What Is Lead Time and How to Measure Yours Accurately

Lead time is the real amount of time that passes between the moment you place a replenishment order and the moment those units are ready to sell on your channel. It is not what the supplier promises, and it is not what the contract says: it is what it actually takes, end to end, from sending the order to seeing that stock go live and sellable on Amazon, on MercadoLibre, or through your 3PL. Measuring it correctly is the difference between reordering on time and discovering a stockout after you have already lost the Buy Box.

The most common mistake is believing lead time is just transit. You think “the supplier takes 30 days to ship,” and that becomes your number. But between sending the order and selling the first unit there are many more steps: the supplier takes time to produce, the goods travel, they clear customs, they arrive at your warehouse or the marketplace’s receiving center, they get inspected, they get listed, and only then are they sellable. Every one of those legs adds days, and almost none of them show up in the supplier’s promise. Your real lead time is the sum of all of them, not just one.

That is why measuring yours accurately means dropping the number you assume and using the one your own data shows. If you have a record of when you ordered and when those units became sellable, you already have the honest figure. The problem is that this record almost never lives in one place: the order date sits in an email, the receiving date in the marketplace panel, the go-live date in another tab, and stitching them together by hand is exactly what nobody does with the consistency it requires.

what lead time actually is

Lead time, in the most useful definition for a seller, is the full replenishment cycle measured in days: from the moment you issue a purchase order to the moment the unit is available to sell on the channel where you will sell it. The key word is “available”: it does not count when the box touches your warehouse, it counts when the marketplace’s system already shows it sellable and it can go out in a customer’s next order.

That distinction is not a technicality. Between the goods physically arriving and them becoming sellable there can be days of receiving, inspection, labeling, and listing. In FBA, for example, inventory can sit in the fulfillment center for several days before showing up as available; in MercadoLibre Full something similar happens. If you measure your lead time up to “it reached the warehouse” and not up to “it became sellable,” you underestimate the number precisely in the leg that is most likely to cost you a stockout.

That is why it helps to think of lead time as a chain of links: supplier production time, transit time, customs time, receiving time, listing time. Your real lead time is the sum of all of them, and each link has its own variability. Measuring only the most visible one (transit) and assuming the rest are zero is the recipe for always reordering late.

why the number you assume is almost always wrong

The lead time most people use is a round number inherited from an old conversation: “the supplier takes about a month.” That number has three problems. First, it is a promise, not a measurement: it reflects what someone said, not what happened. Second, it is an informal average, so it ignores real variability, and in replenishment variability matters as much as the average. Third, it measures a single link and treats the rest as if they did not exist.

The result is a systematically optimistic lead time. If your real number is 45 days but you plan with 30, every order lands fifteen days later than your assumption, and those fifteen days are exactly the gap where a stockout sneaks in. The worst part is that the error is silent: since you never compare the date you ordered against the date you could actually sell, you never find out your assumption is wrong until a product runs out and you cannot replenish in time.

Glossary: a stockout is running out of sellable units on a channel; an underestimated lead time is one of the most frequent causes, because it makes you reorder late while believing you are on time.

how to measure your lead time with data, not assumptions

Measuring lead time accurately is surprisingly simple once you have the two right dates: the date you placed the order and the date those units became available to sell. The difference between them, in days, is your real lead time for that replenishment. Do it for several orders of the same SKU and the same supplier, and you will have something far more valuable than an average: a distribution.

That distribution is what tells the truth. The average gives you the center (say, 40 days), but what you need to plan without stocking out is the high end: if out of ten orders the slowest took 58 days, planning with 40 leaves you exposed almost half the time. The healthy practice is to use a high percentile, not the average: if in 90% of your orders the stock became sellable in 52 days or less, that 52 is your planning lead time. You will “have extra” sometimes, but you will almost never fall short.

For this calculation to be sustainable you need to record, order by order, three moments: when you sent the order, when it physically arrived, and when it became sellable. With those three points you get not only the total lead time but also where the time is going. If transit is stable but receiving spikes, the problem is not the supplier: it is your internal process or the fulfillment center, and the fix is different.

lead time changes by channel and by SKU

An expensive mistake is treating lead time as a single number for your whole catalog. In reality it changes by product and, above all, by channel. The same SKU can have 12 days of lead time to your own warehouse and 40 to FBA, because on top of the supplier’s transit you add the shipment to Amazon plus their receiving and listing time. If you plan both channels with the same number, one of them will be miscalibrated.

It also changes by origin. An imported product with 60 days of ocean transit has a completely different lead time than one from a local supplier who delivers in 5. Blending them into a catalog average produces a number that describes neither: too high for the local one, too low for the imported one. Useful lead time is measured per SKU and per channel, not as a constant of your operation.

This is one of the reasons it pays to separate the legs. As we develop in supplier lead time vs lead time to the marketplace, the time your supplier controls and the time the channel’s logistics adds are different beasts: they are measured differently, improved differently, and confusing them makes you optimize the wrong link.

Glossary: days of inventory measure how long your stock will last at the current sales pace; comparing days of inventory against your real lead time is what tells you the exact moment to reorder.

what lead time is for once you measure it

Lead time is not a curiosity metric: it is the main input into almost every replenishment decision. The reorder point (when to order) is calculated by multiplying your daily sales velocity by the lead time, plus a safety buffer. If your real lead time is 45 days and you sell 10 units a day, you need to trigger the order when you have around 450 sellable units left, not when you are down to 100 and it is already too late.

That is why lead time and real available stock work together. Knowing your lead time is useless if you calculate days of coverage on the physical warehouse stock instead of what you can actually sell today. The honest math always starts from real available stock per channel, already net of reservations, internal transfers, returns pending processing, and blocked units. That number, divided by your sales velocity, gives you the days you have left; and those days, compared against your lead time, tell you whether it is already time to order.

Glossary: real available stock is what you can sell right now, once reservations, returns, and blocked inventory are subtracted; it is the honest base against which lead time is crossed to decide when to reorder.

why real-time changes everything

Everything above can be done once, for one SKU, in a good spreadsheet. The problem shows up when you have dozens or hundreds of products across three or four channels, each with its own lead time, its own sales velocity, and its own real available stock changing every day. That is where the manual method breaks: you open Seller Central to check FBA, then MercadoLibre for Full, then the 3PL sheet that arrived by email, you hunt for the date you ordered each thing, and by the time you finish stitching it together the data is already from yesterday, and you make the reorder decision carrying that uncertainty.

Real-time solves exactly that bottleneck. Instead of you reconstructing order and go-live dates by hand, the system logs each replenishment, calculates the real lead time per SKU and per channel from your own events, crosses it with the current sales velocity and the real available stock, and tells you which products are entering the reorder zone before they stock out. This leans on your real-time inventory: without fresh data per channel, any lead time calculation drags yesterday’s error and makes you reorder late again.

When you also consolidate several warehouses into a single view, lead time stops being an isolated number and becomes actionable: you see at a glance which channel is short, how long it would take to replenish it, and whether it makes sense to reorder or simply move stock from where there is a surplus. That jump, from manual monitoring to automatic alerts on fresh data, is what we develop in multi-warehouse inventory: how to consolidate your stock in one view, and it is what turns lead time from a figure you jot into a spreadsheet into an alert that warns you on time.

in short

Lead time is the real end-to-end time between ordering and being able to sell, not the supplier’s promise or transit alone. You measure it by subtracting the order date from the date the stock became sellable, you plan with a high percentile instead of the average, and you calculate it per SKU and per channel because it differs in each one. Measured well and crossed with your real available stock and sales velocity, it stops being an assumption that makes you reorder late and becomes the signal that tells you the exact day to reorder. And for that calculation to hold up across dozens of products in several channels, it needs real-time data, not a sheet that ages every night.