Inventory pulse rail, reorder threshold, and supplier arrivalsTriangles mark orders placed; green vessels mark the month each order arrives
Business
Supplier Order Forecast Calculator
Create a rolling supplier-order plan from demand, growth, seasonality, lead time, safety stock, order quantity, opening purchase orders, and inventory position. Each month receives due orders, fulfills available demand, records lost sales, and decides whether another order is required. The result includes stockout months, service level, average inventory, purchase cash, ending inventory, and a detailed order-and-arrival ledger.
Purchase orders placed-
Purchase cash committed-
Service level-
Stockout months-
Lost sales units-
Ending on-hand inventory-
Average inventory-
Fulfilled revenue-
Inventory pulse and inbound vessels
Watch demand draw stock down while purchase orders travel through lead time
On-hand inventoryDemand and lost salesInbound arrivals
| Month | Opening | Arrivals | Demand | Fulfilled | Lost sales | Ending | Inventory position | Order placed | Purchase cash |
|---|
Supplier-order planning method
Use inventory position for ordering and on-hand stock for fulfillment
- Enter opening on-hand inventory separately from purchase orders already in transit.
- Forecast monthly demand with growth and a seasonal index appropriate to the product.
- Calculate lead-time demand and add safety stock to form the rolling reorder point.
- Place a fixed-lot supplier order when inventory position reaches the threshold.
- Receive each purchase order after lead time, fulfill available demand, and record lost sales rather than hidden negative inventory.
Inventory-control notation
Demand, position, and physical stock answer different questions
Detailed calculation process
Forecast the threshold ahead, then move each order to its arrival month
D_m = D_1 * (1 + g)^(m - 1) * [1 + s * sin(2π(m - 2) / 12)]Lead-time demand_m = sum(D_(m + 1) ... D_(m + L))ROP_m = Lead-time demand_m + SS Available_m = Opening inventory_m + Arrivals_mFulfilled_m = min(Available_m, D_m)Lost sales_m = D_m - Fulfilled_mEnding inventory_m = Available_m - Fulfilled_m Inventory position_m = Ending inventory_m + Open purchase orders_mIf Inventory position_m <= ROP_m, place Q units for arrival in month m + LPurchase cash_m = Ordered units_m * C Worked default reorder
The first new supplier order is placed in month 2 and arrives in month 4
The default opens with 1,250 units on hand and 600 units already due in month 2. Month-one demand is 430 units before seasonality, demand grows 2.2% monthly, lead time is two months, safety stock is 520 units, and each new order contains 1,800 units.
Month 1 seasonal demand = 430 * [1 + 0.24 * sin(-π / 6)] = 378.4 unitsMonth 1 ending inventory = 1,250 - 378.4 = 871.6 unitsMonth 1 inventory position = 871.6 + 600 inbound = 1,471.6 units Month 2 available = 871.6 + 600 arrival = 1,471.6 unitsMonth 2 fulfilled demand = 439.5 unitsMonth 2 ending = 1,471.6 - 439.5 = 1,032.1 unitsMonth 2 reorder point = 503.0 + 554.4 + 520 = 1,577.4 units Because 1,032.1 units of inventory position are below the 1,577.4-unit threshold, the model places 1,800 units in month 2 for arrival in month 4. Across 18 months the default places six orders, commits about $127,440 of purchase cash, fulfills 100% of modeled demand, and ends with about 1,118.7 units.
Planning data
Inputs worth measuring by SKU
- Demand history after stockout correction
- Supplier lead-time distribution, not only average
- Open purchase orders and confirmed due dates
- Service-level target translated into safety stock
- MOQ, case pack, payment milestone, and unit landed cash
Forecast limitation
Fixed lots and deterministic lead time simplify reality
The model treats unfilled demand as lost, uses one fixed order quantity, pays orders when placed, and assumes deterministic arrivals. It excludes backorders, partial receipts, lead-time variation, quantity discounts, shelf life, multi-location transfers, supplier capacity, and cash receipts from sales.
Supplier order forecast FAQ
Questions about reorder points and stockouts
Why does the model use future lead-time demand?
An order placed today must cover demand that occurs before its replacement stock can arrive.
Can the inventory position be high while on-hand stock is low?
Yes. Inventory position counts open purchase orders, while fulfillment can use only stock physically available in the current month.
What if my supplier requires several case packs?
Enter the economic lot as the order quantity or round the model result to the supplier's required case-pack multiple outside the calculator.
Practical examples
Supplier Order Forecast Calculator in real planning situations
- Plan quarterly imports with a two-month lead time.
- Test whether the reorder point protects a seasonal demand peak.
- Measure cash committed when order quantity exceeds near-term demand.
Important note
Before relying on this result
Calculated from the entered values using the displayed accounting method. Reconcile material decisions with source records and applicable accounting policy.
Additional Supplier Order Forecast Calculator questions
What is inventory position?
It is on-hand inventory plus open purchase orders; reorder decisions use position so the model does not duplicate inbound stock.
Are lost sales backordered?
No. This model treats unfilled demand as lost sales rather than carrying it into a later month.
Why can purchase cash rise before inventory?
Supplier orders are paid when placed while physical inventory arrives after the entered lead time.