Free Tool
Free Inventory Calculator
Enter your stock level and sales rate to instantly see your weeks of cover, reorder point and run-out date. No signup required.
What does this calculator do?
This inventory calculator tells you how many weeks of stock you have left, when you need to reorder based on your supplier lead time, and exactly when you'll run out if you don't act. It's the same calculation Canopy runs automatically for every SKU in your Shopify store — updated every day.
Enter your stock details
The number of units you currently have available to sell.
Your average units sold per week. Use a 12-week rolling average for accuracy.
Total days from placing an order to receiving stock. Default 70 days reflects China manufacturing + sea freight.
Extra days of stock to hold as a buffer against delays or demand spikes. 14 days is a good starting point.
Enter your current stock level and weekly sales above to see your results.
Understanding your inventory metrics
Weeks of cover
Your current stock divided by weekly demand. Less than 4 weeks is critical — especially if your supplier is 70+ days away. 8–16 weeks is the healthy range for most Shopify brands sourcing from overseas.
Reorder point
The stock level at which you must place an order. It includes your lead time demand (daily sales × lead time days) plus your safety stock buffer. When stock hits this number, your next order should already be on its way.
Run-out date
The date you will have zero units left if no new stock arrives. This is your hard deadline — your reorder must arrive before this date. Factor in 7–14 days of safety stock on top.
Recommended reorder quantity
A 60-day replenishment batch — enough stock to cover two months of sales. This is a starting point; your actual order quantity should account for minimum order quantities (MOQs), seasonal demand and cash flow.
Canopy calculates this automatically for all your SKUs
Stop running this calculation manually in spreadsheets. Canopy connects to Shopify and updates every SKU's weeks of cover, reorder point and run-out date every single day.
Inventory calculator — frequently asked questions
Weeks of cover (also called stock cover or days of cover) is the number of weeks your current stock will last at your current rate of sales. It is calculated by dividing your current stock level by your average weekly sales. For example, if you have 500 units and sell 50 per week, you have 10 weeks of cover. Knowing your weeks of cover is essential for planning purchase orders — especially when your supplier lead time is 8–12 weeks or more.
Most ecommerce brands aim for 8–16 weeks of cover for fast-moving SKUs, adjusted for supplier lead time. If you source from China with a 70-day production lead time plus 30 days sea freight, you need at least 14–15 weeks of cover before you can place an order and receive stock. Brands with long lead times should carry more cover; brands with local suppliers can manage on less. The key is that your weeks of cover never falls below your combined lead time plus safety buffer.
The reorder point is calculated as: (daily demand × lead time in days) + safety stock. For example, if you sell 10 units per day, your supplier takes 70 days to deliver, and you want 14 days of safety stock, your reorder point is (10 × 70) + (10 × 14) = 840 units. When your stock hits 840 units, you should be placing your next order. Canopy calculates this automatically for every SKU.
To calculate your run-out date, divide your current stock by your average daily sales rate to get the number of days remaining, then add that number to today's date. For example, if you have 300 units and sell 15 per day, you will run out in 20 days. This calculator does that maths for you automatically. Canopy updates these figures daily for every SKU in your Shopify store.
Safety stock is a buffer held to absorb demand spikes or supply delays — it is stock you hold but plan never to sell below. The reorder point is the stock level at which you trigger a purchase order. The reorder point includes your safety stock: ROP = (daily demand × lead time) + safety stock. Safety stock sits at the bottom of the stack; the reorder point is the trigger level above it.
Related tools and guides
Automate this calculation across your entire catalogue
Canopy tracks weeks of cover, reorder points and run-out dates for every SKU in your Shopify store — updated daily, automatically.