Worked example
You sell 20 units a day on average, 32 on your busiest day. Your supplier normally takes 5 days, 8 at worst.
(32 × 8) − (20 × 5) = 156 units of safety stock. Reorder when you hit 100 + 156 = 256 units.
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Safety stock calculator
Work out how much buffer stock to hold so a busy week or a late supplier doesn't leave you empty — using the two formulas inventory planners rely on.
Method 1 — Max vs. average (best for most small businesses)
Safety stock
156 units
Reorder point (incl. safety stock)
256 units
Method 2 — Service level (when you know demand variation)
Safety stock at 95%
23 units
Z-score used
1.65
Keep it from tying up cash
- Only hold high safety stock for items that stop sales or jobs.
- Recalculate each quarter and before peak season.
- Shorter, more reliable lead times reduce safety stock more than anything else.
Stop doing this math in a spreadsheet
StockSimple tracks stock, cost prices and stock value for you, emails you when items hit their reorder level, and scans barcodes with your phone. From $6.99/month, 14-day free trial, no card needed.
Try StockSimple freeFrequently asked questions
What is the safety stock formula?
The simplest formula is: (maximum daily usage × maximum lead time) − (average daily usage × average lead time). The statistical formula is: Z × standard deviation of daily demand × √lead time.
Which safety stock method should I use?
Use the max-vs-average method if you know your busiest day and slowest supplier delivery. Use the service-level method if you have enough sales history to calculate the standard deviation of daily demand.
What service level should I choose?
95% is a common starting point. Use 97.5–99% for items that stop work when they run out, and 90% for low-value or easily substituted items.
How is safety stock different from reorder point?
Safety stock is the buffer. The reorder point is when to order: average daily usage × lead time + safety stock.
Can I get alerts when stock hits this level?
Yes. Set the reorder point as a product's minimum in StockSimple and you get a daily low-stock email listing everything at or below it.
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