Free Days of Stock Calculator
Know your runout date before it's too late
Enter your current stock quantity and average daily sales to instantly see how many days of inventory you have left and the estimated date you'll run out — so you can reorder on time.
What Is a Days of Stock Calculator?
A Days of Stock Calculator tells you exactly how long your current inventory will last at your current rate of sales. Simply enter the units you have in stock and how many you sell per day, and the tool shows the number of days remaining and the estimated runout date. It also flags urgent situations (less than 3 days) and low stock (under 7 days), so you can act before you run out and lose sales.
How to Calculate Days of Stock Remaining
Step 1 — Enter Current Stock Quantity
Type the number of units you currently have in stock for the product you want to check.
Step 2 — Enter Average Daily Sales
Enter how many units you sell per day on average. If you sell weekly, divide by 7. For monthly sales, divide by 30.
Step 3 — See Days Left & Runout Date
The tool shows how many days your current stock will last and the estimated date you will run out — so you know when to place your next reorder.
Who Uses This Days of Stock Calculator?
Shop & Store Managers
Check if you have enough stock to last until the next supplier delivery without running out mid-period.
Pharmacy Owners
Know exactly how many days a medicine batch will last based on prescription rates, to reorder before expiry risk.
Warehouse Teams
Prioritise which SKUs need urgent replenishment by comparing days of stock across all products.
E-commerce Sellers
Prevent out-of-stock notices on your listings by tracking how long each product will last at current sell-through.
Frequently Asked Questions
What is days of stock (DOS)?
Days of Stock (also called Days of Supply) is the number of days your current inventory will last at your current rate of sales. Formula: DOS = Current Stock ÷ Average Daily Sales.
How do I calculate average daily sales?
Total units sold in a period ÷ number of days in that period. Example: 300 units sold in 30 days = 10 units/day average.
How does Days of Stock differ from Reorder Point?
Days of Stock tells you how long your current inventory will last. Reorder Point tells you the quantity level at which you should order. Use both together: DOS to plan ahead, ROP to set alerts.
What should I do when I have too few days of stock?
If your DOS is less than your supplier's lead time, you should order immediately. Use our Reorder Point Calculator to set the right trigger level so you're never in this situation again.
Can I use this for multiple products?
Yes. Run the calculation separately for each product. For managing many SKUs at once, our inventory management software tracks days of stock for all products automatically.
Is this days of stock calculator free?
Yes, completely free. No account or login required.