Inventory / Free calculator
Inventory Reorder Calculator
Estimate stock cover, reorder timing and replenishment quantities using daily demand, lead time, safety stock and dated incoming inventory.
Set up your scenario
Let’s run the numbers.
Your result updates as you enter valid inputs. See how it’s calculated.
Confirmed incoming inventory (optional)
Understand the numbers
How this calculator works
On-hand cover = stock ÷ daily demand. Reorder threshold = daily demand × lead time + safety stock. Reorder timing projects the first threshold crossing along constant demand and dated receipts. Order-up-to level = demand × (lead time + review period) + safety stock. Suggested quantity starts with ceiling of max(0, order-up-to level − usable stock − confirmed receipts within that period), then increases if needed to protect safety stock before a later receipt arrives. The new order is assumed to arrive after the entered lead time.
See the method in practice
Worked example
With 500 usable units, demand of 10/day, 30-day lead time, 100 safety units and a 7-day review period, on-hand cover is 50 days. Reorder threshold is 400 units, reached in 10 days. The current order-up-to level is 470, so no replenishment is needed today. With only 300 on hand, the suggestion becomes 170 units.
Assumptions and limitations
Constant demand, deterministic lead time, no backorders, minimum order quantities or pack sizes. Receipts are assumed usable at the start of their arrival day. Late receipts do not reduce the current suggested order. A receipt after an earlier threshold crossing does not postpone that initial alert. Review-period stock protection is used for quantity; timing uses the continuous-review threshold. An order arriving after projected stockout requires a separate expedite decision.
A little help with the inputs
Input guide
Use consistent currencies, units and periods. Select a field for its definition.
Usable stock (units)
Sellable units on hand; exclude damaged or already committed stock.
Average daily demand (units/day)
Use a representative period and adjust for known changes.
Supplier lead time (days)
Order placement through sellable receipt, including transit and receiving.
Safety stock (units)
Your chosen buffer, not a statistically estimated service level.
Review period (days)
Days between ordering reviews; 0 for continuous review.
Before you make your next move
Frequently asked questions
Does incoming stock prevent a stockout?
Only if it arrives before the projected shortage. The calculator separately shows first projected stockout timing and counts only receipts inside the protection period toward the current quantity.
What if demand is zero?
Stock cover has no finite value. There is no demand-driven depletion; a safety-stock shortfall can still justify replenishment.
Do I have to share my data or email address?
No. Core results and exports work without an account or email. An enquiry is optional, with a separate unchecked choice to share an aggregate summary. Raw report rows stay local.
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