--- title: "What Is Vendor Managed Inventory (VMI)?" url: https://www.uncap.com/glossary/vendor-managed-inventory author: "Denis Dyli" published: 2026-10-14 updated: 2026-10-14 summary: "Vendor managed inventory (VMI) is an arrangement in which the supplier, not the buyer, monitors and maintains specified inventory levels for selected items at designated stocking points. The buyer shares inventory and sales data, and the supplier decides order size and timing. In traditional inventory management, the buyer makes those decisions itself." --- # What Is Vendor Managed Inventory (VMI)? > Vendor managed inventory (VMI) is an arrangement in which the supplier, not the buyer, monitors and maintains specified inventory levels for selected items at designated stocking points. The buyer shares inventory and sales data, and the supplier decides order size and timing. In traditional inventory management, the buyer makes those decisions itself. **Vendor managed inventory (VMI)**: Vendor managed inventory (VMI) is an arrangement in which the supplier, not the buyer, monitors and maintains specified inventory levels for selected items at designated stocking points. The buyer shares inventory and sales data, and the supplier decides order size and timing. In traditional inventory management, the buyer makes those decisions itself. ## How it works Under VMI the supplier becomes the decision maker on order size and carries the ordering cost, while the customer usually takes ownership of the stock and pays its own holding cost. A 2008 article notes that VMI has no standard definition and that usage of the term varies significantly between companies. A US federal acquisition clause, GSAM 552.238-92, names the gains on both sides: VMI enables the contractor to plan production and shipping more efficiently, and stocking points benefit from reduced inventory but steady stock levels. What makes it work is shared demand data. The information a supplier may see includes sales data, stock withdrawals, production schedules, inventory levels, goods in transit, back orders, incoming orders and returns. Three choices shape a VMI program: - Where the stock sits. At both the customer's and the supplier's premises, at the customer's central warehouse or a third party's warehouse, or directly at the customer's site, such as an on-site warehouse, production line or shop floor. - Who owns it, and when the invoice goes out. The vendor can own the stock at the customer's site and invoice when items are issued from it. The customer can own it but pay only when items are issued. Or, as in traditional ordering, the customer owns the stock on delivery and is invoiced on shipment. - Which model. In "consigned VMI" the supplier keeps ownership, which is consignment inventory. In "dynamic VMI" the buffer stays with the supplier, so it can be shared among several distributors. ## VMI in EDI X12 publishes transaction sets whose documented uses match the steps of a VMI cycle. The 852 Product Activity Data advises a trading partner of inventory, sales and other product activity, so that partner can plan and ship, or propose replenishment quantities. The [846 Inventory Inquiry/Advice](/glossary/edi-846) lets one location supply another with inventory information. The diagram below is an illustration: it lines up each set's documented use in the order a supplier-run replenishment would follow. **How X12 documents can carry a VMI replenishment** ### 1. 852, Product activity data The distributor, warehouse or retailer advises its trading partner of inventory, sales and other product activity. ### 2. Plan, Replenishment quantities The data enables the trading partner to plan and ship, or to propose replenishment quantities. ### 3. 855, Vendor generated order The 855 can notify the buyer that the vendor has or will ship merchandise as prearranged in their partnership. ### 4. 856, Ship notice/manifest The 856 lists the contents of the shipment, with order, product, packaging and carrier information. ## Example Illustrative numbers only. A fastener maker runs VMI for an industrial distributor. They agree the maker will keep each SKU at the distributor's warehouse between 400 and 1,200 units, and the distributor sends product activity data every Monday. This week's data for one SKU shows 1,050 units at the start of the week, 690 units sold and nothing received, so 1,050 - 690 = 360 units on hand. That is below the agreed 400, so the maker plans a refill to the top of the range: 1,200 - 360 = 840 units. It notifies the distributor of the vendor generated order and ships. The distributor never wrote a purchase order, and its shelf is back at 1,200. ## On Shopify If the buyer runs on Shopify, its stock data is already there. Shopify tracks inventory separately at each location, and a location is any physical place where you sell products, fulfill orders or stock inventory. Through the GraphQL Admin API, an integration can query each location's quantities by state, including available, on_hand, committed and incoming: the inventory level and in-transit figures a VMI supplier works from. If the supplier sells on Shopify, Shopify documents a route for orders that do not come through checkout: the orderCreate mutation in the GraphQL Admin API, meant for orders imported from an external system or created for wholesale customers. ## How Uncap helps Uncap's [Shopify ERP sync design spec](/post/shopify-erp-inventory-sync-design) starts with an ownership map: for every field that crosses the boundary, name the single system allowed to write it. Inventory quantities: the ERP writes, Shopify displays. ## Related terms - EDI 846 - EDI 855 - EDI 856 - Consignment inventory - Reorder point - Safety stock ## Sources - 552.238-92 Vendor Managed Inventory (VMI) Program, General Services Acquisition Manual - X12 Transaction Sets - Vendor-managed inventory, Wikipedia ## Frequently asked questions ### What does VMI stand for in supply chain? VMI stands for vendor managed inventory: the supplier monitors and maintains specified stock levels for its customer and decides when and how much to replenish, using the inventory and sales data the customer shares. ### How does vendor managed inventory (VMI) work? The customer shares data such as sales, inventory levels and back orders. The supplier uses it to set order size and timing, ships, and in EDI can send an 855 as notice of a vendor generated order. Contract terms decide who owns the stock and when it is invoiced.