نقطه سفارش مجدد و موجودی اطمینان

Two mistakes do not cost the same, but both cost money: a warehouse full of slow-moving stock, and an empty shelf of what the customer wanted today. The gap between them is one number: the stock level at which you should place the next order.

This tool computes reorder point: usage during lead time plus safety stock for sales variability and supplier delay. If you also enter holding cost and cost per order, it tells you how much to order each time to minimize the sum of those two costs—and a sensitivity table shows how many extra units the latest service level requires.

• Enter average daily sales directly, or the tool builds it from period sales ÷ period length. Only one of these two ways.
• Safety stock, when you have also given lead-time volatility, is calculated with the full formula: z × √(lead time × daily sales volatility² + average daily sales² × lead-time volatility²). When you have not, with the simple formula z × daily sales volatility × √(lead time). The result states explicitly which one was used.
• z is the service-level z-score on the standard normal (one-sided): 90% → 1.2816, 95% → 1.6449, 98% → 2.0537, 99% → 2.3263.
• Reorder point = average daily sales × lead time + safety stock. If you give current stock, days left until that point = (current stock − reorder point) ÷ average daily sales.
• Economic order quantity = √(2 × annual demand × cost per order ÷ annual holding cost per unit), and is shown only when you have entered both costs; the tool guesses no costs.
• If you do not have the standard deviation of daily sales and instead enter the highest daily sales of the past month, the tool takes (max − average) ÷ 2 as an approximation — because with about 30 observations, the maximum usually falls near two standard deviations above the mean. This is a rough approximation, not a measured standard deviation, and the result says so.
• All inventory quantities round up: 44.1 units means 45 units. Rounding down quietly lowers the service level you asked for.

• All formulas assume daily demand is roughly normal and days are independent. Seasonal, campaign, and newly launched products break this assumption; for them these numbers are a starting point, not an answer.
• Service level is the chance of not stocking out in one lead-time cycle — not an annual guarantee and not a share of orders. At 95% with 12 orders a year, on average 0.6 cycles in the year see a stockout.
• If daily sales volatility is greater than the mean itself, demand is "lumpy" and the normality assumption weakens; the tool warns and the safety-stock figure should be treated as a ceiling, not exact.
• Economic order quantity, supplier volume discounts, warehouse space, minimum order quantity, and purchase-price inflation are not included. When purchase prices rise quickly, a larger order can beat EOQ; that decision is outside this tool.
• Input figures should come from your own actual sales. Search interest, page views, or mental estimates are not sales measurements and should not be entered instead.
• This tool is a calculator, not advice: none of the figures recommend buying, pricing, or investing.