Reorder point calculator
“When should I reorder, and when is stock genuinely low?”
Two answers out of the same three numbers. How fast the product moves and how long your supplier takes decide when to place the next order — and the same figures decide the stock level at which “only a few left” is a fact rather than a nudge.
The product
A recent average, not a peak week. Shopify reports this under sales by product.
Order placed to stock sellable — including the days it sits in receiving.
How much week-to-week variation there is. Spikier demand needs a deeper buffer.
The share of restock cycles you expect to get through without running out.
Reorder point
136 units
120 units sell while you wait out the 21 days lead time, plus 15 of safety stock for a bad run at 95% service.
17 days
At 5.7 units a day.
15 units
35% demand variation.
95 units
41 below the trigger.
Order now
You are at 95 units against a reorder point of 136. At the current rate the shelf is empty in 17 days, and a fresh order takes 21 days to land — so you are already looking at 4 days out of stock unless the supplier can move faster.
Badge thresholds
The stock levels at which a scarcity badge is describing something real. Below these numbers the product genuinely runs out before it can be restocked — above them, the badge is decoration, and shoppers work that out faster than merchants expect.
40 units
A week of cover left.
12 units
Two days of cover left.
How the maths works
The reorder point is lead time demand plus safety stock. Lead time demand is simply your daily sales rate multiplied by the number of days you wait for stock — what walks out of the door while the pallet is in transit.
Safety stock covers the weeks that run hotter than average. It is the service level’s z-score multiplied by the standard deviation of daily demand, multiplied by the square root of the lead time. The square root is the part worth understanding: a lead time twice as long does not need a buffer twice as deep, because good weeks and bad weeks partly cancel out over a longer wait.
Merchants do not know their standard deviation, so the demand pattern selector asks the question in terms you can answer and turns it into a coefficient of variation — 15% for steady sellers, 35% for ordinary variation, 60% for products that move in promo and drop-driven bursts.
The service level is the share of restock cycles you expect to get through without running out. 95% is the usual choice. Pushing it to 99% is a real decision with real cash behind it, because the buffer grows faster than the confidence does.
Why the badge threshold belongs on this page
A scarcity badge is a claim about the future: buy now, because this will be gone. Whether that claim is true depends on exactly the numbers a reorder point already uses — how fast the product sells and how long a restock takes.
So the honest threshold is expressed in cover, not units. A week of cover left is a reasonable line for a low-stock badge and about two days for an almost-gone one. Both scale with velocity, which is why a single number applied across a catalogue always misbehaves: it will fire permanently on your slow movers and never on the products where the urgency is real.
There is one combination worth watching for. If a week of cover is more stock than your reorder point, the badge fires on inventory you would still be restocking through — the product is not actually scarce, it is just being replenished. The calculator flags that case rather than handing you the number anyway.
Questions
- What is a reorder point?
- The stock level at which you place your next purchase order. It is what sells during the supplier's lead time plus a safety buffer for the weeks that run hot. Order at that level and new stock arrives about as the old stock runs out.
- How do you calculate a reorder point?
- Multiply your average daily sales by the lead time in days, then add safety stock. Safety stock is a service-level multiplier times the standard deviation of daily demand times the square root of the lead time — variation accumulates over the wait, so the buffer grows with the root of the lead time rather than in step with it.
- What stock level should a low stock badge use?
- A level the product will actually sell through. If you show a low-stock badge at a number you can comfortably restock past, the badge appears on healthy inventory and shoppers learn to ignore it. Roughly a week of cover is a defensible threshold for a low-stock badge and about two days for an almost-gone one — both scale with how fast the product moves, which is why one fixed number across a catalogue never works.
- Why does the same threshold not work for every product?
- Because a threshold in units means nothing without a rate. Five units left is a fortnight of cover on a product that sells two a week, and half a day on one that sells sixty. A badge rule set to a flat number will fire constantly on slow movers and almost never on the products where urgency is real.
- Is a low stock badge worth showing at all?
- When it is true, yes — it is genuinely useful information, and it prevents the shopper who would have come back next week from missing out. When it is decoration it does more harm than good, because it trains people to discount everything else your store tells them. The thresholds on this page exist to keep it on the honest side of that line.
The app that does this for you
Quarter Product Badges
Rule-based product badges
Sale, new arrival, low stock, bestseller — badges that follow rules instead of manual tagging, delivered by a storefront script small enough to forget about.
Rule engine / ~2 KB script / Theme app extension
In development
Join the waitlistNo install button yet — this opens an email. We will write once, when it ships.