Your Supplier's Quoted Lead Time Is a Sales Number. Measure Your Own.

The quoted number and your number aren't measuring the same thing

When a supplier tells you "two weeks," that number is usually honest. It's just answering a different question than the one you're asking. A quoted lead time typically starts counting at order acknowledgement, or at the point a production slot opens up, not on the day you sent the purchase order. And it often stops when the goods leave their dock, not when they arrive at yours.

So two real chunks of time live outside the quote and inside your reality. On their side, there's the gap between you sending the PO and them actually entering it, which can be a day or it can be a week depending on who's out. On your side, there's transit, plus however long a delivery sits on the dock before receiving logs it.

None of that is anybody lying to you. It's just that the supplier is quoting their clock and you're planning on yours. The number you need is the one that runs from the moment you commit to the moment you can sell the goods, and only your own records contain that.

The ten-minute version

You don't need software for the first pass. Pick one supplier, ideally the one you order from most, and export your closed purchase orders for them. Keep two columns:

Column	What goes in it
PO sent date	The day the order actually left your hands, not the day it was drafted
Received date	The day the goods physically landed and were logged into receiving
Real lead time	Received date minus PO sent date, in calendar days

Use calendar days, not business days. Your customer's expectations run on calendar days, and mixing the two is how a "ten day" lead time quietly becomes fourteen.

Do it for the last eight or ten closed orders. That's enough to see a shape. Fewer than five and you're looking at anecdotes, which is the same reason TraxSail won't hand a supplier a reliability grade until it has at least three POs to work from.

Then don't stop at the average

Most people compute the average and stop, which throws away the most useful half of what they just measured. The average tells you what a normal order looks like. It says nothing about how bad a bad order gets, and the bad ones are the only ones that cost you anything.

Here's the shape of it, using illustrative numbers rather than any real customer's data. Say a supplier quotes 14 days, and your last six receipts came in at 15, 16, 14, 22, 17 and 16 days:

Number	Value	What it's good for
Quoted lead time	14 days	Nothing, on its own. It's the supplier's clock.
Your average	16.7 days	Planning a normal reorder cycle
Your worst recent case	22 days	Anything you promise a customer
Spread	14 to 22 days	Deciding how much slack this supplier needs

Read that table and the picture changes. This supplier isn't unreliable, five of six orders landed within three days of each other. But the quote is two to three days optimistic on a normal order and eight days optimistic on a bad one. If you've been quoting your own customers off the 14, you've been wrong on every single order, by a little most of the time and by a lot occasionally.

The spread matters as much as either number. A supplier who runs a steady 20 days is easier to work with than one who averages 16 but swings between 12 and 24, because the steady one you can plan around exactly and the swingy one forces you to carry slack on every order. Consistency is worth more than speed, and the average hides which one you've got.

What to actually do with the number

Three decisions change once you have a real lead time and a real spread, and none of them require a conversation with the supplier:

• Move your reorder date, not your expectations. If the measured average is three days past the quote, your reorder trigger for that item moves three days earlier. Permanently. That's the whole fix, and it takes one field.
• Quote customers off the worst case, plan inventory off the average. These are different jobs for different numbers. Promising off the average means you are late roughly half the time, which is a strange thing to sign up for on purpose.
• Separate the slow supplier from the erratic one. A consistently slow supplier needs a bigger buffer. An erratic supplier needs a conversation, or a backup vendor qualified before you're forced into one under pressure.

Notice that the slow-but-steady supplier doesn't need to be confronted about anything. They're not failing. Your planning number was just wrong, and now it isn't. That's usually the most valuable outcome of the exercise, because it removes a recurring irritation without anybody having to have a difficult phone call.

The honest limits of the spreadsheet version

Two things break the by-hand version once you're past a handful of suppliers.

The first is that it goes stale. A lead time measured in March describes March. Suppliers change freight carriers, lose a shift, move a plant, get busy in Q4. The number is only useful if somebody recomputes it, and recomputing eight columns across thirty suppliers every quarter is exactly the kind of task that gets skipped in a busy month and then never restarted.

The second is that the by-hand version measures outcomes and not causes. You can see that an order took 22 days. You can't see from two date columns whether that was order-entry lag, a pushed ship date, or a carrier sitting on it, and those three have completely different fixes. Pairing lead time with date-push frequency and completion rate is what separates "this supplier is slow" from "this supplier commits to dates they don't hold."

If you want the arithmetic done on one supplier before you commit to anything, the free supplier grade calculator will take your own numbers and hand back a letter grade with the reasoning in plain words. No account needed.