Safety stock calculator
How many buffer units you need so a deviation does not leave you out of stock.
≈ 4 minutes
Work out my safety stock
The reorder point for your inventory
The reorder point is the inventory level at which you have to order. Not earlier, because you tie up cash you do not need to; not later, because you run out while the order is in transit. It is built from the demand you will see during the lead time plus whatever buffer you want to hold in case something slips.
Every calculation runs in your browser. The figures you type are never sent to a server and are never stored.
Your results will appear here
Enter your daily demand, the lead time and your safety stock.
- Units you sell per day
- Days your supplier takes to deliver
- Safety stock you want to hold
Calculation results
Reorder point
—
When inventory drops to this level, it is time to reorder.
Demand during lead time—
Safety stock—
Inventory position—On hand plus ordered minus reserved
Reorder now?—
Days until reorder—
See the breakdown
| Daily demand | — |
| Lead time | — |
| Demand during lead time | — |
| Safety stock | — |
| Unrounded point | — |
| Reorder point | — |
Recommended next step
You know when to order. How much is usually decided by the supplier's minimum: check whether that quantity pays off before you commit the cash.
Evaluate the supplier MOQResults are estimates based on the information you enter. Fees, taxes and platform terms can change: always check the figure that matters to you against your invoice or the official platform. They do not replace your real invoices, your official accounts or professional tax, financial or legal advice.
What this tool works out
This inventory reorder point calculator tells you the stock level at which to place the order so new goods arrive before the old ones run out.
The reasoning is direct: if you sell twelve units a day and your supplier takes nine days, you will sell around a hundred and eight units while the order travels. You need at least that many on hand when you order, plus a buffer for the days you sell more than usual or the supplier runs late.
Oracle NetSuite defines the reorder point in exactly these terms — safety stock plus lead-time demand — and rounds up to the next whole unit, which is what this tool does too.
Inventory position, not shelf stock
Comparing the reorder point against what is physically in the warehouse is what causes duplicate orders. What you compare against is inventory position, which also counts what is in transit and deducts what is already committed.
With 200 units on the shelf, 50 arriving next week and 20 allocated to orders not yet shipped, your real position is 230, not 200. Ordering from the shelf figure alone means ordering the same thing twice.
It fails the other way round just as badly: 200 units with 180 allocated means a position of 20, and you are far closer to a stockout than it looks.
How the formula works
Two independent calculations that are then compared.
lead-time demand = daily demand x lead time in days
reorder point = round up(lead-time demand
+ safety stock)
inventory position = stock on hand
+ units already on order
- units allocated
order now = inventory position <= reorder point
days left = (position - reorder point) / daily demand
Rounding goes up because half a unit of protection protects against nothing: if the calculation asks for 142.5 units, the point is 143.
A worked example
A product selling 12.5 units a day, with a supplier taking 9 days and a safety stock of 30 units. The warehouse holds 200 units, 50 are already on order and in transit, and 20 are allocated to orders waiting to ship.
| Item | Value |
|---|---|
| Daily demand | 12.5 |
| Lead time in days | 9 |
| Demand during the lead time | 112.5 |
| Safety stock | 30 |
| Reorder point before rounding | 142.5 |
| Reorder point | 143 |
| Inventory position | 230 |
| Days until you must order | 7 |
The reorder point is 143 units. The real position is 230, not 200, so ordering is not due yet: there are almost 7 days of margin. Looking only at the shelf, the decision would have been the same here; with 180 units allocated instead of 20, it would not.
How to read the result
Days until reorder is the day-to-day operational figure. It tells you how long you have before ordering becomes due, assuming demand carries on as it has. It is the number you plan the week around.
When the verdict says order now, order now: every day of delay from there eats into your safety buffer. If the alert fires often and you still never run out, your safety stock is probably more generous than it needs to be and there is cash tied up unnecessarily.
The reorder point is not a figure you calculate once. It moves with demand and with your supplier's lead time, so it is worth recalculating whenever either shifts in a sustained way: a campaign, a peak season, or a change of supplier.
What this calculator does not do
It does not calculate how much to buy. The reorder point answers *when* to order; how much to order is a separate decision, driven by the supplier's minimum, volume discounts, and what holding the inventory costs you.
And it works from average figures. Demand of twelve units a day could be twelve every day or twenty some days and four others, and the stockout risk is very different. The reorder point does not absorb that variability: safety stock does, and it is calculated separately.
What to decide next
You know when to order. How much to order is almost always dictated by whatever the supplier forces you to buy at once, and it is worth checking that minimum does not tie up more cash than you can spare.
What this assumes
- Daily demand stays stable through the lead time
- The supplier meets the lead time you entered
- Safety stock already covers the variability you want covered
- Units on order will arrive before current inventory runs out
- The result is always rounded up to the next whole unit
What it does not cover
- How many units to order: that is a separate decision
- Calculating safety stock, which has its own tool
- Volume discounts or supplier minimum orders
- Seasonal demand or promotional spikes
- Partial stockouts caused by delays in transit
Frequently asked questions
Which daily demand do I enter?
The average units you sell per day over a representative period, usually the last four to eight weeks. If you have just run a campaign, that average is inflated: use a stretch without promotions or the calculation will have you ordering too much.
Why should I count units in transit?
Because they are already bought and they are coming. Ignore them and you will see the shelf below the reorder point and order the same thing again. Counting them is what turns physical stock into inventory position, which is what you actually compare.
What are allocated units?
Units committed to customer orders that have not left the warehouse yet. They are physically there but already spoken for, so they cannot serve new demand and have to come out of the position.
Does this calculator tell me how much to buy?
No, and the distinction matters. Here you learn when to order; how much depends on the supplier's minimum, volume discounts and what holding inventory costs you, which are separate decisions.
What if my supplier is often late?
Enter the lead time you actually observe, not the one you were promised, and raise safety stock to cover the variability in the delay. The reorder point works with whatever lead time you give it: give it an optimiztic one and you will run out occasionally.
Why is it rounded up?
Because units do not come in fractions and half a unit of protection protects nothing. If the calculation gives 142.5, the point is 143: rounding down would leave the buffer half a unit below what you decided to hold.
How often should I recalculate it?
Whenever demand or supplier lead time shifts in a sustained way: a change of season, a campaign that alters the sales rate, or a new supplier. Normal week-to-week variation does not call for a change.
What should I work out after this?
Whether the minimum order your supplier imposes makes sense. Knowing when to order helps little if the quantity you are forced to buy ties up more cash than you can spare.
Official sources
Oracle NetSuite — inventory optimization calculationshttps://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/article_0702045810.html
Related tools
Stockout cost calculator
What running out of stock really cost you, in lost contribution and extra spending.
≈ 4 minutes
Work out my stockout cost
MOQ profitability calculator
Whether the supplier's minimum order pays off once you have paid to hold it.
≈ 5 minutes
Evaluate the supplier MOQ