Free valuation & inventory tool
Reorder Point Calculator with Safety Stock and EOQ
The reorder point formula is average daily usage times lead time in days, plus safety stock. If you use 4 filler syringes a day, your supplier takes 3 days and you keep 7 syringes of safety stock, the reorder point is 4 × 3 + 7 = 19 syringes. This reorder point calculator also works out safety stock from your service level and the economic order quantity (EOQ) for how many to order.
Prepared by Prospyr · Reviewed October 3, 2026 · Free, no sign-up, runs in your browser
Examples only. Replace every number with your own usage.
Order placed to product on your shelf.
From your usage log. Higher means less predictable.
Share of reorder cycles without a stockout.
Order quantity (EOQ) inputs
Shipping, staff time, fees per order.
Cost of money, storage, shrink, expiry.
Adds a warning if an EOQ order would outlast it.
Reorder point
17syringes
When on-hand stock reaches 17 syringes, place the next order. Exact value 16.27, rounded up.
Used during lead time
12 syringes
Safety stock
4.3 syringes
Order quantity (EOQ)
37 syringes
Orders per year
32.9
about every 9 days
A math aid for ordering. Follow manufacturer storage and expiry rules; cold-chain products have storage limits and expiry dates that cap how much you should hold.
Reorder point formula and safety stock calculator
- Lead-time demand = average daily usage × lead time (days)
- Safety stock = z × σdaily × √lead time (days)
- Reorder point = lead-time demand + safety stock
This is the simple form where lead time is steady and daily usage varies. Wikipedia's safety stock article gives the fuller formula that also allows lead time to vary, and cautions that no universal formula exists. The tool rounds the reorder point up to whole units so you do not order a fraction too late.
| Service level | z-score |
|---|---|
| 90% | 1.282 |
| 95% | 1.645 |
| 97.5% | 1.960 |
| 99% | 2.326 |
EOQ calculator: how many to order
The reorder point says when to order. Economic order quantity says how much:
- EOQ = √(2 × D × K ÷ h), where D = annual units, K = cost per order, h = holding cost per unit per year
- Holding cost per unit = unit cost × holding rate (cost of money, storage, shrink)
EOQ assumes constant demand, one item per order, a fixed cost for each order and a holding cost per unit. It will not know about volume discounts, case packs or expiry, so treat it as a starting point and round to a size your supplier sells.
Worked examples: filler syringes and toxin vials
| Item | Usage / lead time | Safety stock | Reorder point | EOQ |
|---|---|---|---|---|
| Filler syringes | 4 per day, 3 days | 1.645 × 1.5 × √3 = 4.3 | 12 + 4.3 = 16.3, order at 17 | √(2 × 1,200 × $20 ÷ $36) = 36.5, about 37 |
| Filler syringes, manual buffer | 4 per day, 3 days | 7 (entered) | 12 + 7 = 19 | n/a |
For syringes at $180 each with a 20% holding rate, holding cost is $36 per unit per year, and 300 open days at 4 per day is 1,200 syringes a year. EOQ is about 37 syringes per order, or roughly 9 days of usage. All numbers are examples for the math; use your own usage, lead time and costs.
Keeping the numbers current
A reorder point is only as good as the usage figure behind it. Re-check it each quarter and after you add a provider or a service. Prospyr's inventory management tracks injectables down to the unit, tied to the appointments where they were used, so average usage comes from records instead of memory. To see whether stock is moving at all, use the inventory turnover calculator.
Frequently asked questions
What is the reorder point formula?
Reorder point = (average daily usage × lead time in days) + safety stock. It is the stock level at which you place a new order so that the delivery arrives before you run out. Wikipedia states it as normal consumption during lead time plus safety stock.
How do you calculate safety stock?
A common formula is safety stock = z × standard deviation of daily usage × square root of lead time in days, where z comes from your target service level. At a 95% service level z is 1.645. With a daily variation of 1.5 and a 7-day lead time, safety stock is 1.645 × 1.5 × 2.646 = 6.5 units.
What is the EOQ formula?
Economic order quantity = the square root of (2 × annual demand × cost per order ÷ annual holding cost per unit). It finds the order size that balances ordering costs against the cost of holding stock. Ford W. Harris published the model in 1913.
Does EOQ work for botulinum toxin or other products that expire?
Use it with care. EOQ assumes steady demand and does not know about expiry dates. The optional shelf life field warns you when an EOQ order would last longer than the product's shelf life; in that case order less, more often. Follow the manufacturer's storage and expiry limits.
How do I find my average daily usage and its variation?
Pull 8 to 12 weeks of usage by day (units used, divided by days you were open) and average it. The standard deviation is the spread of those daily numbers, and a spreadsheet function such as STDEV does it. If you do not have the data yet, enter safety stock manually from a rule you trust and revisit it.
What service level should I pick?
Service level is the share of reorder cycles in which you do not run out. 95% means you expect a stockout in about 1 cycle in 20. Higher levels need more safety stock, so use a higher level for items a missed appointment depends on and a lower one for items you can substitute.
Sources and scope
- Reorder point. Wikipedia
States the reorder point as consumption during lead time plus safety stock, and the usage-times-lead-time form.
- Safety stock. Wikipedia
Gives ROP = lead time × demand + z × σ × √L for steady lead time, z = 1.65 for a 95% service level, and the caution that no universal formula exists.
- Economic order quantity. Wikipedia
Gives Q* = √(2DK/h), the 1913 Ford W. Harris attribution and the model's assumptions (constant demand, fixed order cost, holding cost per unit).
A math aid for ordering, not purchasing, clinical or regulatory advice. Follow manufacturer storage, handling and expiry rules for every product.