Every operator eventually asks a version of the same question: is there an easier way to know when to reorder than looking at the shelf and guessing? There is, and it is one line of arithmetic. What most versions of that line leave out is the part that matters for anything with a date on it.
This page covers the reorder point formula, how to pick the inputs so it does not quietly fail, and the shelf-life cap that has to sit on top of it for food and drink.
What is the reorder point formula?
Reorder point equals average daily demand multiplied by lead time in days, plus safety stock. It answers one question: at what stock level do you place the order so that replenishment lands before you run out? Cross that level and you order, regardless of what the calendar says.
| Input | Value | Where it comes from |
|---|---|---|
| Average daily demand | 40 units | Recent sales, not last year's |
| Lead time | 14 days | Order placed to stock available, realistic worst case |
| Demand during lead time | 560 units | 40 × 14 |
| Safety stock | 180 units | Buffer for demand and lead-time variability |
| Reorder point | 740 units | 560 + 180 — order when stock hits this |
Two inputs decide whether this works, and both are usually taken too optimistically. Lead time should be the realistic worst case rather than the quoted one: the number that matters is order placed to stock actually available to pick, which includes the supplier's own slippage, transit, and the day it sat on your dock before anyone put it away. And demand should come from recent weeks rather than an annual average, because an annual average is wrong in both directions for anything seasonal.
If you do not know your lead time, you can measure it from what you already have. Take the last five or six purchase orders for that supplier and, for each one, count the days from placing the order to the stock being on the shelf and pickable. Not to the invoice, and not to the delivery arriving on the dock — to the moment somebody could actually pick it. Those two extra steps are where most of the hidden days live.
Then take the worst of those numbers rather than the average. An average lead time leaves you short roughly half the time by construction, which is the opposite of what the buffer is for. If you have no order history at all, ask the supplier for their quoted time, add a week, and replace the estimate with your own measurement after three orders. A guess you correct in two months beats a formula you never start.
What is the shelf-life cap?
A ceiling the standard formula does not have: never carry more than the selling window can absorb before the date runs out. If the reorder point plus the order quantity exceeds what you can sell inside the remaining shelf life, the formula is telling you to buy a write-off in advance.
This is the point where generic reorder-point advice stops being safe for food and drink. The classic formula optimises against one failure — running out — and treats holding stock as merely expensive. For dated goods there is a second failure that is not merely expensive: stock that ages past the point where anyone will take it. Buffering harder makes the first failure less likely and the second more likely, and past a certain point you are trading a stockout you might have survived for a write-off you certainly will not.
The practical form is a check rather than a new formula. Work out the reorder point, then ask how many days of cover the resulting position represents, and compare that against the remaining shelf life at the moment the delivery lands. Where cover exceeds the window, the answer is a smaller, more frequent order, not a bigger buffer — which is the same ceiling that governs how much buffer the selling window absorbs.
When should you recalculate?
When demand shifts, when a supplier's lead time changes, and after any stockout or write-off. Not on a schedule. If demand doubles in March and you next recalculate in June, the number was wrong for three months. The calendar will not tell you that. The stockout will.
The events worth wiring an actual review to are narrow: a sustained change in weekly sales, a supplier changing terms or missing a delivery window twice, a new channel coming online, and any SKU that ran out. That last one is the most useful and the most often skipped — a stockout is direct evidence that either the demand figure or the lead-time figure was wrong, and it is worth finding out which before setting the number back to where it was.
Once the number is right, the work should disappear. The reorder point exists so nobody has to make the decision daily; if somebody is still checking shelves each morning, the number is not doing its job. Reordering is one of the four places cash leaks in a CPG operation, and it is the one that automates most cleanly.
What should you do next?
One pass per SKU, then let it watch itself.
Gather the inputs
- Take average daily demand from recent weeks, not the year.
- Measure lead time as order placed to stock pickable.
- Use the worst case you have actually seen, not the quote.
Apply the cap
- Convert the resulting position into days of cover.
- Compare against remaining shelf life on arrival.
- Where cover exceeds the window, order smaller and more often.
Keep it honest
- Recalculate after any stockout or write-off.
- Review when a supplier misses a window twice.
Frequently asked questions
How do I know when to reorder without checking every day?
Set the reorder point once per SKU and let the number watch itself. The point of calculating it is that you stop making the decision daily: stock crossing the line is the signal, and the only recurring work is recalculating when demand or lead time actually shifts.
What if my lead time keeps changing?
Use a realistic worst case rather than an average. An average lead time leaves you short roughly half the time by construction, which is the opposite of what a buffer is for. If the spread is wide, that variability is the thing to fix with the supplier, not to absorb with stock.
Is the reorder point the same as safety stock?
No. Safety stock is the buffer. The reorder point is the buffer plus whatever you expect to sell while the replenishment is in transit. Reordering at your safety stock level means you start eating the buffer the moment you place the order.