Stock coverage: how many days you have, by channel

The question sounds simple: how many days will your current stock last? But if you sell on Amazon, on MercadoLibre, and move part of your inventory through a 3PL, the answer stops being a single number and turns into four scattered figures that almost never agree. You have units sitting in an Amazon fulfillment center, others in your own warehouse, others in transit, and each marketplace shows you a different sell-through speed. Your real coverage doesn’t live in any dashboard: it lives in your head, and it’s usually out of date.

The pattern is always the same. You open Amazon Seller Central to check FBA units, then MercadoLibre to look at Full and Flex, then the 3PL spreadsheet someone emailed you on Monday, and you end up pasting everything into an Excel file where you manually divide stock by what you think you sell per day. By the time you’re done, forty minutes have passed, the sales figure is from yesterday, and you make the decision of how much to order carrying all that uncertainty. Multiply that by every SKU and you understand why stockouts feel like an ambush instead of something you saw coming.

Stock coverage by channel is the metric that turns that chaos into a single actionable figure: how many days you have left before you run out, calculated per marketplace and consolidated for your business. It’s not a vanity number. It’s the data point that decides whether you order today, whether you pause a listing before it gets penalized, or whether you move units from one channel to another so you don’t lose sales.

what stock coverage actually is

Stock coverage, or days of inventory, is the result of dividing available units by your daily sell-through speed. If you have 300 units of a product and sell 10 a day, your coverage is 30 days. It sounds trivial, and it would be if you sold on a single channel with a single velocity. The problem starts when those 300 are split: 120 in FBA, 90 in MercadoLibre Full, 60 at your 3PL, and 30 in transit from the supplier.

Each of those blocks behaves differently. FBA units only serve Amazon demand. Full units only cover MercadoLibre. Your 3PL stock can feed Flex sales or self-fulfilled orders, but it won’t fix an FBA stockout without an inbound replenishment that takes days. That’s why an averaged “global” coverage misleads you: you can have 45 days of total stock and still run out on Amazon within a week because that’s where 70% of your sales happen but only 40% of your inventory sits.

Dictionary: days of inventory measure how long your stock will last at the current sales pace; it’s the translation from “units” to “time,” which is how a restock decision actually gets made.

why the average lies to you

The most common mistake the multichannel seller makes is calculating coverage by summing all stock and dividing it by total sales. That number looks healthy and gives you false comfort. The reality is that your channels don’t share inventory instantly. Each one is a compartment with its own demand and its own internal replenishment time.

Imagine SPORTIFY sells a sports knee brace. On Amazon it moves 25 units a day with 100 in FBA: 4 days of coverage, deep in the red. On MercadoLibre it sells 5 a day with 200 in Full: 40 days of coverage, more than enough. If you average it out, you’d say you have “11 days of stock” and sleep soundly. But Amazon, which is where the money is, runs dry on Thursday, loses the Buy Box, drops in organic ranking, and takes weeks to recover. The average hid the crisis.

That’s why coverage has to be calculated per channel first, and only then consolidated into a business-level view. Seeing both levels at once is what lets you tell apart “I need to buy more” from “I need to move what I already have from one channel to another.”

sell-through speed isn’t a single number

Here’s the second nuance that breaks the homemade calculation. Which velocity do you divide by? The last 7-day average? 30 days? 90? The answer dramatically changes your coverage.

A seasonal product like a fan in May has a 7-day velocity that triples its 90-day one. If you use the longer figure, you underestimate demand and run short right in peak season. A product that just came off a promotion has the opposite effect: its recent velocity is inflated, and if you buy based on it, you end up overstocked once it returns to normal.

Useful coverage accounts for several velocity windows and lets you choose which one weighs more depending on the SKU’s context. A good module doesn’t force you to decide blindly: it shows you coverage calculated over 7, 30 and 90 days side by side, so you can see whether the product is accelerating or decelerating before committing capital. This ties directly to how you run your real-time inventory: without fresh per-channel data, whatever velocity window you pick drags yesterday’s error along with it.

available isn’t the same as in the warehouse

A silent stockout happens when you confuse physical stock with sellable stock. Not every unit that shows up in a report is available for sale. There are units reserved for orders in progress, units in inspection or returns waiting to be restocked, aged inventory that FBA may be about to charge you long-term storage fees on, and stock blocked by listing issues.

If you calculate coverage on the big warehouse number instead of true available stock, your metric is inflated and you’ll believe you have headroom when you don’t. The correct calculation always starts from true available stock per channel: what can actually go out and sell today, after subtracting reservations, internal transfers, and non-sellable units.

Dictionary: true available stock is what you can sell right now, once reservations, returns in process, and blocked inventory are subtracted; it’s the honest basis for any coverage calculation.

a single source of truth, in real time

None of the above is sustainable by hand. You can do it once, for one SKU, in a good Excel sheet. But with dozens or hundreds of products spread across three or four channels, manual updating breaks on day two. Data ages, formulas drift out of sync, and you go back to deciding with yesterday’s information.

The reason a consolidated dashboard changes the game isn’t that it looks nice, but that it removes the step of gathering the information. Instead of three tabs, a 3PL email, and a spreadsheet, you have a single screen that reads true available stock from each channel, cross-references it with the current sell-through speed, and hands you coverage in days, by channel and consolidated, without you touching a single data point. When a SKU goes red on Amazon while it’s overstocked on MercadoLibre, you see it immediately, not the following Monday.

That visibility is what feeds decisions you used to make blind. Knowing your coverage by channel is the direct input to restock recommendations: you can’t know what to order this week if you don’t know how many days you have left in each marketplace. And coverage also talks to your profitability: if you’re going to rush a purchase to avoid a stockout, it’s worth checking your minimum profitable price first, because an urgent restock with express freight can eat the margin you thought you had.

how to read coverage to decide

Coverage on its own doesn’t tell you what to do; it tells you how much time you have to do it. The right reading combines three things: the channel’s days of coverage, that channel’s replenishment lead time, and the recent velocity. If your FBA coverage is 18 days but your replenishment takes 21 from production to warehouse arrival, you’re already late even though the number looks comfortable.

That’s why the metric only makes sense when compared against a threshold specific to each SKU, not against a generic number. A high-rotation product with a short lead time can run comfortably on 15 days of coverage. An imported one with three months of transit needs 90 or more to avoid a stockout. Coverage warns you; the threshold tells you whether the warning is urgent.

Dictionary: true net margin is what’s actually left after fees, shipping, and costs; it’s worth cross-checking against coverage so you don’t save a sale at the expense of your profit.

the cost of not measuring it

Running out of stock isn’t just losing the sales of the days you’re sold out. On Amazon, a stockout tanks your organic ranking and can cost you the Buy Box; recovering the position takes weeks and often demands extra ad spend. On MercadoLibre, it hurts your reputation and the listing’s visibility. Overstock has the opposite problem: frozen capital, long-term storage fees in FBA, and the risk of having to liquidate at a discount products that aged in the warehouse.

Stock coverage by channel is the metric that keeps you between those two cliffs. You don’t calculate it to have one more figure on a dashboard: you calculate it to buy the right quantity, at the right time, in the right channel. And to do it well, you need to stop pasting numbers by hand and start reading them from a single source that is always up to date.