What is vendor-managed inventory?
Vendor-managed inventory, or VMI, is an arrangement where the supplier takes responsibility for monitoring your stock levels and replenishing them, rather than waiting for you to place an order. They hold the replenishment decision. You still hold the requirement, the specification and the budget.
In practice someone at the supplier, or a system they run, knows what is on your shelf and what you have been using, and acts on it without being asked. The buying office stops raising routine orders and starts checking that the arrangement behaves. Done badly it moves the guesswork from your side of the fence to theirs and adds a delay.
- The supplier decides the replenishment; you keep specification and budget control.
- VMI only works where the supplier can see genuine consumption data.
- Forward information about mobilisations is worth more than historic usage.
- VMI is about who replenishes; consignment is about who owns the stock.
- Measure stockouts and stock turns, not whether the visit happened.
How VMI works day to day
The shape varies with scale, the sequence does not. Levels are agreed per item and location, consumption is visible to the supplier by some agreed route, and replenishment happens without a purchase order being raised each time.
- At the light end, a rep walks the stores on a fixed day, counts and tops up to agreed levels. That is imprest with the supplier holding the pen.
- In the middle, issues are scanned or logged as they leave the store and a report goes to the supplier weekly.
- At the heavy end, controlled-issue cabinets or vending units report draws automatically, so replenishment is triggered by consumption rather than by a visit.
Invoicing is usually consolidated: one invoice per period against a blanket order. That change alone is often worth more to finance than the stock benefit is to the stores.
VMI only works if the supplier can see real usage
Handing over replenishment without giving visibility of consumption just moves the guesswork. A supplier with no usage data holds a comfortable buffer, and either you pay for it in the rate or you find the gap when a bin runs dry.
- Consumption data. Issue logs, scans, vending draws, or an honest count on each visit. Any of these work, and none of them works if it only happens when someone remembers.
- Forward information. Mobilisation dates, phase changes, shutdown windows, a new shift pattern. Worth more than any amount of history, and the thing customers most often withhold.
- Item stability. If a line changes specification every few months, no replenishment rule keeps up. Fix the item list first.
This is why VMI and controlled-issue systems such as vending arrive together. The point is not the machine; it is a consumption record accurate enough for someone else to make decisions from.
VMI, consignment and imprest compared
Three terms, three different questions, routinely used as if they were interchangeable.
- VMI answers who decides the replenishment. The supplier does.
- Consignment answers who owns the stock until it is used. The supplier does, and it is invoiced on consumption.
- Imprest answers how the quantity is calculated. Top back up to a fixed agreed level, whoever owns it and whoever counts.
Combining all three gives the least admin and needs the most trust: the supplier is then deciding the quantity, owning the goods and raising the invoice.
Where VMI fails
The failures are predictable and mostly avoidable.
- No forward information. The supplier replenishes last month's pattern into next month's demand, then gets blamed for a shortage they could not see coming.
- One person holds it all. The arrangement lives in the head of a rep who knows the site. When they move, service falls off a cliff. Ask about holiday cover.
- Levels only go up. Where you own the stock the supplier carries no holding cost, so buffers creep. Review levels down as well as up.
- The wrong measure. Reporting that the visit took place proves nothing. Report stockouts by line, emergency orders raised outside the arrangement, and stock turns.
What to agree before you hand over replenishment
Keep it short, but write it down.
- The item list, levels and locations, with a review date and a named owner each side.
- The service measure and what happens when it is missed, in plain numbers.
- How new items are added, and who approves a substitution.
- The price mechanism and how long rates hold, so convenience does not quietly cost you a margin point a year.
- Exit terms: you should be able to ask for the item master, levels and twelve months of usage in a portable format at any time. If that is difficult, the arrangement holds you rather than serves you.
Common questions
What is the difference between VMI and consignment stock?
VMI is about who decides when to replenish. Consignment is about who owns the stock while it sits on your site. A supplier can manage replenishment of stock you own outright, and a supplier can own stock that you tell them when to replace. Many arrangements combine both, but they are separate decisions.
Does VMI mean losing control of what gets bought?
No, if the agreement is written properly. You approve the item list, the specification and the levels; the supplier decides only the timing and quantity within those limits. Adding a new line or substituting a product should need your sign-off. Where buyers lose control it is because nobody defined the boundary.
How do you measure whether VMI is working?
Track four numbers monthly: stockouts by line, emergency orders placed outside the arrangement, stock value held, and stock turns. If stockouts fall while stock value climbs, the supplier is holding more of your money on your shelf. Both have to move the right way before it is earning its place.
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