A stockout costs more than the missed sales
The obvious cost of going out of stock is the orders you can't fulfill. The hidden — and usually larger — cost is rank. Amazon's ranking rewards velocity and conversion; when a listing goes dark it stops earning those signals and slips down the page. So even after you restock, you don't return to your old sales rate immediately — there's a recovery ramp while you rebuild position. Budget both: the sales lost during the gap, and the slower weeks that follow.
Overstock is a silent tax
The opposite mistake feels safer but isn't free. Every excess unit pays monthly storage(steeper in Q4) and, once it's sat long enough, aged-inventory surcharges. The bigger cost is invisible on any fee report: the cash those units tie up, which you could have spent on your next order or a new product. Overstock compounds quietly against your growth.
The reorder point
You don't reorder when you hit zero — you reorder when the stock you have left will just cover the time it takes new stock to arrive. That threshold is your reorder point:
reorder point = daily velocity × lead-time days + safety stock
If you sell 20 units a day and your supplier plus freight take 45 days, you burn 900 units before a new shipment lands — so you reorder while you still have those 900 (plus a buffer) on hand, not when the shelf is bare.
Safety stock: buying insurance
The reorder point assumes average demand and an on-time supplier. Safety stock is the buffer for when neither holds — a sales spike, or freight stuck at port. A bigger buffer means fewer stockouts but more cash and storage committed, so size it to your reality: steady demand and a reliable factory need little; spiky demand or unpredictable shipping need more.
Watch the cash, not just the units
Behind every restock decision is cash. The cash conversion cycle is how many days each dollar stays locked in inventory before Amazon pays it back to you. Order too much too early and you strangle the cash you need to grow; order tight and you free it up. Restock timing and cash flow are the same decision looked at two ways — this is where the true-profit math from the profit guide meets operations.
Plan from real velocity
All of this runs on two inputs you already have: how fast each SKU actually sells, and how long your supply chain takes. A restock planner reads your real sales velocity, applies your lead time and a safety buffer, and tells you the reorder date and quantity per SKU — before a stockout or an overstock can happen.
FAQ
What does a stockout actually cost?+
More than the sales you miss while you're dark. Going out of stock also drops your organic rank — the listing loses the velocity and conversion signals that earned its position — so when stock returns you don't snap back to your old volume; there's a recovery ramp. The true cost is the lost sales during the gap plus the slower period afterward.
What is a reorder point?+
The stock level at which you place your next order — not when you hit zero, but when what's left will just carry you through the supplier lead time. The basic formula is reorder point = daily sales velocity × lead-time days + safety stock. Hit that level and it's time to reorder.
How much safety stock should I hold?+
Enough to absorb the two things that go wrong: demand spiking above your average, and the supplier or freight running late. More buffer means fewer stockouts but more cash and storage tied up, so the right size scales with how variable your demand and lead times actually are — steady product and reliable supplier, thin buffer; spiky demand or flaky shipping, thicker.
Why is overstock a problem if it eventually sells?+
Because it costs you the whole time it sits. Excess units pay monthly storage (higher in Q4) and aged-inventory surcharges, and — the bigger cost — they lock up cash you can't put toward your next order or a new product. Overstock is a quiet, compounding tax on growth.