Business
Inventory Forecast Calculator
Calculate horizon demand, final demand, whole orders, purchased units, ending inventory, purchase cost, average demand, and coverage. The custom step forecast plots demand drawdown, lot receipts, and the safety-stock floor for each month.
Forecast demand over horizon-
Demand in final forecast month-
Whole replenishment orders required-
Units purchased-
Modeled ending inventory-
Forecast inventory purchases-
Average monthly demand-
Ending inventory coverage at final demand rate-
Decision view
Inventory drawdown and replenishment path
Inventory drawdown and replenishment pathMonthly demand, whole-lot receipts, safety stock, and ending units share one ledger.
Exact scenario comparisonForecast horizon (months) changes while all other entered assumptions remain constant.
| Forecast horizon (months) | Forecast demand over horizon | Demand in final forecast month | Whole replenishment orders required | Units purchased | Modeled ending inventory | Forecast inventory purchases | Average monthly demand | Ending inventory coverage at final demand rate |
|---|
Forecast detail
Monthly inventory forecast and replenishment events
How to use Inventory Forecast Calculator
- Enter usable opening stock, starting monthly demand, growth, safety stock, lot size, unit cost, and horizon.
- Review each modeled receipt against supplier lead time and ordering cadence.
- Stress-test growth, seasonality, delays, minimums, capacity, shelf life, and stockout service targets.
Calculator guide
Understanding Inventory Forecast Calculator
Inventory planning is a month-by-month balance equation: opening units plus receipts minus demand equals ending units. Whole replenishment lots and safety stock make the ordering path discontinuous, so one horizon total is not enough.
Calculation method
How the calculation works
Compound the entered monthly demand assumption through a finite horizon, calculate the whole replenishment lots needed to finish at or above target safety stock, and reconcile opening, purchases, demand, and ending units. Compound demand monthly, consume it from available units, add the minimum whole lots needed whenever projected ending stock falls below safety stock, and carry the balance forward.
Replenishment policy
Translate the forecast into an ordering rule
The model becomes operational only after timing and authority are defined.
Worked situations
Practical examples
- Three percent monthly growth compounds on the prior month's demand.
- A receipt is rounded to a whole lot rather than an exact shortage quantity.
- Ending coverage divides final inventory by final-month demand.
Better inputs
Useful tips
- Use demand net of expected returns and cancellations.
- Separate safety stock from cycle stock and verify both use the same unit.
- Replace the smooth growth assumption with monthly seasonality when demand is event-driven.
Before relying on the result
Limitations and common mistakes
- The model assumes deterministic demand and immediate modeled receipt within each replenishment month.
- Lead time uncertainty, supplier capacity, backorders, lost sales, review periods, multiple SKUs, spoilage, and warehouse limits are excluded.
- A modeled order date is not a purchase recommendation.
Reference
Key terms
- Safety stock
- Target buffer intended to remain after forecast demand.
- Replenishment lot
- Fixed whole quantity received per modeled order.
- Ending inventory
- Opening inventory plus receipts minus demand.
- Coverage
- Ending inventory divided by final-month demand.
Important note
Calculated from the entered values using the displayed accounting method. Reconcile material decisions with source records and applicable accounting policy.
Frequently asked questions
Why can ending stock exceed safety stock?
Whole-lot rounding can add more units than the exact shortage.
Does the forecast model lead time?
No. Receipts are immediate in the modeled month; ordering must be shifted earlier operationally.
Can negative growth be entered?
Yes within input constraints, but demand assumptions should remain nonnegative and realistic.
Is ending coverage a service level?
No. It is a simple months-of-demand ratio, not a stockout probability.