How to Manage Inventory on Amazon (With the Reorder Math)

What 'managing inventory' on Amazon actually means

Managing inventory on Amazon means five ongoing jobs, not one: forecasting how much you'll sell, deciding when to reorder before you run out, staying inside Amazon's storage and performance rules, checking what Amazon actually received against what you shipped, and recovering money on lost, damaged or misclassified units. Do all five and stockouts and surprise fees mostly stop happening. Skip one and it shows up later as a number you don't like — an IPI score, a storage bill, a denied reimbursement.

• Demand forecasting — projecting sales forward from history, adjusted for seasonality and anything marketing is about to do
• Reorder timing — placing the next purchase order early enough that stock lands before you run out
• Performance compliance — keeping your IPI score and storage usage inside Amazon's limits
• Receiving reconciliation — checking what Amazon says arrived against what you actually shipped
• Reimbursement recovery — claiming back lost, damaged, or overcharged units

A single-SKU seller can run this in a spreadsheet. A cookware brand like HexClad shipping into wholesale and Amazon at once, or a seasonal business like Epic Gardening with spring demand spikes, usually can't — the forecasting inputs and the timing windows are different for every SKU and every channel.

The reorder point math, worked through

The core formula behind reorder timing is simple: reorder point = (average daily units sold × total lead time in days) + safety stock. Total lead time means the whole gap from placing the purchase order to units being live and sellable on Amazon — production time, freight, and Amazon's own receiving lag, not just what the factory quotes.

Say a SKU sells 40 units a day. Production plus freight plus Amazon receiving runs 45 days end to end. Add 10 days of safety stock for demand variability. Reorder point = (40 × 45) + (40 × 10) = 2,200 units. That's the inventory level that should trigger the next PO — not 'when I remember to check,' and not Seller Central's default restock alert, which is usually built off a trailing 30, 60 or 90-day sales window and has no idea a campaign is about to scale demand.

Full Circle has managed more than $500M in revenue across 100+ brands, and the most common cause we see behind a mid-campaign stockout is exactly that mismatch: the reorder point calculated from trailing sales the week before a launch, not the week after it. The math wasn't wrong. The timing of the input was.

IPI score and storage limits — what they actually punish

Amazon's Inventory Performance Index rolls excess inventory, stranded inventory, in-stock rate and sell-through into one score, visible in Seller Central under Inventory Performance. Fall below the threshold Amazon sets for your account — and that threshold moves, so check it rather than remember it — and you can hit storage limits or extra long-term storage fees on top of the usual monthly rate.

The mistake most sellers make here is treating the score itself as the problem. It isn't — it's a symptom of one of four inputs. Chasing the number without fixing the input, usually excess stock sitting past 90, 180 or 365 days, tends to produce a score that recovers for a quarter and then drops again.

When the answer is bad news: wrong forecast, denied claim, fix that didn't work

• The forecast was wrong — check whether it used a trailing window that predates a promotion, price change or listing edit; rebuild it with the marketing calendar included, not sales history alone.
• The reorder was on time but stock still ran out — the gap is usually freight, not the PO. Measure lead time from PO date to sellable, not from the factory's quoted ship date.
• The IPI score didn't recover after a fix — you likely fixed the surface stock level, not the SKU driving it; pull the excess-inventory report by ASIN, not the account total.
• A reimbursement claim was denied — check the shipment reconciliation report against the original ASN before resubmitting; most denials are a documentation gap, not a policy one.
• Aged stock triggered a surcharge — run the removal-versus-liquidation math on that specific SKU before defaulting to either; removal fees and liquidation recovery rates both vary enough that 'just remove it' is often the wrong default.

The mistakes worth naming, including the ones we've made

Most inventory problems on Amazon trace back to one of three habits, and we've made at least one of them ourselves.

The first is setting reorder points off a trailing sales window right as a campaign is about to scale — we've mistimed a reorder against a launch we were running the ads for, and learned to pull the marketing calendar into the lead-time math every time now, not just when it seems relevant.

The second is defaulting to removal for aged inventory without running the liquidation numbers first — removal has its own fee, liquidation recovers some value, and which one wins depends on the SKU, not on a blanket rule.

The third is fixing the IPI score instead of the input causing it — a score that improves without the underlying excess stock actually moving is a score that drops again next quarter.

Where each tool actually helps

Not every inventory problem needs the same fix, and it's worth being precise about which tool does what.

• A 3PL physically stores and ships product — useful for overflow, prep, or multichannel fulfillment outside FBA. It doesn't decide what or when to reorder.
• An ERP or multichannel inventory system runs the whole business across every sales channel, not just Amazon. If you're managing inventory across retail, DTC and marketplaces at real scale, that's the right layer — an Amazon-specific tool feeds it, never replaces it.
• A research suite is built to find products worth selling, not to work a fee dispute or a reimbursement claim after the fact. Different job entirely.
• If the actual leak is in the ad account — wasted spend, bad targeting, a campaign scaling faster than inventory can support — that's a Dr. PPC problem, not an inventory one, and worth separating out before spending time on the warehouse side.

Where Dr. Stock fits

Dr. Stock is Amazon inventory, fees and supply chain run as a managed product by Fable 5, from Full Circle — the same team behind $500M+ in managed revenue across 100+ brands. It doesn't store or ship anything (that's a 3PL's job) and it doesn't replace an ERP if you're running multichannel at real scale. What it does: catches FBA fee misclassifications, chases lost-unit reimbursements, calls the removal-versus-liquidation decision on aged stock, and sets reorder timing that accounts for what marketing is about to do to demand — with purchasing decisions always going to a human, whichever autonomy level a client picks. Orbit, included at no extra cost, is the dashboard behind that: inventory, finance, ASIN profitability, and the BSR, buy box, price and fee trackers. There's no published price — it's a demo and a 30-day free trial, priced on the call.