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Inventory reorder point calculator

Reorder when your stock falls to what you will sell before the new stock arrives, plus a buffer. Enter your sales and lead time to find that level.

Units sold over the last 30 to 90 days, divided by the number of days.

From placing an order to having the stock ready to sell.

Your buffer in units. The safety stock calculator works it out; empty means none.

Sellable stock plus open purchase orders, minus orders not yet shipped.

What each purchase order costs whatever its size: admin, inbound delivery, receiving.

Storage, insurance, shrinkage and the cost of cash tied up in the unit.

Result

Fill in average units sold per day, lead time to see the result.

How it works

An order takes time to arrive, and you keep selling while it is on its way. So you have to place it while you still hold enough stock to cover the wait. That level is the reorder point: the sales you expect during the lead time, plus safety stock for the cycles when sales run fast or the delivery runs late.

Add your order and holding costs and the calculator also gives the economic order quantity: the order size that keeps the cost of ordering plus the cost of holding stock lowest.

lead-time demand = units sold
  per day × lead time in days
reorder point =
  lead-time demand + safety stock

days of stock = stock ÷ units per day
days to the reorder point =
  (stock - reorder point)
  ÷ units per day

economic order quantity =
  √(2 × yearly demand
    × cost per order
    ÷ holding cost per unit per year)

What each term means

Units sold per day
Units sold over a recent normal period divided by its days. Leave out days you were out of stock, which understate demand.
Lead time
Days from placing an order to having the stock ready to sell: production, transit, customs and receiving.
Safety stock
Your buffer in units. The safety stock calculator works it out from a service level.
Units in stock and on order
Sellable stock plus open purchase orders, minus orders not yet shipped.
Cost to place one order
What each purchase order costs whatever its size: admin time, inbound delivery, receiving.
Cost to hold one unit for a year
Storage, insurance, shrinkage and the cost of the cash tied up in the unit.

Which variant: a reorder point for continuous review, where you check stock often and order when it reaches the point. Safety stock is your input; the safety stock calculator computes it as z × the standard deviation of daily sales × √lead time. The EOQ is the classic Harris-Wilson model: steady demand, a fixed cost per order, and a store that sells on 365 days a year.

Sources: Wikipedia, Reorder point (read 26 September 2026) and Wikipedia, Economic order quantity (read 26 September 2026).

Worked example

Example numbers, round on purpose, not a real store:

Average units sold per day
30
Lead time
21 days
Safety stock
150 units
Units in stock and on order
1,200
Cost to place one order
€60
Cost to hold one unit for a year
€3
  1. 1Lead-time demand: 30 × 21 = 630 units
  2. 2Reorder point: 630 + 150 = 780 units
  3. 3Days of stock: 1,200 ÷ 30 = 40 days
  4. 4Days to the reorder point: (1,200 - 780) ÷ 30 = 14 days
  5. 5Yearly demand: 30 × 365 = 10,950 units
  6. 6Economic order quantity: √(2 × 10,950 × €60 ÷ €3) = √438,000 = 662 units, about 16.5 orders a year

So this example reorders in two weeks, when 780 units are left, and orders about 660 units at a time.

Frequently asked questions

  • What is a reorder point?
    The stock level at which you place the next order: the units you expect to sell while the order is on its way, plus safety stock. Order when your stock falls to it, and the new stock should arrive before you run out.
  • How much safety stock should I hold?
    Enough to cover the gap between average and bad-case demand during the lead time, at the service level you choose. The safety stock calculator works it out from how much your daily sales and lead times vary. A fixed number of days of cover is simpler, but it is not tied to any stockout risk.
  • Should I count stock that is already on order?
    Yes. Compare the reorder point with your stock on hand plus open purchase orders, minus orders you still have to ship. Otherwise you may order again while a delivery is already on its way.
  • What is the economic order quantity?
    The order size that makes the yearly cost of placing orders plus the yearly cost of holding stock as low as it can be: the square root of 2 × yearly demand × cost per order ÷ yearly holding cost per unit. It assumes steady demand and a fixed cost per order, so round it to your supplier's case sizes or minimum order.
  • How do I estimate the cost of holding a unit for a year?
    Add up what storing it costs (space, handling, insurance), what can go wrong with it (damage, theft, going out of date or out of season) and what the cash tied up in it could have earned elsewhere. It is often estimated as a share of the unit's cost; use your own figures where you have them.
  • What if my sales are seasonal?
    Use the daily sales you expect during the lead time, not a yearly average. Recalculate the reorder point before each season, and for products that are growing fast, from the most recent weeks.

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