How to Set Low-Stock Thresholds That Actually Work
By Ty Fisher, founder of Fisher Software
A low-stock threshold is the inventory level that tells you an item needs attention before it reaches zero. A useful threshold is based on how quickly the item sells, how long replenishment takes, and how much buffer the business needs. It should create enough time to act without forcing the business to carry unnecessary stock.
In short: A low-stock threshold should be based on average daily demand, supplier lead time, and safety stock—not one percentage used for every SKU. A practical starting point is average daily demand multiplied by lead time, plus the safety stock you want available for delays or demand spikes.
What is the difference between low stock and a reorder point?
Low stock is a warning condition. A reorder point is the inventory level at which you normally place the next order. Many small businesses use the same number for both, but separating the ideas can be helpful.
For example, a reorder point may be 20 units because that is when an order should be placed. A low-stock warning may begin at 24 units so someone has time to review sales, open purchase orders, supplier timing, and any stock already moving between locations.
How do you calculate a practical starting threshold?
Starting reorder point = average daily demand × supplier lead time + safety stock
Start with recent demand and real supplier timing. If an item sells four units per day and the supplier normally takes five days, expected lead-time demand is 20 units. Add the safety stock you want to protect against delays or demand spikes.
If the business keeps eight units of safety stock, the starting reorder point is 28 units. That number is not permanent. It is a baseline that should change when sales pace or supplier performance changes.
How much sales history should you use?
Use enough history to represent normal demand, but do not let old data hide a recent change. Thirty to ninety days is often a useful starting window for a stable item. Seasonal products need a comparison with the same period from a prior season when that information exists.
Averages can also hide spikes. If a product usually sells two units a day but regularly sells ten on weekends, the business needs a threshold that survives the busy period. Review the pattern, not only the average.
How should supplier lead time affect the threshold?
Supplier lead time is the number of days between placing the order and having usable inventory available. Use actual receiving history when possible, not only the lead time printed on a supplier sheet.
If a supplier says five days but recent orders took seven, the threshold should reflect the seven-day reality until service improves. A business that ignores changing lead time often discovers the problem only after the shelf is empty.
- Measure from order placement to usable receipt.
- Include weekends or processing days when they affect delivery.
- Watch partial shipments and backorders separately.
- Update the threshold when the supplier becomes faster or slower.
When should you add safety stock?
Safety stock is useful when demand or supplier timing is uncertain. It is not a requirement for every product. A slow item with a reliable supplier may need little or no buffer, while a fast seller with unpredictable deliveries may need several days of protection.
The cost of a stockout matters too. A product that customers can easily replace may need less protection. A part that stops a repair job or a key item that drives repeat traffic may justify a larger buffer.
Why should different products have different thresholds?
One threshold for every SKU is easy to set but rarely makes sense. Products move at different speeds, suppliers have different lead times, and the cost of running out is not the same for every item.
Group items by business impact. Fast sellers and critical items deserve closer review. Slow or expensive products may need smaller buffers so cash is not trapped on the shelf.
- Fast sellers: review often and allow more lead-time protection.
- Slow sellers: use smaller buffers and confirm demand before reordering.
- Long-lead items: reorder earlier even if daily demand is modest.
- Seasonal items: adjust thresholds before and after the selling season.
- High-cost items: balance stockout risk against cash tied up in inventory.
How often should low-stock thresholds be reviewed?
Review them whenever the facts change. A threshold can become wrong even when the formula was correct on the day it was created.
A monthly review works for many small businesses. Fast-moving or seasonal products may need weekly attention. Focus on exceptions: repeated stockouts, repeated overstock, supplier delays, or products that keep triggering alerts without needing an order.
What should you check before placing the order?
A low-stock alert should start a decision, not make the entire decision automatically. Check whether an open purchase order already exists. Look for stock at another location. Confirm recent sales are real and not caused by a one-time event.
Then review the order quantity. Ordering just enough to cross the threshold can create frequent purchasing. Ordering too much can trap cash. Use pack size, minimum order quantity, storage space, and expected demand to choose the final quantity.