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Safety Stock Calculator

Model demand-only and combined variability buffers using demand deviation, lead-time deviation and a selected service factor.

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Variability buffer

Safety Stock Calculator

Model a statistical inventory buffer using demand variability, lead-time variability and an explicit service factor.

Combined variability buffer

111 units

Demand and lead-time variability combined through an independent-variance planning model.

Demand-only buffer

50 units

Combined buffer

111 units

Lead-time demand

420 units

Reorder point

531 units

Approximate service percentages assume a normal distribution and independent demand and lead-time variability. Validate the model against SKU history; it does not guarantee an in-stock rate.

About the Safety Stock Calculator

Safety Stock Calculator provides two transparent buffers: a demand-only result and a combined result that includes both demand and supplier lead-time variability.

Choose an explicit planning service factor and compare the resulting buffer with average lead-time demand and the calculated reorder point.

The displayed service percentages are normal-distribution approximations. Validate distribution assumptions and historical data quality instead of treating the result as a guaranteed in-stock rate.

Key features

  • Demand-only safety-stock model
  • Combined demand and lead-time variability
  • Selectable service factors
  • Average lead-time demand
  • Calculated reorder point
  • Local TXT export

How to use

  1. 1Calculate average daily demand and its standard deviation from a consistent history.
  2. 2Enter average supplier lead time and its standard deviation.
  3. 3Choose a planning service factor.
  4. 4Compare demand-only and combined buffers.
  5. 5Back-test the selected buffer against actual stockouts and carrying cost.

Examples

Variable demand and supplier timing
Input: 30 average daily units, demand deviation 8, 14-day lead time, lead deviation 2 and factor 1.65
Output: Combined safety stock and reorder point

Frequently asked questions

Which formula does the combined model use?
The service factor multiplies the square root of lead time × demand variance plus daily demand squared × lead-time variance.
What does the service factor mean?
It is a normal-distribution planning factor; the labels show approximate one-sided service percentages.
Does 95% guarantee 95% availability?
No. Real availability depends on data quality, distribution shape, review frequency and operational execution.
Can I use zero lead-time variability?
Yes. The combined result then reduces to the demand-only model.

Continue your workflow

Open a related tool to prepare your files or refine the finished result.