Online Tool Store
Inventory Buffer Calculator
Inventory Buffer Calculator shows which variability is driving your buffer — usually the supplier's, which is negotiable in a way demand is not.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Finance
Inventory Buffer Calculator
Frontend preview — no upload or external service.
Safety stock
At a 95% service level, safety stock of about 480 units and a reorder point of 1,500. Lead time variability contributes more to that buffer than demand variability does.
How the Inventory Buffer Calculator works
- Enter average demand and its variability, and the same for lead time.
- Set a service level. Going from 95% to 99% roughly doubles the safety stock for a modest reduction in stockouts.
- Look at which source of variability dominates. Reducing lead time variability is usually cheaper than carrying the stock it forces you to hold.
The method
Safety stock covers variability in both demand and lead time over the replenishment period.
safety stock = Z x sqrt(lead time x demand variance + demand^2 x lead time variance)
The Z factor rises steeply near the top of the service level range, which is why the last few percent of availability is disproportionately expensive.
FAQ
Why not just hold two weeks of cover?
Because a flat rule ignores variability. Two weeks is generous for a steady item with a reliable supplier and inadequate for a volatile one, and the same rule applied to both wastes money and causes stockouts simultaneously.
Why is a 99% service level so expensive?
Because the safety factor rises steeply at the top of the distribution. Moving from 95% to 99% can roughly double safety stock, which is worth paying for on critical items and rarely worth it across a whole catalogue.
Which variability matters more?
Usually lead time. It enters the calculation multiplied by average demand, so an unreliable supplier drives more buffer than variable demand does — and negotiating reliability is often cheaper than financing the stock.
How we compare
| Feature | Online Tool Store | A spreadsheet | An advisor consultation |
|---|---|---|---|
| Both variability sources | ✓ | Demand only | ✓ |
| Service level choice | ✓ | ✗ | ✓ |
| No sign-up | ✓ | ✗ | ✗ |
| Nothing uploaded | ✓ | ✗ | ✗ |
Inventory Buffer Calculator shows which variability is driving your buffer — usually the supplier's, which is negotiable in a way demand is not.