Harpy Glossary

Inventory Replenishment

Amazon & D2C glossary · Harpy Media

Inventory replenishment is the decision logic for keeping stock flowing: when to reorder, how much, and where it should live — timed so products stay available without capital drowning in warehouses. It’s demand forecasting converted into purchase orders and shipping schedules.

What is Inventory Replenishment?

Replenishment is where the two expensive mistakes live: order late and a stockout interrupts rank and revenue (the recoveries take months); order early or heavy and capital parks in storage, aging toward surcharges. Neither failure announces itself politely — both surface as money moving the wrong way — and both are avoidable with the same instrument: a replenishment model the business actually runs.

The components of sound replenishment

Four inputs, each measurable. Velocity: how fast each SKU actually sells (recent trend, cleaned of promo spikes). Lead time: true door-to-sellable time from each source — supplier production plus freight plus inbound plus receiving; the number optimism consistently understates. Variability: both demand variability (how noisy the SKU’s sales are) and supply variability (how reliable the source is) — these two determine the safety stock that keeps a good quarter from becoming a stockout. And economics: reorder quantity balancing freight efficiency (bigger shipments, cheaper per unit) against carrying cost and cash (bigger shipments, slower capital). The output is a reorder point and an order quantity per SKU — refreshed monthly, not set annually.

Running replenishment as a rhythm (not a rescue)

The operating cadence that works: a weekly review of SKU-level cover (days of stock against projected velocity), orders triggered by the model’s reorder points rather than by human alarm, and exception handling for the events models can’t see (a promotion scheduled, a competitor’s stockout, a supplier hiccup — each adjusts the inputs deliberately). The financial lens that keeps it honest: replenishment planning IS cash-flow planning — every PO is a cash commitment dated by its lead time — so the model should live beside the cash forecast, not in a separate spreadsheet world. The mature end state for scaled sellers: replenishment tooling (Amazon’s own guidance, third-party planners, or an ERP) automating the arithmetic, with humans handling the exceptions and the economics — because the goal isn’t to eliminate judgement; it’s to stop spending judgement on arithmetic.

Reorder point = (average daily velocity × lead time days) + safety stock · Order quantity = balancing freight efficiency against carrying cost and cashPer SKU, refreshed monthly — and hooked into the cash forecast, because every PO is dated money.

In practice

A seller rebuilds replenishment for their top 20 SKUs with honest lead times (12–18 days longer than the old assumptions, once receiving was counted) and variability-based safety stock. The first month prevents two near-certain stockouts the old model would have caused (they were ordering against supplier promises, not door-to-sellable reality), and holding cost actually FALLS — because the safety stock that was blanket-sized everywhere got right-sized per SKU. Better availability and less capital, from the same demand data, correctly arithmetic’d.

⚠️ Watch out. A seller replenishes by gut and recency — topping up whatever ran low, splitting a bulk order in a panic, and judging “enough stock?” by looking at shelves rather than cover math against lead times. The model-free style books its failures as bad luck: the stockout was “sudden,” the overstock was “unexpected” — though both were scheduled by arithmetic nobody ran.

💡 Harpy tip. For every SKU, write its lead time in door-to-sellable days and its reorder point next to current cover. The gap between “days left” and “days to restock” is the whole conversation.

How Harpy Media helps

Replenishment modelling — honest lead times, variability-based buffers, and order-point discipline — is a standing workstream on our accounts, tied directly into cash planning.