Safety Stock: Meaning, Formula & Example

Vendors are late. Machines break down on the same day. Safety stock is how much extra you keep so that neither stops production.

Two ways to calculate it

1. Max-minus-average (most common in Indian plants)

Safety stock = (maximum daily usage × maximum lead time) − (average daily usage × average lead time)

2. Days of cover (simplest)

Safety stock = average daily usage × number of buffer days you want

Use method 1 when you have usage and delivery history. Use method 2 to get started.

Worked example

Bearing 6210 ZZ:

• Average daily usage: 8 nos, maximum 12 nos
• Average lead time: 10 days, worst case 14 days

Safety stock = (12 × 14) − (8 × 10) = 168 − 80 = 88 nos.

Using the days-of-cover method with 5 buffer days: 8 × 5 = 40 nos.

The first number protects you against the worst case you've seen. The second is a lighter buffer. Pick based on how critical the item is. (Illustrative figures.)

How much is too much

Safety stock is cash sitting on the shelf. Keep more for:

• Critical spares where a stockout stops a line
• Items with one vendor or long, unreliable delivery
• Imported items

Keep less for items available locally the same day.

Review safety stock at least twice a year. Usage changes when you add a machine or change a product mix, and a vendor who was reliable last year may not be this year.

Where it fits

Safety stock is added to lead-time demand to get the reorder level. It also sets the floor of min-max inventory.

How IndustryPrime handles it

You set minimum and maximum levels per item, with safety stock built into the minimum. IndustryPrime raises a reorder alert when stock falls below the minimum, and suggests the order quantity. Consumption history per item helps you revise levels as usage changes. See prevent stockouts.