Reorder Point Calculator
Free, in-browser. The full statistical reorder point — lead-time demand plus safety stock computed from both demand variability and lead-time variability — with pack-size rounding and an order-now check against your current inventory position. Nothing leaves your machine.
The formula
ROP = (daily demand × lead time) + z × σ_LTD σ_LTD = √(LT × σ_d² + d² × σ_LT²)
The first term is what you expect to sell while the replenishment order is in transit. The second is safety stock: the buffer sized to your chosen service level (z) against the combined variability of demand and lead time. Most POS reorder features — and most spreadsheets — skip the σ terms entirely and use a hand-picked threshold, which is why best sellers still stock out. The order check compares the ROP against your inventory position(on hand + already on order), not just what's on the shelf — forgetting inbound POs is the classic double-order.
How to use this
- Pull average daily sales and the standard deviation from your POS (last 30–90 days; Excel:
=AVERAGE(...)and=STDEV.S(...)). - Use the supplier's actual lead time from recent orders, not the promised one — and its variability if deliveries wobble.
- Pick a service level: 95% is a sound default; 99% for items whose stockout costs real revenue (see stockout cost).
- Enter what's on hand and on order, and the tool tells you whether to order now and how much, rounded to your pack size.
One item, once, is a worksheet. Every item, every night, with demand and lead times measured from your actual sales and supplier history — that's what LineNow does, and the reorder point becomes a sent purchase order instead of an alert. Free for 90 days, $100/month after.