Auditing work-in-progress valuation means testing how far through the production process each WIP lot actually is, since cost build-up depends directly on that stage-of-completion estimate, verifying the bill of materials and routing used to cost it against what the production process genuinely consumes, and accepting that WIP cannot be physically verified with the same confidence as finished goods because a half-made component carries no finished specification to check it against. The valuation risk in WIP is concentrated in the estimate of completion stage, more than in the cost rates applied once that stage is fixed.
Why stage-of-completion is the central estimate
Finished goods valuation is largely mechanical once the cost formula is settled — a completed unit either exists or does not, and its cost is whatever the costing system says a completed unit costs. WIP valuation has an extra variable: how far through the process is this lot, and that variable is almost always a management estimate rather than a directly observed fact.
- A lot sitting between two production stages might be recorded as 50% complete by convention, regardless of which of the forty operations in the routing it has actually passed.
- Multiple sub-assemblies at different stages, consolidated into one WIP figure, hide the fact that the stage estimate for each sub-assembly may be wrong in different directions.
- A process with long-cycle, multi-week production (casting, curing, chemical processing) makes stage-of-completion genuinely hard to observe even by someone standing in the plant.
Where the business has an incentive to show a particular margin, stage-of-completion is an easy lever: moving a lot from 40% to 60% complete without any actual change in the physical process pulls cost — and profit — forward with no transaction that looks unusual on its own.
Testing the stage-of-completion estimate
- 01Understand how the client's system assigns stageAutomatically, from the last completed operation recorded against the lot in the ERP (more reliable), or manually, by a production supervisor's estimate at month end (needs more scrutiny).
- 02Walk the production floor during the countObserve actual WIP lots and compare their visible state — which operations are physically done — against the stage recorded for that lot in the system.
- 03Recompute cost for a sample using an independently assessed stageIf your own floor observation suggests a lot is at a different stage than recorded, recompute its cost at the stage you observed and compare the difference to the recorded figure.
- 04Look for a pattern across stages near period endA disproportionate concentration of WIP lots recorded at stages just high enough to look substantially complete, clustered right before the balance sheet date, is worth investigating further.
Testing the bill of materials and cost build-up
Once a stage is fixed, the cost assigned to it depends on the bill of materials (BOM) and the standard cost or routing behind it — the list of materials, operations and time that go into a unit at each stage. If the BOM used for costing does not match the BOM the production process actually follows, every WIP valuation built on it is wrong in the same direction, consistently.
| Check | What it catches |
|---|---|
| Compare the costing BOM to the current engineering/production BOM | A BOM revised for a product change but never updated in the costing module |
| Recompute standard cost per unit from raw material rates, labour rates and overhead absorption | A standard cost that was set once and never revised despite material price movements |
| Trace actual material consumption for a sample of production orders against the BOM quantity | Significant scrap or rework not reflected in the standard, understating true cost to complete |
| Confirm overhead absorption basis used for WIP matches that used for finished goods | An inconsistency that misallocates cost between the two categories without changing the total |
The physical verification problem
Finished goods have a specification: a completed unit either matches it or does not, and existence is straightforward to confirm by counting. WIP has no such fixed reference point, because by definition it is not yet in its final form, and an item that is half-machined does not have an independent description you can check it against the way you can check a finished unit against its part number.
- Physical count of WIP can confirm existence and a rough visual stage, but cannot independently verify the cost assigned, because the cost comes from the BOM and routing, not from an inspection of the item itself.
- Quantity counting is also harder: WIP often sits as bulk material mid-process (a vat, a furnace charge, a continuous line) rather than discrete countable units, and the client's own estimate of quantity in such cases needs to be challenged, not simply observed.
- Where WIP is a small part of total inventory, detailed procedures elsewhere (cost recomputation, BOM testing) typically carry more of the evidential weight than the physical count does.
Common practice, not a requirement
Record WIP observations at the count separately from finished goods observations, specifically noting the stage of completion observed for each lot examined and whether it is consistent with the system's recorded stage — this working paper is what the cost build-up testing relies on afterward.
How we think about this
Recomputing standard cost from material rates and labour rates, tracing the costing BOM against the production BOM, and tying absorption rates between WIP and finished goods are deterministic checks that belong in software, run against the full production order file rather than a handful of samples. Assessing whether a stage-of-completion estimate reflects what is actually on the factory floor needs a person who has walked the floor, and no system can substitute for that observation.
This is practical guidance written for audit teams, not an authoritative statement of any standard or statute. Standards, forms and timelines change. Check the current text issued by the ICAI and the relevant authority before relying on anything here in an audit file.
Related resources
- Inventory & stockInventory valuation audit: FIFO, weighted average and cost testingTesting the cost formula actually applied against the one disclosed, NRV testing, and overhead absorption into manufacturing cost.
- Inventory & stockAuditing standard costing variances in manufacturingMaterial, labour and overhead variance analysis under standard costing, and what each variance tells an auditor about inventory valuation risk.
- Inventory & stockPhysical stock count: audit observation procedurePlanning the count date and cut-off instructions, test counts and sampling, covering multiple locations at once, and reconciling count to book quantities.
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