Free tool
Weeks of cover calculator: when each SKU runs out and when to reorder
By Andrew Simpson, founder of Canopy Inventory. Last updated 6th November 2026: new tool, replacing the earlier inventory calculator and inventory audit
Quick answer
Weeks of cover is how long your stock lasts at your current sales rate: units in stock divided by units sold per week. The stockout date is today plus stock divided by daily sales. Count back your lead time and safety stock days from the stockout date and you have the date to reorder by. Enter one SKU below to get all three, plus a suggested buy quantity.
Your SKU
One variant at a time, in units. Nothing you type leaves your browser.
Shopify's Available quantity, not On hand.
Net units sold in the days you pick below.
Reorder settings (optional)
Filled in with Canopy Inventory's starting defaults. Change them to match your supplier.
Order placed to stock sellable.
Extra days of sales to hold.
How long each order should last.
Buy in multiples of this.
0 if there is none.
Ordered but not yet received.
Enter units in stock and units sold to see weeks of cover, the stockout date, the reorder-by date and a suggested buy.
The formulas this calculator uses
These are the same rules Canopy Inventory uses, written out in full on how Canopy Inventory calculates.
Daily sales rate = units sold in the window / days in the window
Weeks of cover = units in stock / (daily sales rate x 7), shown to 1 decimal place
Stockout date = today + units in stock / daily sales rate
Reorder-by date = stockout date - (lead time days + safety stock days)
Days to cover = lead time + target cover + safety stock (all in days)
Suggested buy = days to cover x daily sales rate - (units in stock + units on order), never below 0, rounded up to the pack size, then raised to the minimum order (MOQ) if lower
- Stock with no sales in the window shows "no sales". No stock and no sales is 0 weeks.
- No sales means no stockout date. A date more than 730 days away is not shown.
- Lead time and safety stock do not move the stockout date. They move the reorder-by date.
- A buy is only suggested when stock would run out within lead time + safety stock + 70 days. "Order now" shows when a buy is suggested and the reorder-by date is today or has passed, or the SKU is out of stock.
- The MOQ only applies when the buy is above 0. Safety stock is in days, not units, as in the app.
Worked example
Example (made-up round numbers)
Daily rate = 60 / 30 = 2 a day. Weekly rate = 14 a week.
Weeks of cover = 120 / 14 = 8.6 weeks.
Stockout date = 120 / 2 = 60 days from today.
Reorder-by date = 60 - (30 + 14) = 16 days from today.
Days to cover = 30 + 60 + 14 = 104. Need = 104 x 2 - 120 = 88 units. Rounded up to packs of 12 = 96. Raised to the MOQ = 100 units.
Stock runs out in 60 days, which is within 30 + 14 + 70 = 114 days, so the buy is suggested. The reorder-by date is 16 days away, so it does not say "Order now" yet.
Using it to set a reorder cadence per SKU
Reorder cadence is how often a SKU needs a new order. The target cover setting decides it: each order is sized to last your lead time, then your target cover, plus safety stock. With 60 days of target cover, a steady seller needs an order roughly every 60 days. Run the calculator for your best sellers first, note each reorder-by date, and group SKUs from the same supplier whose dates fall close together into one order.
How to get the inputs from Shopify
- Units in stock: open the product variant in your Shopify admin, or the Inventory page, and use the Available quantity. On hand includes units already committed to unfulfilled orders.
- Units sold: in Analytics > Reports, open a sales by product variant report, set the date range to your window ending yesterday, and use net items sold.
- A shortcut:Shopify's "Inventory remaining per product" report estimates days of inventory remaining from the last 28 days of sales. Divide by 7 for weeks of cover.
- Lead time: the days from placing an order with your supplier to the stock being sellable. See how to calculate lead time.
How Canopy Inventory does it
Canopy Inventory is a read-only Shopify app, coming soon to the Shopify App Store. It does these sums for every SKU from your Shopify data: Shopify's available stock across your sellable locations, and units sold including units sold inside bundles, net of cancellations and refunds. It shows weeks of cover for a 7, 14, 30, 45, 60 or 90-day window and plans the stockout date, reorder-by date and buy quantity on 30 days of sales (or all your history if that is shorter).
Two differences from this manual tool: the app adds incoming purchase orders to the stockout date on their expected dates, and it shows the cash to buy at your Shopify cost per item. The Free plan covers your 50 most recently sold SKUs with shop-wide settings; Growth adds every SKU, incoming purchase orders entered by hand and settings per supplier and SKU. See pricing.
Weeks of cover for every SKU, without the spreadsheet
Canopy Inventory is coming soon to the Shopify App Store. One email the day it's live. Free for your 50 most recently sold SKUs.
Questions
What tool calculates reorder cadence per SKU from Shopify data?
For one SKU, this calculator does it: enter units in stock and units sold in a window, and it gives weeks of cover, a stockout date and a reorder-by date. Across a whole catalogue you can build the same sums in a spreadsheet from Shopify’s inventory and sales reports, or use an app. Canopy Inventory, a read-only Shopify app coming soon to the Shopify App Store, works them out for every SKU from your Shopify data.
How do I forecast when stock will run out?
Divide units in stock by units sold per day. 120 units selling 2 a day lasts 60 days, so the stockout date is 60 days from today. This is a simple run-rate forecast: it assumes you keep selling at the rate of your chosen window.
Which sales window should I use?
30 days suits most steady sellers. Use 60 or 90 days for slow sellers that do not sell every week, and 7 or 14 days for a product that is taking off. Avoid a window that includes a big promotion or days when the SKU was out of stock, because both distort the rate.
Why does the calculator say "no sales"?
There is stock but no units sold in the window, so there is no sales rate to divide by. Try a longer window. If the SKU has not sold in 90 days, it may be dead stock.
Does it include stock I have on order?
Units on order are taken off the suggested buy. They are not added to weeks of cover, and this manual tool does not move the stockout date for them, because it does not know when they arrive.
Is weeks of cover the same as weeks of supply?
Yes. Weeks of cover, weeks of supply, stock cover and weeks of stock all mean how long your stock lasts at your current sales rate.
Sources
- Shopify Help Center, Inventory states (available, on hand and committed). Checked 6th November 2026.
- Shopify Help Center, Inventory reports ("Inventory remaining per product" uses the last 28 days of sales). Checked 6th November 2026.
- Canopy Inventory's own rules: how Canopy Inventory calculates.