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Replenishment Quantity Calculator
Estimate how many units to order using demand, lead time, review period, safety stock, stock on hand, incoming stock and backorders.
What does this calculator measure?
Replenishment quantity is the stock needed to bring your inventory position up to a target level. In this periodic-review calculator, the target covers demand during supplier lead time plus the time until the next review, with an added safety stock buffer.
Enter your figures
Use one consistent period. Calculations run locally in your browser.
Average units needed per day; fractional averages are allowed.
Days from placing an order to usable stock arriving.
Days until the next stock review; use the same calendar basis as lead time.
Extra buffer for demand and supply variability.
Current usable stock, before subtracting the backorders below.
Confirmed incoming units expected within the planning horizon.
Outstanding demand not yet shipped; do not deduct it twice.
Your result
Fill in all fields or load the worked example to see your result.
Put your figures to work
Turn your replenishment review into a purchasing workflow with stock records and purchase orders.
Start managing inventoryFormula and worked example
Target stock = Daily demand × (Lead time + Review period) + Safety stock. Inventory position = On hand + On order − Backorders. Order quantity = max(0, Target stock − Inventory position), rounded up.
At 10 units per day, a 7-day lead time, a 7-day review period and 30 safety units, target stock is 170. With 80 on hand, 40 on order and 10 backordered, inventory position is 110. Suggested replenishment is 60 units.
How to use the calculator
- Choose the product, category or business and the period you want to review.
- Enter the figures described beside each field using consistent units.
- Review the result alongside the assumptions below before changing purchasing or stock plans.
How to interpret your result
This is an order-up-to estimate for steady average demand. It is different from EOQ, which balances ordering and holding costs, and reorder point, which determines when to order. Check supplier minimum quantities, pack sizes, expiry dates, delivery timing and storage limits before buying. Incoming stock arriving too late should not be counted as available within this horizon.
Explore the inventory workflow in My Inventory ItemsFrequently asked questions
Why include a review period?
In periodic review, you need stock to cover both the supplier lead time and the interval before you review and order again. The review period extends the demand coverage horizon.
Why subtract incoming stock?
Confirmed incoming stock increases inventory position and reduces the additional amount needed. Include only orders expected to arrive within the planning horizon.
What does an order quantity of zero mean?
Your inventory position already meets or exceeds the calculated target. This model suggests no extra units based on the entered assumptions; it does not guarantee there will be no stockout.