Lead time is the input that quietly breaks every other calculation on this site. Reorder points, safety stock, cover: all of them take it as a given, and most stores have it wrong in the same direction, because they entered the number the supplier quoted rather than the time it actually takes to get stock onto a shelf.
Written August 2026. What Proviand stores per supplier and per product was checked against the production schema at the time of writing.
Stop using the quoted number. Measure the real one from your last three or four deliveries from each supplier, and use that. It takes about twenty minutes for a whole supplier list and it will change your reorder points more than any other single thing you could do.
The gap is usually 30 to 50 percent. A supplier who honestly quotes 14 days is frequently a 21 day lead time for you, and neither of you is lying. They are measuring their part. You have to live with the whole thing.
The quoted number almost always covers production and shipping. Here is everything that sits either side of it, with the ranges I see most often.
The two ends of that list are the ones stores forget, and they are the two ends they control. A store that approves POs once a week and counts deliveries in whenever someone has time can add ten days to every supplier without a single supplier being slow.
You do not need software for this. You need your last few purchase orders per supplier and two dates.
A worked example for one supplier:
Average: (19 + 22 + 20 + 23) / 4 = 21 days. Slowest: 23 days. If that supplier quoted 14, every reorder point you have for their products is built on a number that is seven days short.
What that costs, concretely. Take a product selling 3.86 units a day with 14 days of safety stock. At the quoted lead time the reorder point is ceil(3.86 x (14 + 14)) = 109 units. At the real one it is ceil(3.86 x (21 + 14)) = 136. You would place every order 27 units late, which at 3.86 a day is exactly the seven days you failed to count. Not occasionally. On every order, of every product, from that supplier, until you fix the number.
Here is the thing that surprises people: a supplier who reliably takes 30 days is easier to buy from than one who averages 20 but sometimes takes 45.
The reliable one is a planning problem. You know the answer is 30, you order 30 days out, and you are right nearly every time. The safety stock you need to cover them is small, because there is very little to cover.
The erratic one is a risk problem. Their average of 20 tells you almost nothing about the next order. Planning around 20 means being caught out by every 45 day delivery. Planning around 45 means carrying an extra 25 days of stock on every product they supply, permanently, to protect against something that happens occasionally. Either way you pay, and you pay on their whole range.
This is the direct link to safety stock. The practical safety stock formula uses max lead time precisely to absorb this, and the spread between a supplier's average and their worst case is a good first approximation of the buffer their products need. A supplier averaging 21 with a worst case of 23 needs almost nothing. One averaging 20 with a worst case of 45 needs weeks.
The actionable version: track the slowest, not just the mean. And when a supplier's spread gets wide enough, the cheapest fix is often a conversation rather than more stock. Suppliers rarely know that their inconsistency is costing you shelf space, because from their side each individual order arrived.
A single global lead time setting is the most common configuration mistake in this category, and it is expensive in both directions at once.
Set it to your slowest supplier and you carry weeks of unnecessary stock on everything from the fast ones. Set it to your fastest and you are permanently late on everything from the slow ones. Set it to the average and you achieve both, on different halves of your catalogue.
Lead time varies far more between suppliers than between products. The local distributor is three days. The factory overseas is eleven weeks. Nothing about a product changes that; almost everything about who supplies it does.
In Proviand lead time is stored on the supplier, defaulting to 14 days, with a per-product override for the cases where one item from a supplier genuinely behaves differently: a made-to-order variant in a catalogue that is otherwise stocked, or an item that ships separately. There is a shop-wide default underneath both, which exists so a new install computes something sensible on day one, not because it is where the number should live. If you do one piece of setup after installing anything in this category, make it entering real lead times per supplier.
What Proviand does not currently store is the variability: there is a lead time per supplier, not a distribution or a worst case. So the spread I have spent this page arguing matters is, for now, something you account for through the safety stock days you set rather than something the app derives from your PO history. That is on the list. I would rather say that plainly than imply the software is doing statistics it is not.
If you have one supplier, they are domestic, and they deliver in two or three days, the entire subject is a rounding error. Your reorder points are dominated by demand, not by supply, and you could set lead time to a flat number, never revisit it, and be right. Spend the time on merchandising instead.
The same applies if you buy to a fixed calendar rather than to demand: a store placing one seasonal order with a supplier per year is making a judgement call about a whole season, and the order-to-shelf arithmetic on this page has very little to add to it.
Lead time earns attention when it is long, when it varies, or when it differs across a supplier list. If all three are true, it is the highest-value number in your entire setup.
Proviand stores a lead time per supplier with per-product overrides, and shows it on every row of the buying table next to the cover figure it is being compared against, so a wrong lead time is visible rather than buried in settings.
Want a second pair of eyes on your supplier lead times? Email [email protected] with a few recent POs and I will work them out with you.
