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Safety stock calculator formulas
The statistical method combines demand variance and lead-time variance, then applies the service factor you select. The average–maximum method subtracts average lead-time demand from maximum lead-time demand.
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Safety Stock Calculator
Calculate a whole-unit uncertainty buffer with an explicit statistical or average-maximum method—without turning it into a reorder-point recommendation.
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01 USE IT NOW02 NO ACCOUNT03 FIELD NOTES BELOW
WORKING INPUTS
Choose the buffer method.
LIVE RESULT
Safety stock
170 unitsCombined variability · 95% service level. This is an uncertainty buffer, not a reorder point.UNROUNDED BUFFER169.0747 units
WHOLE-UNIT SAFETY STOCK170 units
SELECTED METHODCombined variability · 95% service level
SERVICE FACTOR1.65
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THE BUFFER BETWEEN PLAN AND REALITY
Make uncertainty visible before it becomes a stockout.
Demand and supplier timing rarely repeat perfectly. A declared method turns that variability into a transparent buffer while leaving the reorder trigger as a separate decision.
WORKING VIEW
170 SAFETY-STOCK UNITSCOMBINED VARIABILITY
METHODselected uncertainty method, rounded up once to whole units
WORKING NOTE100/day average · 10 demand σ · 5-day average · 1-day lead-time σ · 95%
INPUTS → CLEAR OUTPUT
THE FIELD NOTES
Quick answer above. Better decisions below.
Use the result now, then read the practical notes for assumptions, examples, limitations, and the choices behind it.
COMBINED VARIABILITY170 SAFETY-STOCK UNITS
100/day average · 10 demand σ · 5-day average · 1-day lead-time σ · 95%
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Use consistent demand and lead-time data
Use observations for the same SKU, location, demand unit, and lead-time unit. Mixing weekly demand with daily lead time silently changes the result.
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Declare the service level
The statistical method exposes four common service-factor choices: 90%, 95%, 98%, and 99%. The selected target changes the buffer directly.
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Safety stock is not the reorder point
Safety stock is the uncertainty buffer only. A reorder point also incorporates expected demand during lead time and an inventory-position trigger.
THE UNCERTAINTY BUFFER IS CLEAR
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Safety stock calculator formulas
The statistical method combines demand variance and lead-time variance, then applies the service factor you select. The average–maximum method subtracts average lead-time demand from maximum lead-time demand.
Both methods calculate at full precision and round upward once to whole units. They are alternative planning models, not interchangeable truths.
Use consistent demand and lead-time data
Use observations for the same SKU, location, demand unit, and lead-time unit. Mixing weekly demand with daily lead time silently changes the result.
Exclude unusual periods only under a documented policy. A short or unrepresentative history can make averages, maximums, and standard deviations misleading.
Declare the service level
The statistical method exposes four common service-factor choices: 90%, 95%, 98%, and 99%. The selected target changes the buffer directly.
A higher service target is not automatically better. Holding cost, product value, stockout impact, shelf life, and supplier flexibility belong in the business decision.
Safety stock is not the reorder point
Safety stock is the uncertainty buffer only. A reorder point also incorporates expected demand during lead time and an inventory-position trigger.
The calculator does not forecast demand, recommend purchase timing or quantity, optimize a service level, or guarantee that stockouts will not occur.
Questions, answered.
How do I calculate safety stock with demand and lead-time variability?
Use a declared service factor multiplied by the square root of average lead time times demand variance plus average daily demand squared times lead-time variance, then round upward once to whole units.
What is the average-maximum safety stock method?
Multiply maximum daily demand by maximum lead time, subtract average daily demand multiplied by average lead time, and round the nonnegative result upward to whole units.
Is safety stock the same as reorder point?
No. Safety stock is an uncertainty buffer. A reorder point also considers expected demand during lead time and the inventory position that triggers replenishment.
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