When should you reorder? The beginner mistakes of restocking
There are two expensive mistakes in selling on Amazon, and most beginners believe they are opposites.
One is the stockout. Inventory runs out, the ads stop, the listing slides down in search, and when you have stock again you do not continue where you left off. It takes weeks to climb back.
The other is trapped capital. You ordered too much, it sits in the warehouse, you pay storage on it, and your money cannot work on another product.
These two are not opposites. They are two ends of the same gap: you do not know how fast your product sells, and how long it takes to refill.
The arithmetic behind it
You need three numbers, nothing more.
1. Daily velocity. How many units leave per day. Do not use yesterday: use at least a 30-day average, because a single good day distorts the picture.
2. Lead time. Counted from the moment you place the order: how many days until the product is sellable in Amazon's warehouse. This is not the manufacturing time. It includes shipping, customs, and the time Amazon takes to receive and activate the inbound shipment. That last part is what beginners leave out, and it alone can be one or two weeks in peak season.
3. Safety stock. The buffer that absorbs the season, a sudden ramp-up and a shipping delay.
Reorder point = daily velocity x lead time + safety stockIf daily velocity is 8 units, lead time is 45 days and you keep two weeks of buffer:
8 x 45 = 360 units, plus 8 x 14 = 112 units of buffer
Reorder point: 472 unitsSo when your stock drops to 472 units, that is when you order — not when it is about to run out. At that moment most beginners still see the stock as plentiful, and that is the trap.
The four mistakes that break it
Gut feeling. "There's still plenty." "Plenty" is not a unit count, and it has no relation to your lead time.
One number for the whole portfolio. A slow-moving, expensive product has a completely different reorder point than a fast-moving, cheap one. A shared rule fails on both — in opposite directions.
Ignoring the season. Before the fourth quarter, velocity jumps and supplier lead times stretch at exactly the same time. The two effects reinforce each other; they do not cancel out.
Treating ads and inventory separately. If your advertising accelerates sales, your velocity rises — so your reorder point rises too. Whoever scales a campaign without knowing the stock will sell themselves out of inventory.
How SellHelm helps here
The inventory module keeps this same arithmetic continuously up to date. In one view you see stock levels and sales velocity, with the reorder guidance next to them, so the decision is a reading rather than a guess.
What is worth more: it is the same surface where your profit data and your advertising data live. Because the question is almost never "should I reorder" — it is "is this product still worth tying money into". You can only answer that when the margin sits next to the velocity.
SellHelm's seller tools are free with every account, and inventory management is one of them.
Where to start
1. Write down the daily velocity of your top five products from a 30-day average. 2. Ask your supplier for the honest lead time, and add two weeks for Amazon-side receiving. 3. Compute the reorder point for all five with the formula above. 4. Put them somewhere you actually look. Good inventory management does not come from a clever formula — it comes from someone actually checking.
These four steps take one morning. The stockout they prevent would cost weeks.
Related: What do you actually earn on an Amazon product?