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Safety Stock Calculator: Avoid Stockouts

Work out how much extra stock to hold against late deliveries and demand spikes, with the simple max and average method or a target service level.

Safety stock

600units

Reorder point

1,200units

Safety stock = max daily usage × max lead time − average daily usage × average lead time

Reorder point = average daily usage × average lead time + safety stock

How to calculate safety stock

Safety stock is the extra inventory you keep so that a slow delivery or a busy week does not leave the shelf empty. Too little and you lose sales; too much and cash sits in the warehouse. This calculator gives two standard ways to set it, plus the reorder point.

How to calculate safety stock

Max and average method: (maximum daily usage × maximum lead time) − (average daily usage × average lead time). With 60 a day at most over 20 days, against 40 a day over 15 days on average: 1,200 − 600 = 600 units.

Service level method: Z × σ demand × √lead time. At a 95% service level (Z = 1.645), a daily demand standard deviation of 12 and a 15 day lead time: 1.645 × 12 × √15 ≈ 77 units. Add lead time variation if your supplier is unreliable.

Service level and Z

Service levelZ
90%1.28
95%1.645
98%2.05
99%2.33
99.9%3.09

Reorder point

Reorder point = average daily usage × average lead time + safety stock. Plan the lead time with the lead time calculator.

Copy the result, or save it as a PDF to attach to an email or a purchase file. Nothing you type leaves your browser.

Features

  • Max and average method
  • Service level with Z score
  • Demand and lead time variation
  • Reorder point
  • 85% to 99.9% service levels
  • Copy or PDF

Frequently asked questions

What is a good service level?

Many businesses use 95% for most items and 98 to 99% for best sellers or critical parts. Higher levels cost more stock.

Which safety stock formula should I use?

The max and average method is quick when you lack data. With daily sales history, the service level method is more precise.

How often should I recalculate safety stock?

At least every quarter, and whenever demand, the supplier or the lead time changes.

Is the calculator free?

Yes. No sign up. It runs in your browser, and you can copy the result or save it as a PDF.

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