Accounting Share · Inventory & purchasing
Safety Stock Calculator
Estimate statistical safety stock when daily demand variation is independent and lead time is constant. A z-score is supplied directly rather than silently selected.
The interactive calculator requires JavaScript. The formula and worked example below remain available.
01 / Enter your figures
Make the numbers yours.
Use one currency and consistent time periods. Amounts are shown in your input currency units; no currency conversion is performed.
02 / See the working
Your calculation
Enter your figures, then choose Calculate. Or load the worked example.
03 / Understand the method
Formula and method
Safety stock = z × Daily demand standard deviation × √Lead time
Estimate statistical safety stock when daily demand variation is independent and lead time is constant. A z-score is supplied directly rather than silently selected.
How to use this calculator
- Collect the figures for the same entity, currency and reporting period.
- Enter each input using its label and unit. For percentages, enter 15 to mean 15%.
- Choose Calculate, inspect the breakdown and compare the result with your assumptions.
- Change one input to explore a scenario. Recalculate after edits; display rounding does not round the underlying calculation.
Inputs at a glance
- Service factor (z-score): A nonnegative numeric input in the units specified by the label.
- Daily demand standard deviation: A nonnegative numeric input in the units specified by the label.
- Constant lead time in days: A nonnegative numeric input in the units specified by the label.
Worked example
Follow one calculation.
- Service factor (z-score)
- 1.645
- Daily demand standard deviation
- 20
- Constant lead time in days
- 9
- Calculated result
- 98.7 units
Load this example in the interactive form to inspect the intermediate amounts.
Assumptions and interpretation
The normal-demand approximation is not appropriate for every item. Variable lead time, correlated demand and service-level definitions require different models.
The output is a model based on the figures entered. Check source records and use the accounting or contractual definitions relevant to your task before relying on a result.
Questions about this tool
What does the safety stock calculation measure?
Estimate statistical safety stock when daily demand variation is independent and lead time is constant. A z-score is supplied directly rather than silently selected.
Which assumptions can change the result?
The normal-demand approximation is not appropriate for every item. Variable lead time, correlated demand and service-level definitions require different models.
Why can displayed totals differ slightly from my spreadsheet?
Calculations use the unrounded input values. Only the display is rounded. Use four or six decimal places to inspect small differences, and check the timing, sign conventions and rounding policy in your spreadsheet.
Reference and further learning
Inventory reporting reference: IAS 2. These original learning examples apply the displayed formula; the reference does not certify or endorse this calculator.
Look up an accounting term · Practise with accounting questions
Formula and worked example checked 4 November 2026. Calculations run in your browser without sending the entered figures to Accounting Share. Report a calculation issue with the tool name, example inputs and expected result; avoid sharing confidential records.
