Enter Inventory Inputs
Use the responsive grid below. Large screens show three columns, medium screens show two, and mobile screens show one.
Inventory Planning Graph
The chart compares lead-time demand, safety stock, reorder point, cycle stock, and average inventory. It reflects your latest calculation, or the default example before submission.
Example Data Table
These example scenarios show how the calculator behaves under different operating conditions.
| Scenario | Method | Avg Daily Demand | Avg Lead Time | Service Level | Safety Stock | Reorder Point | EOQ |
|---|---|---|---|---|---|---|---|
| Steady demand | Demand variability only | 80.00 | 7.00 days | 90.00% | 33.91 | 593.91 | 1,359.74 |
| Balanced uncertainty | Normal distribution with demand and lead-time variability | 120.00 | 9.00 days | 95.00% | 404.63 | 1,484.63 | 1,409.61 |
| Volatile replenishment | Max-minus-average heuristic | 60.00 | 10.00 days | 97.00% | 920.00 | 1,520.00 | 1,085.44 |
Formula Used
The normal method is best when both demand and lead time fluctuate and you want a probability-based buffer. The demand-only method works when supplier lead time is stable. The heuristic method is practical when only average and maximum observations are available.
EOQ is optional but useful for policy alignment. It helps compare your current order quantity with a cost-balanced replenishment size.
How to Use This Calculator
- Enter average daily demand and average lead time first. These are the core drivers of lead-time demand.
- Add variability measures. Demand and lead-time standard deviations improve the normal calculation.
- Choose a service level. Higher percentages reduce stockout risk but increase inventory.
- Select a method. Use normal for analytical planning, demand-only for stable lead times, or the heuristic method when only extremes are known.
- Enter order quantity, unit cost, carrying rate, and ordering cost if you want EOQ and holding-cost analysis.
- Press the calculate button. The result appears above the form, directly below the header.
- Review the chart, result table, and interpretation text to validate the replenishment policy.
- Download CSV for spreadsheet work or PDF for reporting and sharing.
FAQs
1) What is a reorder point?
A reorder point is the stock level that triggers a new order. It combines expected lead-time demand with a protective safety stock buffer.
2) What does safety stock protect against?
Safety stock protects against uncertainty. It absorbs higher-than-expected demand, longer supplier lead times, or both, reducing the chance of stockouts.
3) Which method should I choose?
Choose the normal method when you have standard deviations and want a service-level based result. Use demand-only when lead time barely changes. Use the heuristic option when only average and maximum observations are available.
4) Why does a higher service level increase inventory?
A higher service level means you want fewer stockouts. That requires a larger z-score and more safety stock, which raises average inventory.
5) Is EOQ required for reorder point calculations?
No. Reorder point and safety stock can be calculated without EOQ. EOQ simply helps you compare replenishment size against ordering and carrying costs.
6) Can I use weekly demand instead of daily demand?
Yes, but keep units consistent. If demand is weekly, then lead time and variability measures should also be expressed in weeks.
7) What if I do not know standard deviation?
You can use the heuristic method with average and maximum values. It is less statistical, but still useful for practical planning when data is limited.
8) Does this calculator work for all industries?
Yes. The logic is general and works for retail, manufacturing, distribution, healthcare, spare parts, and any stock-controlled environment with recurring demand.