Stockout Date Calculator
Find the date you'll run out of stock, your weeks of supply and the last day to reorder, from your recent sales.
Your numbers
Your result · updates as you type
You'll run out of stock
In 35 days
35 days (5 weeks) of stock at 12 units a day. Reorder in 7 days to have stock back 7 days before you'd run out.
- Weeks of supply
- 5 weeks
- Reorder by
- in 7 days
- Reorder point
- 336 units
Place the order in 7 days. Stock at or below 336 units is your signal to reorder this product.
Breakdown
- Sales rate from your history
- 12 units a day
- Days the stock on hand lasts
- 35 days
- Stockout
- in 35 days
- Lead time + safety buffer
- 28 days
- Reorder by
- in 7 days
- Reorder point (units to cover lead time + buffer)
- 336 units
How the stockout date is worked out
Example
- Units in stock
- 420
- Units sold
- 360 in the last 30 days (12 a day)
- Supplier lead time
- 21 days
- Safety buffer
- 7 days
420 ÷ 12 = 35 days (5 weeks) of stock. 35 − 21 − 7 = reorder within 7 days. The reorder point is 12 × 28 = 336 units: once stock falls to that level, place the order.
If you already have stock on order, turn on I already have stock on order. If it lands before you sell out, it adds days of cover. If it lands after, the calculator shows your first stockout date and how long you'll be out.
Getting the sales rate right
- Use a recent, normal period. Leave out days you were out of stock, or your sales rate will look lower than real demand.
- Adjust for what's coming. Enter an expected change in sales for peak season, a launch or a bigger ad budget. The chart shows how fast a spike eats your cover.
- Work per variant when sizes or colors sell at different speeds. A product can have plenty of stock overall and still run out of its best-selling size.
- Lead time runs from order to sellable. Include production, freight, customs and the time it takes to receive and shelve stock.
Finding the numbers in Shopify and WooCommerce
- 01
Shopify
Go to Analytics → Reports and filter the category to Inventory. Shopify's inventory reports include days of inventory remaining, worked out from average daily sales over the last 28 days, which you can check against this calculator.
- 02
WooCommerce
Analytics → Stock lists stock levels and filters to low stock or out of stock. For units sold over a period, use Analytics → Products with a date range.
- 03
Set an alert
In WooCommerce, enter the reorder point as the product's Low stock threshold in the Inventory tab of the product data, so it shows as low stock at the right moment.
Questions people ask
How do I calculate weeks of supply?
Divide units on hand by units sold per week. 420 units selling 84 a week is 5 weeks of supply.
What's the difference between the stockout date and the reorder date?
The stockout date is when you sell the last unit. The reorder date is earlier by your supplier's lead time plus a safety buffer, so new stock arrives before you run out.
How big should my safety buffer be?
Big enough to cover how late your recent shipments ran plus a jump in sales. Use a bigger buffer for products you can't afford to run out of.
Should I count stock that's already on order?
Yes, if the order is confirmed and you know roughly when it lands. Turn on the incoming stock option so the calculator can check whether it arrives in time.
Does this work for each variant?
Yes, and it's more accurate that way. Run it for your best-selling sizes or colors separately, since they usually run out first.
Related tools
Want this builtinto your store?
I'm Emmanuel, a Shopify and WooCommerce developer. If this tool pointed at something you'd rather have fixed for you (a faster store, cleaner product data, a migration, a custom feature), send me a note.
Emmanuel Asika
Shopify & WooCommerce developer, Dublin
I build and fix online stores: new builds, migrations, speed, SEO and the custom bits apps can't do.
Last reviewed 30 September 2026.
Sources: Shopify Help: Inventory reports · WooCommerce: Stock report