Reorder points vs. safety stock: stop stockouts without freezing your cash

Two numbers decide whether you stock out or tie up cash: safety stock and the reorder point. They sound interchangeable. They are not. Confusing them is how you end up either out of your best seller or sitting on six months of a SKU that turns twice a year.

Safety stock: your buffer against surprise

Safety stock is the extra inventory you hold to absorb the things you cannot predict: a demand spike, a supplier who ships late, a customs delay. It is insurance, and like all insurance it has a price, the cash locked in those extra units.

A serviceable starting formula:

Safety stock = (max daily sales × max lead time) − (avg daily sales × avg lead time)

This sizes the buffer to your variability, not just your average. A SKU with steady sales and a reliable supplier needs almost no safety stock. A volatile SKU with a flaky supplier needs a lot.

Reorder point: the line that triggers the order

The reorder point is the stock level at which you place a new order. It has to cover expected demand during the lead time, plus your safety stock:

Reorder point = (avg daily sales × avg lead time) + safety stock

Hit that number, place the order. The goal is for the new shipment to arrive just as you are eating into the safety buffer, not weeks early (cash frozen) and not after you have already stocked out (sales lost).

A worked example

Say you sell a hero SKU with these numbers:

• Average sales: 20 units/day; on a spike, up to 32 units/day
• Average lead time: 14 days; worst case, 21 days

Safety stock = (32 × 21) − (20 × 14) = 672 − 280 = 392 units.

Reorder point = (20 × 14) + 392 = 280 + 392 = 672 units.

So when this SKU drops to 672 units on hand, you order, and you keep roughly 392 units as your cushion against a bad week or a late container.

The cash tradeoff nobody likes to say out loud

Every unit of safety stock is a dollar you cannot spend on a faster mover, ads, or a new product. The right buffer is not the one that guarantees you never stock out, that is infinitely expensive. It is the one where the cost of one more unit of buffer is no longer worth the stockout risk it removes.

That is why a service level of 95 to 98 percent is usually the sweet spot for a healthy SKU, and why your slow, low-margin items deserve a thinner buffer than your hero products.

Common mistakes

• One buffer for every SKU. Variability differs wildly across your catalog; so should your safety stock.
• Ignoring lead-time variability. A supplier whose ship date swings by a week is riskier than a slow but punctual one.
• Setting it once. Demand and lead times drift. Reorder points are a living number, not a one-time setup.

Let the tool do the arithmetic

InventoryIQ computes safety stock and reorder points per SKU from your real sales and lead-time history, then ranks the resulting reorders by ROI so you fund the ones that pay back first. Start a free trial and see your own numbers.