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Work in Progress (WIP): What It Is, and Why Too Much of It Hides Problems
Work in progress, or WIP, is everything part-way through production: no longer raw material, not yet a finished product. It is one of the three inventory stages, and on a lean line it is watched closely, because a build-up of WIP usually points to a problem somewhere upstream.
Why does work in progress matter?
Work in progress ties up cash, floor space and labor in products that cannot yet be sold, so the more of it there is, the longer the lead time and the slower the cash comes back. Too much WIP also hides problems like bottlenecks and unbalanced lines behind stacks of half-finished product. Keeping WIP low is a core lean goal because it makes those problems visible fast.
Where does WIP sit between raw materials and finished goods?
Inventory moves through three stages, and WIP is the middle one:
- Raw materials: bought and received, but not yet used in production.
- Work in progress: on the line, partly built, tying up cash and space.
- Finished goods: complete and ready to ship or sell.
- WIP is the only stage that is adding labor cost while it waits.
Why does high WIP signal trouble?
Lean thinking treats WIP as a symptom. A build-up of half-finished product between stations usually means an unbalanced line, a bottleneck, or a downstream stop, and the bigger the pile, the longer the lead time. Pull systems and FIFO keep WIP low on purpose, so problems surface fast instead of getting buried under inventory.
The three inventory stages at a glance
Where WIP sits, and what it costs you.
| Stage | What it is | Main cost |
|---|---|---|
| Raw materials | Inputs, untouched | Cash tied up |
| Work in progress | Partly built, on the line | Cash plus labor, plus hidden problems |
| Finished goods | Complete, ready to ship | Cash and storage |
Related Terms
- Pull Production – keeps WIP deliberately low.
- Bill of Materials (BOM) – defines what each WIP unit needs.
- Batch Production
- Push Principle
