Days of Cover: The Formula FBA Sellers Should Use

Days of cover tells you how many days of sales remain before a product’s stock runs out. For FBA wholesale buying it is the difference between ordering into a shortage and ordering into a glut.

Search results blur it with “days to cover,” a short-selling metric from stock trading. This guide separates the two, gives you the formula, and shows how to set a buy threshold from your own lead time.

Days of cover or days to cover: which one are you actually searching for?

Search “days of cover” and many results are about short selling, not inventory. Finance sites rank for “days to cover,” a short-interest metric: short interest divided by average daily share volume. It estimates how long short sellers would need to buy back borrowed shares. It has nothing to do with Amazon stock decisions.

The metric you want is days of cover: how many days the stock on a listing will last at the current sell-through rate. It tells you whether an ASIN is overstocked or running thin, so you can time your buy against your own lead time. We cover the full workflow in the million-dollar seller’s secret.

What is the days of cover formula?

Days of cover measures how long current inventory would last at the current sales rate. For a buying decision, the stock number is the total units available on the listing across all sellers, because that is the pool your units will compete with.

The sales rate usually comes from a recent window, such as 30 days, adjusted for seasonality and for any stockout gaps in that window. A stockout deflates the daily sales figure and makes days of cover look higher than it is, so check the window against the Keepa chart.

Six days means the listing runs dry inside a week. If the same ASIN held 300 units, you would get 20 days of cover, a very different read. Treat the result as a starting point for your own analysis. It is an estimate, not a promise of future sales.

How do you read days of cover on a Keepa chart?

Keepa does not print a days of cover number. It gives you the raw ingredients: sales rank history, offer count and price history. You estimate daily sales from how often the rank drops, then divide the stock you can see by that figure. A chart with steady rank and shrinking offer counts usually means demand is outrunning supply.

Is a low days of cover reading a buy signal or a trap?

A low reading means stock is thin relative to sales speed. That is the reason to look closer. Before you commit, read the offer-count line. If offers collapsed because other sellers lost the buy box, got gated or received an IP complaint, you may be buying their problem, not a shortage.

What does a high days of cover reading tell you?

A high reading means there is more stock than the ASIN can move quickly. Slow stock ties up cash and, on FBA, runs into storage fees and aged inventory surcharges. Wholesale sellers usually skip ASINs where the current offers already hold weeks of supply.

What days of cover should trigger a buy?

There is no universal number. In our own guide, products under about 15 days of cover are worth opening, and 20 days is worth monitoring. Those are starting points, not rules. Your real filter is your lead time.

Add up your own cycle: supplier invoice to shipment, transit, FBA check-in (often the slowest leg) and the time until you hold a buyable position. If that totals 21 days, a listing with 6 days of cover is likely to be refilled by other sellers before you arrive. In that case the question is not “is cover low today?” but “is cover falling week after week, and are fewer sellers staying in stock?”

FBM sellers skip FBA check-in, so their lead time is often shorter and they can act on a tighter signal. FBA sellers need to allow for the inbound window.

How does days of cover fit a wholesale sourcing workflow?

Wholesale sourcing starts with a supplier list of hundreds of lines, not one product. Use days of cover as your second-pass filter: run the list through ROI and profit first, then check cover on the survivors. A 40% ROI means little if the ASIN already holds months of stock.

Treat the checks as a sequence. ROI and profit decide whether a line is worth buying at all. Days of cover decides whether buying now makes sense. Competition checks, including how many sellers share the buy box, decide whether the buy box is realistic for you. If a product is moving fast and prices are already climbing, the window may be closing, as we explain in spotting products before prices rise.

How do the main tools handle days of cover?

Keepa shows the sales rank history and the offer counts behind any days of cover estimate, and its browser extension overlays them on the product page. It does not print the number for you. You read the chart, count rank drops and do the division yourself. That works for one ASIN before a purchase order, but not for a supplier list with 3,000 lines.

Bulk tools automate that arithmetic across lists. Each applies its own sales estimate and its own thresholds, so two tools can flag the same ASIN differently. The practical test is whether the tool lets you set your own threshold and see the evidence behind the number. Before you pay for anything, run five ASINs you already know well through it. If its estimate disagrees with what you have watched happen on those listings, trust your own count.

RipeBanana scores large ASIN lists on marketplace stock, sales pace and ROI, so you can narrow thousands of lines to a short list at the $49 to $99 tiers. Where it falls short: it does not replace Keepa for chart-level checks, and its sales figures are estimates. Run any flagged ASIN through the chart before you wire money to a supplier.

What mistakes do sellers make with days of cover?

What does a full buying decision look like?

Say a supplier list shows a kitchen gadget at $18 that sells for $34. Your profit calculator puts ROI at 22% after FBA fees, so the money side looks fine. Now check cover. The Keepa chart shows steady sales of about 40 units a day, and the listing holds about 200 units across all sellers. That is 200 ÷ 40 = 5 days of cover. Stock is nearly out, so the buy is worth a closer look.

Flip it. If 2,000 units sit on the listing at the same 40 a day, cover is 50 days. Other sellers will keep matching or undercutting your price for the next seven weeks, so that 22% ROI is not real. Skip it, add the ASIN to your tracker and recheck when cover drops under about 15 days.

What does “all of my days cover” mean in Amazon seller tools?

Some tools label their estimate this way to mean it includes your own position: units at Amazon, inbound shipments and sometimes stock at your supplier, divided by your average daily sales. It tells you how long your total stock would last, not just what sits in FBA warehouses today.

Is days of cover the same as days of inventory or stock days on hand?

They describe the same idea: current stock divided by average daily units sold. None of them is the same as “days to cover,” the short-selling metric. That formula belongs to stock trading and has no use in Amazon buying decisions.

Can you check days of cover for free before buying?

Yes. Keepa shows sales rank history, offer count and price history for free. Estimate daily sales from the rank drops, then divide the stock you can see by that figure. It works for one ASIN. It does not scale to a long supplier list.

Does low days of cover always mean a product is worth buying?

No. Low cover is the reason to look closer. Verify the chart first, because offer counts can collapse for reasons that are not scarcity. Low cover also says nothing about profit, so run ROI and competition checks before you commit capital.