What Is a Reorder Point?
A reorder point (ROP) is the inventory level that signals when to place a new purchase order. It covers the units you expect to sell while waiting for replenishment, plus safety stock to protect against higher demand or a late delivery.
For Shopify stores, a useful ROP can reduce lost sales without tying up too much cash in extra products. Reorder points are estimates, not guarantees: review them when sales patterns, supplier lead times, or seasonal demand change.
Reorder Point Formulas
The basic formula is:
Reorder Point = (Average Daily Sales × Lead Time in Days) + Safety Stock
A common estimate of safety stock using peak demand and maximum lead time is:
Safety Stock = (Maximum Daily Sales × Maximum Lead Time)
− (Average Daily Sales × Average Lead Time)
A statistical approach uses demand variability and a service-level factor:
Safety Stock = Z × Standard Deviation of Demand During Lead Time
The Z value represents the chosen service level; for example, 95% corresponds to about 1.65 under a normal-distribution model. Reorder point is not the same as order quantity: use the Economic Order Quantity (EOQ) Calculator to estimate how many units to buy when you place an order.
How to Use This Calculator
- Enter Average Daily Sales — the average number of units sold per day. Use a representative period, and avoid letting a one-day promotion define your normal rate.
- Enter Lead Time Days — the usual number of days from placing the PO to receiving sellable stock, including supplier processing and transit.
- Enter Lead Time Variation — the maximum lead time in days you have experienced or reasonably expect. This helps account for supplier and shipping delays.
- Enter Max Daily Sales — the highest daily unit sales you have seen. This helps represent demand spikes.
- Enter Unit Cost and Selling Price — use your per-unit COGS and customer price to estimate inventory value and the revenue exposed to a stockout.
- Set Holding Cost % — estimate annual storage, insurance, handling, and cost-of-capital expenses as a percentage of unit cost. A 20–30% annual rate is a common planning assumption, not a universal rule.
- Choose Service Level — select the desired probability of avoiding a stockout during lead time. Compare the calculator’s service-level results against the cost of carrying the extra buffer.
Use consistent units and update the inputs when your sales or supplier data changes. For detailed safety-stock scenarios, compare the result with our Safety Stock Calculator.
Step-by-Step Example
Suppose a Shopify store sells 8 insulated lunch bags per day on average. Its usual replenishment lead time is 10 days, but deliveries can take up to 13 days; peak demand has reached 12 bags in one day.
Using a conservative maximum-demand estimate:
| Calculation | Arithmetic | Result |
|---|---|---|
| Expected demand during average lead time | 8 × 10 | 80 bags |
| Demand during peak conditions | 12 × 13 | 156 bags |
| Estimated safety stock | 156 − 80 | 76 bags |
| Reorder point | 80 + 76 | 156 bags |
At a unit cost of $11, the reorder-point inventory is worth 156 × $11 = $1,716 at cost. If the selling price is $32, one day of average sales represents 8 × $32 = $256 in potential revenue. These are planning estimates; a service-level comparison helps you decide whether this buffer is appropriate for the product.
Choosing a Service Level and Managing the Tradeoff
A service level is the target probability of having stock available throughout replenishment lead time. Higher targets can reduce stockouts, but they require more safety stock and more cash tied up in inventory.
| Product role | Starting service-level target | Why it may fit |
|---|---|---|
| Core best-seller or gift-season item | 97–99% | A missed sale may also send a ready-to-buy customer to a competitor. |
| Reliable, steady seller | 94–97% | Balances availability against the cost of carrying extra units. |
| Slow-moving or easily substituted item | 90–94% | Lower demand risk may not justify a large buffer. |
These are planning ranges, not universal industry averages. A 99% target is not automatically better: the additional inventory may cost more to store than the sales it protects. Compare the carrying cost with the expected cost of stockouts, then test different service levels in the calculator.
Inventory also uses working capital that could fund marketing, payroll, or other purchases; the U.S. Small Business Administration’s cash-flow guidance explains why businesses need to plan cash coming in and going out. For retail context, the U.S. Census Bureau’s retail trade data tracks sales and inventories, but national figures should not replace your product-level sales and lead-time history.
6 Tips to Improve Reorder Decisions
- Test a higher service level on one proven best-seller. Change the target from 95% to 99%, then compare the added stock value with the sales you might protect.
- Use a separate peak-season sales rate. If a product typically sells 6 units daily but reaches 15 in December, calculate a seasonal ROP before the promotion period rather than relying on the annual average.
- Measure actual supplier lead times. Record the PO date and sellable-receipt date for each shipment; if deliveries range from 9 to 17 days, use that history to revisit your lead-time assumptions.
- Include all costs in your holding-cost estimate. Add storage, insurance, handling, and financing costs instead of counting only warehouse rent.
- Review products with repeated stockouts. Compare their lost-sales exposure with safety-stock costs using the Stockout Cost Calculator.
- Check inventory health before increasing every reorder point. A high ROP can worsen overstock on slow sellers; use the Inventory Turnover Calculator to spot products that sit too long.
Frequently Asked Questions
What is a reorder point and how is it calculated?
The reorder point (ROP) is the inventory level at which you should place a new purchase order. The formula is ROP = (Average Daily Sales × Lead Time) + Safety Stock; for example, 12 × 14 = 168, then 168 + 30 = 198 units. When inventory drops to 198, place a PO to reduce the risk of running out before replenishment arrives.
How do you calculate safety stock?
Safety stock is buffer inventory that protects against demand spikes and supplier delays. A statistical formula is Safety Stock = Z × σ, where Z is the service-level factor (about 1.65 for 95%) and σ is the standard deviation of demand during lead time. This approach accounts for demand variability and, when modeled, lead-time variability.
What service level should I use for safety stock?
A 95% service level is a common starting point, meaning the model targets enough stock to meet demand during lead time in 95% of cases. Use a higher target for products where stockouts are especially costly and a lower one for slow-moving items with expensive carrying costs; moving from 95% to 99% raises the Z factor from about 1.65 to 2.33, not by the same percentage as the service-level change.
How much does a stockout cost?
A basic estimate is lost daily sales × selling price: at 12 units per day and $45 each, 12 × $45 = $540 in potential revenue per day. The broader impact can include customers switching to competitors, wasted advertising, and reduced product visibility; use the Stockout Cost Calculator to assess costs beyond direct lost sales.
How often should I recalculate reorder points?
Recalculate monthly for most products and more often for fast-moving or seasonal items. Update the inputs when sales velocity or supplier lead times shift, and review them before peak seasons; inventory software can automate alerts, but the underlying assumptions still need periodic checks.
About This Calculator
The Reorder Point Calculator was built by Luis Dev Studio for Shopify merchants managing product availability and inventory costs. For help applying reorder planning to your store, contact us or explore our services.
Updated by Luis Gonzalez · Sep 18, 2026