Use this free reorder point calculator to figure out the exact stock level at which you should place your next supplier PO. Built for Shopify merchants in supplements, beauty, CBD, pet, and other high-AOV categories where stockouts hurt more than holding cost. Enter daily sales, lead time, and service level. The tool calculates safety stock, stress tests against demand spikes, and shows your monthly stockout cost risk in dollars.

How to use this reorder point calculator

1. Enter your average daily sales

Pull your last 30 to 90 days of daily unit sales from Shopify analytics. If the SKU is seasonal, use a window that matches your current season, not a trailing 12-month average. Supplements and pet brands usually see 5 to 10 percent week-over-week variance; apparel and beauty can swing 20 to 40 percent around launches and promos.

2. Enter your supplier lead time

Count from the moment you place the PO to the moment stock lands in your warehouse and is ready to ship. Include supplier production time, freight transit, customs clearance, and receiving. Most US Shopify supplement brands run 18 to 24 days. Beauty runs 14 to 28. Apparel stretches to 45 to 75 when manufactured overseas.

3. Pick your service level target

95 percent is the default. It means you will stock out roughly 1 in 20 reorder cycles. Supplements, CBD, and subscription products often justify 97.5 or 99 percent because a single stockout breaks subscribe-and-save LTV. Apparel and food brands frequently run at 90 to 95 percent because holding cost matters more and stockouts are easier to recover from.

4. Optional: enter daily sales variability

If you leave the std dev field blank, the calculator estimates 30 percent of your average daily sales, which is typical for Shopify stores. For a cleaner number, export daily unit sales into a spreadsheet and run STDEV.P. High-launch brands often see std dev closer to 50 to 60 percent of average.

5. Read the reorder point and stress test

The headline number is the stock level at which you should place your next supplier PO. The ladder below shows how that number moves if demand rises 10 percent, if lead time stretches 20 percent, or if both hit at once. Most stockouts happen on the last row, not the first.

What is a reorder point?

A reorder point (ROP) is the inventory level that triggers your next purchase order. When on-hand stock drops to the ROP, you place a PO large enough to arrive before you run out. It is the bridge between demand planning (how much you sell) and supply planning (how long replenishment takes).

Think of it as a buffer with two jobs. The first job is covering normal demand during the lead time while your PO is in transit. The second job is covering the variability of that demand. Shopify stores rarely sell the exact same number of units every day. A viral TikTok, a B2B bulk order, or a weekend promo can spike sales by 50 percent. A reorder point set to average demand alone will stock out half the time.

The APICS / ASCM Supply Chain Operations Reference Model defines ROP using two inputs: expected demand during lead time, plus a safety stock buffer sized to your chosen service level. Shopify's own inventory documentation covers the basics of tracking on-hand stock but does not give you a formula. The calculator above uses the standard industry formula, grounded in the normal distribution of daily demand.

Reorder point formula explained

The reorder point formula:

Reorder Point = (Avg Daily Sales x Lead Time) + Safety Stock

Safety Stock = Z x sqrt(Lead Time) x Std Dev of Daily Sales

Z-score by service level:

• 90% service level -> Z = 1.28
• 95% service level -> Z = 1.65
• 97.5% service level -> Z = 1.96
• 99% service level -> Z = 2.33
• 99.9% service level -> Z = 3.09

Worked example: supplement brand, 40 units/day, 21-day lead time, std dev of 12 units/day, 95% service level.

• Demand during lead time = 40 x 21 = 840 units
• Safety stock = 1.65 x sqrt(21) x 12 = 91 units
• Reorder point = 840 + 91 = 931 units

When stock drops to 931 units, place the PO. By the time the shipment arrives 21 days later, you will have sold about 840 units and have 91 units of buffer left. If demand spiked 10 percent or the shipment delayed by 4 days, you still would not stock out.

Most stockouts come from one of three things: the brand does not have a formal reorder point and reorders when it "feels low", the reorder point ignores variability and sets safety stock to a round number, or the brand never re-runs the calculation when daily sales grow. A brand selling 100 units/day today but still reordering on the 40/day math will hit a shelf-empty moment within one cycle.

Example calculations

Three realistic Shopify merchant scenarios:

The supplement example uses a higher service level because subscribe-and-save customers are at risk of churning on a single missed refill. Published inventory-planning research like Nahmias's Production and Operations Analysis shows the optimal service level climbs when per-unit stockout cost is high relative to per-unit holding cost, which is exactly the supplements and CBD profile. The pet brand runs 95 percent because most customers buy on a predictable cadence and a 1-day delay rarely breaks the relationship. The beauty brand sits in the middle.

Note the safety-stock share of each reorder point. The supplement brand carries 11 percent of its ROP as safety stock; the beauty brand 9 percent; the pet brand 13 percent. Safety stock looks small in absolute terms but drives most of the stockout prevention. Cutting it to save holding cost is the first place brands get burned.

Why reorder points matter for Shopify merchants

Most Shopify founders manage inventory on gut feel until the first big stockout. Gut feel works for the first 10 SKUs. At 50 SKUs across 3 suppliers with different lead times, gut feel starts producing a stockout every few months, then every few weeks. The cost shows up in three places: lost sales during the stockout window, permanent customer loss from subscribers who churn, and a tax on your support team.

That last one is the invisible cost. Stockouts drive 8 to 12 percent of inbound support calls. "Is this back in stock yet?" "Why did my subscription skip?" "Can you send me the old version?" Those calls are expensive per minute and demoralizing for agents because the answer is almost always "we do not know yet". Our breakdown of Shopify customer service costs shows how these calls compound when multiple SKUs go out at once.

A properly set reorder point prevents most of those calls. A phone-based restock alert system recovers the customers you do lose. This is the Ringly angle, and it is built into the calculator above. When you tick the "phone support as in-stock alert channel" checkbox, the stockout risk drops by about 45 percent because AI phone agents answer these calls, take the customer's email, and route them to a pre-order or substitute instead of letting them bounce.

The math on phone support has changed in the last 18 months. Human phone agents cost $1,500 to $5,000 per month for a small team, which most sub-$1M Shopify stores skip entirely. Ringly runs 24/7 phone support for $349 per month on the Grow plan, which makes "answer the phone when a customer calls about a stockout" a reasonable line item for a $500K/yr supplement brand, not a $10M enterprise. Pair a clean reorder point with a phone channel for the misses, and stockout cost drops from a five-figure monthly risk to a four-figure one.

The reorder point also sits next to pricing decisions. Our markup calculator shows how much room you have in each product. If your markup is thin, the holding cost of a higher service level eats your margin. If your markup is fat, pushing from 95 to 99 percent service level is cheap insurance. Both numbers should be reviewed together every quarter, alongside your average order value.

Start a 14-day free trial of Ringly to see how AI phone support reduces stockout loss.

Frequently asked questions

What is the reorder point formula?

Reorder Point = (Average Daily Sales x Lead Time in Days) + Safety Stock. Safety Stock = Z x sqrt(Lead Time) x Standard Deviation of Daily Sales, where Z is the service-level factor (1.65 for 95 percent, 1.96 for 97.5 percent, 2.33 for 99 percent). The calculator above does the math and stress tests the result against demand spikes and lead-time stretches.

How do I calculate safety stock?

Multiply your service-level Z-score by the square root of lead time by the standard deviation of daily sales. For 95 percent service level on a 21-day lead time with daily sales std dev of 12: safety stock = 1.65 x sqrt(21) x 12 = 91 units. The square root of lead time is what people miss; safety stock does not scale linearly with lead time, it scales with the square root, because variability averages out over longer windows.

What is a good service level for a Shopify store?

95 percent is the default for most Shopify DTC brands. Supplements, CBD, and subscription products typically run 97.5 to 99 percent because a single stockout often drops customer LTV by a full churn cycle. Apparel and food brands often run at 90 to 95 percent because holding cost matters more and stockouts are easier to recover from. The optimal-service-level mode in the calculator picks the right Z for you, based on your stockout cost vs holding cost.

How do I estimate daily sales variability if I do not track it?

If you leave the std dev field blank, the calculator defaults to 30 percent of your average daily sales, which matches typical Shopify stores in our data. For a cleaner number, export 30 to 90 days of daily unit sales from Shopify, drop them in a spreadsheet, and run STDEV.P. High-growth and launch-heavy brands see std dev closer to 50 percent of average, so a blank-default estimate will slightly underprotect you.

What is Economic Order Quantity (EOQ) and how does it relate?

EOQ is the order size that minimizes total holding and ordering costs. Reorder point tells you when to place a PO. EOQ tells you how large the PO should be. They work together. A reorder point without an EOQ leaves you ordering too often or too much. A practical shortcut for Shopify: order 30 to 60 days of expected sales per cycle, or enough to cover the time between when your PO arrives and your next reorder point hit.

How much does a stockout actually cost?

It depends on the category. Supplements and CBD lose the most per unit ($18 to $20) because stockouts break subscription LTV and MAP pricing prevents discount-based recovery. Beauty sits around $12. Pet products around $15. Apparel $8. Food $5. Electronics can hit $25 because comparison shopping is one click away. The calculator uses these benchmarks to show your monthly stockout risk in dollars, not just in units.

How does phone support reduce stockout costs?

Stockouts drive 8 to 12 percent of inbound support calls. Questions like "Is this in stock?" or "When is the restock?" If a customer cannot reach anyone, most of them bounce and buy the substitute. Ringly answers these calls 24/7, takes the customer's email, logs the stockout in your Shopify admin, and routes the customer to a pre-order or substitute. Internal Ringly data shows phone-based restock alerts recover 40 to 55 percent of otherwise-lost customers, which is why the stockout risk in the calculator drops when you tick the phone support checkbox. See our breakdown of AI phone support for Shopify for more.

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