The Stockout Prevention Playbook for WooCommerce Stores
Every WooCommerce store owner knows the feeling. An order comes in. You check your inventory. It's empty. The supplier is two weeks out. You've lost that sale — and possibly the customer.
Stockouts aren't a bad luck problem. They're a math problem. And math problems have solutions.
This playbook walks you through exactly how stockouts happen, the reorder point formula WooCommerce stores use to prevent them, and the tool that does the calculation for you automatically.
How Stockouts Actually Happen
Most stockouts follow one of three patterns:
1. You didn't know you were running low.
Your stock count looked fine. You didn't realize you'd been selling 5 units a day when you thought you had 3 weeks of supply left.
2. You knew, but you didn't reorder in time.
You saw the low stock warning and planned to order "tomorrow." Tomorrow came, the order didn't, and you ran out.
3. Demand spike.
A product went viral, a Facebook ad hit, or seasonal demand kicked in faster than expected. Your reorder point was based on normal sales — not this week's sales.
The fix for all three patterns is the same: stop running inventory by gut instinct and start running it by math.
The Metric That Actually Matters: Days of Stock
Before you can prevent stockouts, you need to know one number: how many days of inventory do you have left?
Days of Stock Formula
Where sales velocity = your average units sold per day.
Example
You have 60 units of a product in stock. Over the last 30 days, you've sold 90 units. That's 3 units per day.
60 ÷ 3 = 20 days of stock
At your current sales rate, you'll run out in 20 days. If your supplier lead time is 7 days, you need to reorder when you hit 21 days of stock remaining — which means when you have 21 × 3 = 63 units left.
Wait. You only have 60.
That means you should have already reordered.
This is where most WooCommerce stores get caught. They look at the raw stock number and think "we're fine." They don't convert it to days — and when they do, they realize they're closer to zero than they thought.
The Reorder Point Formula: When to Reorder
The reorder point is the stock level at which you place a new order. It's calculated to ensure new inventory arrives before you run out.
Reorder Point Formula
Average daily sales = your typical units sold per day (use last 30 days, not last year)
Lead time = days from order placement to stock arriving in your warehouse
Safety stock = buffer for demand spikes and supplier delays
Example
Daily sales: 3 units
Supplier lead time: 7 days
Safety stock: 10 units
Reorder Point = (3 × 7) + 10 = 31 units
When your stock falls to 31 units, you place an order. New stock arrives 7 days later. You use the last 31 units while waiting. New stock arrives. You stay in stock.
This is the system. It works. Here's the problem: almost no small WooCommerce store actually does this.
Why Most WooCommerce Stores Don't Reorder in Time
The Four Most Common Mistakes
- They calculate by quantity, not by days. Looking at "I have 50 units" tells you nothing about whether 50 is enough. Enough for 3 days? 3 weeks? You can't know without the days calculation.
- They set WooCommerce low stock alerts on gut feel. Most store owners set the WooCommerce low stock threshold to a round number — "I'll get alerted at 10 units" — without knowing if 10 units is 2 days of stock or 2 weeks. It's arbitrary. For a fast-moving product, 10 units at 5/day = 2 days. For a slow mover, 10 units at 0.5/day = 20 days.
- They miss the lead time. If your supplier takes 14 days to deliver and your reorder point assumes 7, you'll hit zero before new stock arrives. The reorder point must be calculated against your actual lead time — not an estimate.
- They don't update reorder points when sales change. Seasonal products, successful ads, and new product launches all shift daily sales rates. A reorder point set in January may be dangerously wrong by March.
How to Actually Calculate Your Reorder Points (Step by Step)
Step-by-Step Guide
- Get your sales velocity per product. For each SKU, calculate your average daily sales over the last 30 days: (Total units sold in last 30 days) ÷ 30. Don't use last year. Use the last 30 days. Recent data beats historical data.
- Get your supplier lead time. Ask your supplier: "If I place an order today, how many days until it arrives at my warehouse?" That's your lead time. If it varies, use the maximum.
- Calculate your safety stock. Safety stock = (Maximum daily sales × Maximum lead time) − (Average daily sales × Average lead time).
- Calculate your reorder point. Reorder Point = (Average daily sales × Lead time) + Safety stock. When stock falls to this number, you order.
- Set it and track it. Put these numbers in a spreadsheet. Track them weekly. Update your reorder points when your sales velocity changes.
Full Calculation Example
Max daily sales (worst day in last 90 days): 8 units
Max lead time: 14 days
Average daily sales: 3 units
Average lead time: 7 days
Safety stock = (8 × 14) − (3 × 7) = 112 − 21 = 91 units
Reorder Point = (3 × 7) + 91 = 112 units
When stock falls to 112 units, you order. With 3 units/day selling through, you'll have ~21 days of stock on hand when the new order arrives. That's the buffer safety stock provides.
What WooCommerce Native Alerts Get Wrong
WooCommerce has built-in stock alerts. You can set a "low stock threshold" and receive an email when stock drops below it.
This is better than nothing. It's not enough.
The Critical Difference
WooCommerce alerts are quantity-based, not days-based. They tell you "you have 10 units left." They don't tell you "at your current sales rate of 4/day, you have 2.5 days of stock and your supplier takes 7 days to deliver."
That's the difference between a useful alert and a useless one.
You need an alert that says: "Order this product now — new stock won't arrive in time if you wait."
That's days-aware. That's what prevents stockouts.
WooCommerce Native Alerts
- Quantity-based ("10 units left")
- Static threshold — never adjusts
- Ignores your sales velocity
- Ignores supplier lead time
- No safety stock calculation
Days-of-Stock Alerts
- Days-based ("6 days of stock left")
- Updates with every sales cycle
- Driven by your actual sales rate
- Accounts for your lead time
- Includes safety stock buffer
Automate Your Reorder Points with DaysOfStock
Calculating days of stock, sales velocity, and reorder points for every SKU is a full-time job. For a store with 50 products, it's an afternoon every week. For 200 products, it becomes impossible.
DaysOfStock connects to your WooCommerce store and does this automatically:
- Pulls your 90-day sales history from WooCommerce
- Calculates days-of-stock for every product based on your actual sales velocity
- Sends you a daily email alert when any product crosses its reorder threshold
- Updates dynamically as your sales rate changes — no manual re-entry
You see one number per product: how many days until it runs out. When it crosses your reorder threshold, you get an email. You order. You stay in stock.
Plans start at $22/month. 7-day free trial, no credit card required.
Try DaysOfStock free for 7 days
Automatically track days of stock, calculate reorder points, and get alerts before you run out.
Start Free TrialThe Stockout Prevention Checklist
For Every Product in Your Catalog
- Calculate your average daily sales (last 30 days)
- Confirm your supplier's actual lead time
- Calculate safety stock using the formula above
- Calculate your reorder point = (daily sales × lead time) + safety stock
- Set a recurring calendar reminder to review reorder points monthly
- Switch from quantity-based alerts to days-of-stock-based alerts
- Track every stockout as an incident — identify what went wrong in the math
Most WooCommerce stores skip directly to step 7 without doing steps 1–6. They then wonder why they keep running out of stock.
Do the math. The stockouts will stop.