stock value both rest on the equivalent-unit counts, so check the stage-of-completion estimates with the shop floor.
How to read the result
A rising abnormal loss shows a control problem, not a costing problem. The normal-loss percentage should be reviewed against actual losses once a year; setting it too generously hides waste. Costs of by-products and joint products arising in a process are taken up in the guide to joint products and by-products.
Common mistakes
- Treating abnormal loss as part of the cost of good output.
- Valuing abnormal loss at scrap value instead of at process cost per unit.
- Using one percentage of completion for material and conversion when material is added at the start.
- Mixing FIFO and weighted average from one month to the next.
- Forgetting that the cost of scrap sold is credited to the process (normal loss) or to the abnormal loss account.
The accounts feed the cost sheet for the product, and standard costs for process units are covered under material and labour variances.
Need help with process accounts?
If loss and part-finished stock are guesses in your books, we can help build process accounts and a monthly loss report through a costing and pricing analysis.
Key takeaways
- Process cost per unit = (total cost − scrap of normal loss) ÷ expected good output.
- Normal loss rides on good units; abnormal loss and gain are valued at process cost and taken to profit.
- Equivalent units = units × percentage complete, separately for material and conversion.
- Weighted average merges opening stock; FIFO values the month's work on its own cost.
- Use the same method every month.
Read next
- Joint products and by-products
- Cost sheet: prime cost to cost of sales
- Standard costing: material and labour variances
Disclaimer: The methods described are standard cost accounting and financial management techniques. The worked example uses an invented business and invented figures, including any tax, interest or exchange rate, which are assumptions for illustration and not current rates. Where the article refers to a legal requirement, the linked guide and the official text should be checked. This article is general information, not legal advice; check the official text before acting.