Simulator
Enter the current state and Lean target
Core logic: Annual holding cost = inventory value x carrying-cost rate
Calculator Library / Inventory
Inventory and Waste Cost Simulator
Translate inventory levels, flow assumptions, and lead time into annual holding cost, Lean savings potential, and a Kanban quantity recommendation that accounts for demand variability.
Breakdown
Savings scenario
| Source | Amount | Share |
|---|---|---|
| Inventory reduction | $24,624 | 46.2% |
Kanban
Recommendation detail
Kanban formula: daily demand x replenishment lead time + safety stock, all divided by container quantity.
Safety stock factor: demand variability and the chosen service factor drive the protection level.
Lean target inventory after reduction: 8,400 units
Instructions
How to use this app
- Enter current inventory, unit cost, annual throughput, holding-cost rate, and current lead time.
- Set the Lean scenario reductions for inventory, lead time, batch size, and pull-system waste improvement.
- Click `Simulate` to calculate annual holding cost and projected recurring Lean savings.
- Enter container quantity, demand variability, replenishment lead time, and service factor to generate a Kanban recommendation.
- Use the outputs together: annual holding cost frames today’s waste, while the savings and Kanban guidance show how a pull-based future state could change it.
The Kanban card count is directional. If you have strong seasonality, highly variable supplier performance, or mixed-model replenishment, you should validate the recommendation against real replenishment history.
Batch-size and pull gains are modeled as additional recurring savings levers layered on top of direct inventory and lead-time improvements. Adjust them conservatively when you are early in the project.
What This Inventory and Waste Simulator Helps You Quantify
This tool turns excess inventory into financial language. It estimates annual holding cost, highlights Lean waste tied to overproduction and long replenishment loops, and helps teams test how smaller batches or pull-based replenishment change the cost profile.
Use it when inventory feels normal because it has been there a long time, but leadership needs a clearer view of carrying cost, delay risk, and potential savings.
Core Inventory Logic
| Metric | Formula or Logic | Meaning |
|---|---|---|
| Annual holding cost | Average inventory value x Holding-cost rate | Financial cost of carrying inventory over time. |
| Lead-time exposure | Demand x Replenishment delay | How much stock the system needs to cover replenishment lag. |
| Kanban quantity | Demand during lead time + safety factor | Signal-based replenishment target for pull systems. |
Worked Example
If a work center carries $250,000 of average inventory and the holding-cost rate is 22%, the carrying burden is $55,000 per year before obsolescence, extra handling, or schedule distortion are fully counted. Reducing batch size or replenishment delay may cut that burden quickly without touching sales.
The simulator helps frame inventory reduction as a business decision rather than a visual housekeeping exercise.
How to Interpret the Results
- High holding cost: the system is paying a large premium for slow flow.
- Large Kanban quantity: demand variability or lead-time delay is still too high.
- Strong savings from batch reduction: setup, flow, and replenishment design deserve review.
- Little savings from small changes: the real constraint may be supplier delay or internal instability.
Inventory and Waste Frequently Asked Questions
Why is inventory treated as waste in Lean?
Because inventory hides problems, consumes cash, increases handling, and delays the visibility of defects or imbalance in the system.
What is included in holding cost?
Typical holding cost includes capital, storage, handling, insurance, shrinkage, and obsolescence risk.
Can inventory reduction create new risk?
Yes. If lead time, changeover, or process instability is not addressed, reducing inventory too early can simply expose a weak system faster.
Why does demand variability matter for Kanban sizing?
Because a pull loop must absorb normal variation. Without that adjustment, the signal quantity may look lean on paper but fail in practice.
What is the most common inventory-reduction mistake?
Cutting stock without fixing the flow drivers beneath it. Inventory should be reduced as the system becomes more stable, not as a slogan by itself.
Related Templates and Guides
Download the Standard Work Template
Use standard work to stabilize replenishment tasks, material handling, and line-side routines after inventory changes are made.
Read the Value Stream Mapping Guide
Use the guide to connect inventory cost back to flow delay, queue size, and the current-state map.