You can do everything right (track your usage, set a sensible reorder point) and still get caught out when something unexpected happens: a sudden rush of orders, or a supplier who ships two weeks late. Safety stock is the cushion that absorbs those surprises. It's the buffer between "running low" and "completely out."
What safety stock is
Safety stock is extra inventory you deliberately hold on top of what you expect to need, to cover the gap when reality doesn't match the plan. It's the difference between a reorder point that just covers your average usage and one that also survives a bad week. Without it, every estimate has to be perfect; with it, you have room to be wrong.
Why you need it
- Demand spikes: a feature, a viral post, or the holidays can blow past your usual usage.
- Supplier delays: lead times slip, especially in busy seasons.
- Estimate error: your usage rate is an average; some weeks run hot.
How much is enough?
More buffer is safer but ties up more cash, so the right amount is a balance. Two things push it up: how variable your demand and lead times are, and how costly a stockout would be (a lost signature product hurts more than a minor component). Two things push it down: steady demand, reliable suppliers, and the cash you'd rather not park on a shelf.
- Hold more buffer for unpredictable demand or unreliable lead times.
- Hold more for your critical, can't-run-out materials and best-sellers.
- Hold less for steady, easily-replaced supplies.
- Revisit it seasonally. Your buffer should grow heading into a busy stretch.
Safety stock is insurance: you hold a little extra so one bad week doesn't cost you a sale you can't fill.
Don't over-insure
The flip side is real: too much safety stock is just cash and space tied up for protection you rarely use. The goal isn't maximum buffer. It's enough to cover the surprises that actually happen to you, no more.
Build the buffer into your alerts
The simplest way to use safety stock is to fold it into your reorder point: set the trigger high enough that the buffer is still there when you reorder. From the Maker plan, Keepsel lets you set a low-stock limit on each material and alerts you when you reach it, so your buffer is something it watches for you, not a number you have to remember.