Stockouts cost you sales and damage customer trust. This step-by-step guide explains how to calculate the right reorder point for each product, set automatic alerts, and keep your inventory replenished before it becomes a crisis.
It's a Tuesday morning and your best-selling product just sold out. A customer placed a large order overnight, your warehouse team confirms there's nothing left on the shelf, and your supplier needs eight days to deliver. You start doing the math: eight days of lost sales, a handful of frustrated customers who'll probably shop elsewhere, and a team spending the morning fielding complaint emails instead of doing real work.
This isn't bad luck. It's a system problem—specifically, the absence of a reorder point. Without one, you're managing inventory by gut feeling, and gut feelings don't scale.
The good news is that fixing this is not complicated. You don't need a logistics degree or an enterprise ERP costing six figures. You need a formula, a process, and a tool that enforces the discipline automatically. This guide walks you through exactly that.
What a Reorder Point Actually Is
A reorder point (ROP) is the inventory level that triggers a new purchase order. When stock drops to that number, your team (or your software) immediately initiates replenishment. You're not waiting until the shelf is empty—you're acting while you still have buffer stock to survive the supplier's lead time.
The classic formula is:
ROP = (Average Daily Sales × Lead Time in Days) + Safety Stock
That's it. Three variables. Let's break each one down so you can calculate a real number for each SKU you carry.
How to Calculate Average Daily Sales
Pull your sales data for the last 30 to 90 days and divide total units sold by the number of days in that period. Use a window that reflects your current reality—if your business is seasonal, use the most recent comparable season, not an average that includes slow months.
Handling Demand Spikes
If your sales data is erratic—say, you sell 5 units most days but occasionally sell 50 because a retailer places a bulk order—a straight average will mislead you. In that case:
- Segment your demand. Calculate a baseline daily rate for regular orders and handle large accounts separately with dedicated stock or custom reorder logic.
- Use a weighted average. Give more weight to recent weeks if demand is trending up or down.
- Flag high-variance SKUs. These need wider safety stock buffers, which we'll cover next.
The goal is a number you can defend. If someone asks why you reorder at 200 units, you should be able to say: "We sell 25 units a day on average, lead time is six days, and we keep three days of safety stock. That's 150 + 75 = 225, rounded down to 200."
Understanding Lead Time (and Why You Should Pad It)
Lead time is the number of days between placing a purchase order and receiving usable stock. "Usable" is the key word—count the time until products are on your shelf and ready to sell, not just when the truck arrives.
Talk to your suppliers and pull your own purchase order history. If your supplier says five days but your records show an average of seven, use seven. Build your ROP on reality, not promises.
Add a safety buffer for unreliable suppliers. If a supplier is late 30% of the time, treat their lead time as their average actual delivery time plus one standard deviation. You're not punishing them; you're protecting your customers.
Here's a quick reference for common lead time scenarios:
| Supplier Type | Quoted Lead Time | Recommended Planning Lead Time |
|---|---|---|
| Local, highly reliable | 2 days | 2–3 days |
| Domestic, occasional delays | 5 days | 7 days |
| International, stable | 14 days | 18 days |
| International, variable | 21 days | 28+ days |
Setting Safety Stock: Your Insurance Policy
Safety stock is the inventory you hold above and beyond what the formula says you need. It exists to absorb two types of uncertainty: demand spikes and supplier delays.
A simple approach: multiply your average daily sales by the number of days of coverage you want. If you sell 25 units a day and want three days of cushion, your safety stock is 75 units.
A more precise approach uses this formula:
Safety Stock = Z × σ(demand) × √(Lead Time)
Where Z is a service level factor (1.65 for 95% service level, 2.05 for 98%), and σ(demand) is the standard deviation of your daily sales. This is the method to use once you've got clean data and want to optimize capital—holding too much safety stock ties up cash unnecessarily.
For most SMBs starting out, two to three days of average sales as safety stock is a practical, defensible starting point.
Turning the Math Into Alerts That Actually Work
A reorder point is useless if it lives in a spreadsheet nobody checks. The number needs to trigger an action automatically, ideally without requiring anyone to remember to look.
Here's how to operationalize it:
- Set system alerts at the ROP level so the right person gets notified the moment stock crosses the threshold.
- Assign ownership. One person—not "the team"—is responsible for acting on each alert within 24 hours.
- Define the response. When the alert fires, the action should be pre-decided: send the standing purchase order to supplier X for Y units at Z price. Remove decision fatigue from the process.
- Review ROPs quarterly. Demand changes, suppliers change, your product mix changes. A ROP set six months ago might be dangerously low today.
- Don't set alerts only at the ROP. Add a secondary "warning" alert at 125–150% of your ROP to give yourself early visibility if you're burning through inventory faster than usual.
A Real-World Example: How One Retailer Fixed a Chronic Stockout Problem
Consider a small electronics accessories retailer selling phone cases online. They had a fast-moving SKU—a case for a popular phone model—that kept stocking out. Their supplier in Shenzhen had a 14-day lead time, but they were reordering only when stock hit 50 units, based on nothing more than habit.
After calculating properly: 30 units/day average sales × 18 days planning lead time + 60 units safety stock = 600-unit reorder point. They had been triggering reorders at 550 units too late.
Once they corrected the ROP and set automated alerts in their inventory system, stockouts on that SKU dropped to zero over the following quarter. More importantly, the buying team stopped making reactive emergency orders—which had been costing them 15–20% more per unit in expedited shipping.
How Pleelo Solves This
Pleelo's inventory module lets you set reorder points at the SKU level, configure automated alerts by team member or role, and track lead times per supplier—so the formula isn't just a number in a spreadsheet, it's a live trigger in your workflow. When stock hits your threshold, the right person gets notified and can convert the alert into a purchase order in a few clicks.
"Before Pleelo, we were reordering based on vibes. Now the system tells us exactly when to buy and we haven't had a stockout in four months. The setup took less than an afternoon." — Carlos M., Operations Manager, mid-size wholesale distributor
The system also logs your reorder history, so you can audit past decisions and tighten your formulas over time as you accumulate better data.
Get Started Today
Stop managing inventory by instinct. Set your reorder points once, let the system do the watching, and redirect your team's energy toward growth instead of firefighting.
