HesapHanem

Safety Stock Calculator

Enter maximum and average daily usage and lead times to find the safety stock.

How it is calculated

This is the max-minus-average method for safety stock. Worst-case demand during replenishment is max daily usage × max lead time, normal demand is average daily usage × average lead time, and safety stock = worst case − normal. Usage is in units per day and lead time in days. The maximum daily usage must not be below the average daily usage, and the maximum lead time must not be below the average lead time; otherwise no result is shown, and when they are equal the safety stock is 0. All four values must be zero or more and results are rounded to whole units. The method stacks the worst demand on top of the worst delay, so it is conservative compared with statistical methods that use a service level and the standard deviation.

Worked example

A product sells 40 units a day on average, peaks at 60 a day, usually arrives in 10 days, and in the worst case takes 14 days. Worst-case demand during the wait: 60 × 14 = 840 units. Normal demand: 40 × 10 = 400 units. Safety stock: 840 − 400 = 440 units. A reorder point would then be the normal demand plus this buffer, 400 + 440 = 840, so you reorder when 840 units are left.

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Common mistakes

  • Using the longest delay seen once in several years as the maximum lead time. One extreme event inflates the buffer, so use a worst case you would plan around.
  • Entering the maximums lower than the averages, such as a maximum usage of 30 against an average of 40. The inputs are inconsistent and the tool shows no result; the maximum must be at least the average.
  • Mixing time units, such as weekly usage with lead time in days. Daily usage and lead time in days must share the same base.
  • Treating the result as the order quantity. It is only the buffer; the normal demand during the lead time and your reorder size are separate decisions.
  • Using the same stock level for items with very different demand patterns. Each product needs its own maximum and average figures, because a steady item may need little buffer.

About this calculator

Safety stock is the extra inventory a business holds beyond expected demand to guard against running out when either demand spikes or a supplier's lead time runs long. The classic method compares the worst realistic case to the average case: it multiplies maximum daily usage by maximum lead time, then subtracts average daily usage multiplied by average lead time. The gap between those two figures is the buffer needed to survive the difference between a normal cycle and a bad one.

Retailers, manufacturers, and distributors use this figure to set reorder points and avoid stockouts without tying up excess cash in inventory that just sits on shelves. Too little safety stock means lost sales and unhappy customers when a shipment is delayed; too much ties up working capital and increases holding costs. With your maximum and average daily usage and your maximum and average lead times entered, the tool computes the buffer level that balances those two risks.

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