Ask what the lead time is on a component and you’ll get a single number. That number is in your item master, your MRP runs on it, and your planners quote from it. It is almost certainly not a fact — it’s a quote, and the actual distribution behind it is usually wider and later than the quote suggests.

Variability Costs More Than Length

This is the counterintuitive part. A supplier who reliably delivers in thirty days is easier and cheaper to plan around than one who delivers somewhere between eight and twenty-two.

Long lead times you can plan for — order earlier. Variable lead times you have to buffer against, and the buffer has to cover the worst case, not the average. The inventory carrying cost of unpredictability is frequently larger than the price premium of a more reliable supplier, which is a comparison almost nobody runs.

Measure the Distribution

Start by replacing the single number with real data. For each significant component, pull order dates and receipt dates over the last year or two and look at the spread: median, worst case, and how often the quoted lead time was actually met.

Several things usually emerge. Quoted lead times are optimistic across the board. Variability differs enormously between suppliers of similar items. Some suppliers are consistently late by a stable amount, which is easy to correct for. Others are erratic, which is the genuinely expensive pattern.

That distinction drives different responses. Consistent lateness is a master data fix — change the planning lead time to what actually happens. Erratic delivery is a supplier conversation or a sourcing decision.

Reducing the Variability

Share forecasts. A large share of supplier lead time variability comes from their own capacity planning against uncertain demand. Give them visibility and their reliability usually improves, because they can plan rather than react.

Understand where you sit in their priority order. A supplier allocating scarce capacity serves their most important customers first. If you’re small to them, your lead time will stretch precisely when supply is tight — which is exactly when you need it not to.

Ask what actually drives their lead time. Sometimes it’s their own inbound material, in which case your exposure is really to a tier-two supplier. Sometimes it’s a batching or scheduling decision that could change with a conversation. You won’t know without asking.

Consider scheduling agreements over discrete orders. A committed volume schedule lets suppliers hold material and shortens their response time, often at no additional cost.

Planning Against Reality

Whatever the variability is, plan against measured distributions rather than quoted figures, and size safety stock from the actual spread. And review the numbers periodically — lead times drift upward slowly during tight supply and rarely get revised back down.

One more thing worth tracking: which of your own behaviours contribute. Late requisitions, frequent order changes, and rush requests all train suppliers to quote defensively. A share of the variability you’re planning around may be a response to how you order.

ticktick.ai maintains lead time distributions per supplier and item from receipt history, and uses them in planning rather than the quoted figure.