How to Calculate Days of Cover for BigCommerce Products

• November 5, 2026
• Nadeem Shaikh
• no comments

Days of cover tells you how many days your current stock will last if sales keep their recent pace. To work it out, divide the units you have on hand by your average daily sales, usually from the last 30 days. A product with 20 units on hand that sold 60 units in 30 days has 10 days of cover.

That one number makes it much easier to see which products could run out first. In this guide we walk through the formula, a worked example, the tricky edge cases, a spreadsheet method you can use today, and a free app that does the math for you.

What is days of cover?

Days of cover (also called days of inventory cover or days of stock) is a simple estimate: “At the speed this product has been selling, how long will what I have last?”

It is not a forecast and it does not know about next month’s holiday rush. It looks back at recent sales and forward at your current stock. That makes it easy to understand and easy to check, which is exactly why many small store owners like it.

Why it beats looking at stock counts alone

A stock count of 50 sounds healthy. But 50 units of a product that sells 10 a day lasts five days, while 50 units of a product that sells one a week lasts almost a year. Days of cover puts every product on the same scale (days), so you can compare a fast seller and a slow seller side by side.

The days of cover formula

Here it is in plain terms:

Days of cover = stock on hand ÷ average daily sales

And average daily sales is:

Average daily sales = units sold in the period ÷ number of days in the period

Most people use a 30-day period. It is recent enough to reflect what is happening now, but long enough that one busy afternoon does not throw the number off.

A worked example (made-up numbers)

The numbers below are an example only, not real store data.

Say you sell three products:

Product	On hand	Units sold (last 30 days)	Avg daily sales	Days of cover
Ceramic mug	20	60	2.0	10
Wool scarf	45	30	1.0	45
Gift card holder	12	0	0	blank

Step by step for the mug:

1. Units sold in 30 days: 60
2. Average daily sales: 60 ÷ 30 = 2 per day
3. Days of cover: 20 ÷ 2 = 10 days

The scarf has more stock relative to its sales, so it has 45 days of cover. The mug is the one to look at first.

The edge case: no recent sales

Look at the gift card holder. It sold nothing in 30 days, so average daily sales is zero, and dividing by zero does not give a real answer. Some tools show “infinite” days of cover, which can be misleading. It makes a product that nobody is buying look like it has endless healthy stock.

A cleaner approach is to leave days of cover blank when there are no recent sales. A blank is honest: “There is not enough recent sales data to estimate this.” It also nudges you to ask a different question about that product, such as whether it needs a price change or a better product page.

Other things to keep in mind

• New products: If a product launched 10 days ago, a 30-day average understates its pace. Treat the number with care.
• Stockouts: If a product was out of stock for part of the month, it could not sell during those days, so the average looks lower than real demand.
• Seasonality: A 30-day window before a big holiday will not reflect the holiday itself. Compare with 60 and 90-day sales to get a feel for the trend.

How to calculate days of cover in a spreadsheet

You can do this without any app:

1. Export your orders for the last 30 days from your BigCommerce admin.
2. In a spreadsheet, total the units sold for each product or SKU (a pivot table works well).
3. Add a column for current stock on hand from your product export.
4. Add a column for average daily sales: =units_sold/30.
5. Add a column for days of cover: =IF(units_sold=0,"",on_hand/(units_sold/30)).
6. Sort by days of cover, lowest first.

This works fine, but you have to repeat it every time you want fresh numbers, and it gets slow with a big catalog.

What is a “good” number of days of cover?

There is no single right answer, because it depends on how long your supplier takes to deliver (lead time) and how much buffer you like to keep (safety stock).

A simple way to think about it:

• If your supplier usually takes 10 days to deliver, a product with 8 days of cover may run out before new stock arrives.
• If you want a buffer of about a week on top of that, you might start paying attention once a product drops below roughly 17 days (10 days lead time plus 7 days buffer).

These are example numbers. Your own lead times and comfort level decide the threshold. The data shows you where each product stands; you make the call.

A free way to see days of cover for every product

If you would rather not rebuild the spreadsheet every week, Runway is a free, read-only BigCommerce app from GrtLabs that shows this for you. For each product it shows units sold in the last 30, 60 and 90 days, stock on hand, and days of cover, calculated the same way as above (on-hand stock divided by average daily sales from the last 30 days). Products that run out soonest sit at the top, products with no recent sales show a blank instead of an endless number, and you can download the list as a CSV. You can find it on the BigCommerce App Marketplace.

Runway only reads orders, products and inventory. It does not create purchase orders, email suppliers or change your stock. It gives you the numbers; you decide what to order.

If you need something more custom for your store, our team also builds BigCommerce apps and integrations.

Quick recap

• Days of cover = stock on hand ÷ average daily sales.
• Use the last 30 days for a recent, steady average.
• Leave it blank when there were no sales, rather than calling it infinite.
• Compare against your supplier lead time plus a buffer.
• Check 60 and 90-day sales to spot trends.

FAQ

What is days of cover in inventory?

Days of cover is an estimate of how many days your current stock will last at your recent sales pace. It is calculated by dividing stock on hand by average daily sales.

How do I calculate days of cover?

Divide units sold in a period (often 30 days) by the number of days to get average daily sales. Then divide stock on hand by that number. For example, 20 on hand ÷ (60 sold ÷ 30 days) = 10 days of cover.

What if a product has no sales in the last 30 days?

Average daily sales is zero, so the formula cannot give a real answer. It is clearer to leave days of cover blank than to show an infinite number.

What is a good days of cover number?

It depends on your supplier lead time and the buffer you want to keep. Many store owners compare days of cover with lead time plus a few extra days of safety stock.

Does BigCommerce show days of cover?

You can calculate it from your order and product exports in a spreadsheet. Runway, a free read-only BigCommerce app from GrtLabs, shows days of cover for each product along with units sold over 30, 60 and 90 days.