What Is Lead Time?

Lead time is the period between placing an order and having the goods ready to use - not just the courier’s transit days, but everything from the purchase order leaving your hands to the items sitting checked-in on your shelf. It is the single number that decides when a reorder must happen: order earlier than the lead time demands and cash sits in excess stock, order later and the stock level hits zero before the delivery arrives.

What lead time includes

The full span has four legs, and the invisible ones at each end are the ones people forget:

• Order processing - the time the order spends in the supplier’s queue before anyone acts on it.
• Production or picking - making the item, or pulling it from the supplier’s own stock.
• Transit - the shipping leg most people picture when they say “lead time”.
• Receiving - your side: goods-in checks, inspection, putting items away, updating the records. Stock that sits unbooked on a loading dock is not yet usable stock.

How to calculate lead time

For one order, the maths is just subtraction:

Lead time = date goods were ready to use - date order was placed

For planning, average it across the last several orders from the same supplier - and record the spread, not only the mean. A supplier averaging ten days with a range of five to twenty is a different planning problem from one that lands between nine and eleven every time, even though the averages match. Variability, more than length, is what forces safety stock upward.

Supplier, production and customer lead time

The same word covers three perspectives. Supplier lead time is how long your vendors take to fulfil your purchase orders. Production lead time is how long your own operation takes to make something once materials are in hand. Customer lead time is the promise you make outward - how long your customers wait for you. The three are linked: you can only quote a short customer lead time if supplier and production lead times are covered by stock you already hold. Delivery time, by contrast, is just the transit leg, which is why a “48-hour delivery” supplier can still have a two-week lead time.

Lead time and reorder points

Lead time earns its keep in the reorder point formula:

Reorder point = (average daily usage × lead time in days) + safety stock

Using 5 units a day against a 10-day lead time means the reorder must trigger at 50 units plus a buffer - say 15 units of safety stock, giving a reorder point of 65. Lean strategies like just-in-time inventory work by shrinking lead times until buffers become almost unnecessary; seasonal businesses face the opposite case, with one long lead time and one immovable deadline - a ski-hire shop ordering rental equipment works backwards from opening day, because no safety stock rescues an order placed too late. For internal consumables, a register like AMPthilly keeps a reorder point and supplier on each item, so the buy decision is triggered at the reorder point rather than at the empty shelf.

Shortening lead time

Some levers sit with the supplier: closer or second-source vendors, blanket orders the supplier can fulfil from their own stock, and sharing forecasts so they produce ahead of your order. Others are internal and cheaper: place orders the day the reorder point trips rather than batching them for month-end, and keep receiving fast so goods become usable stock the day they arrive. None of it works without honest records - a reorder point checked against a wrong on-hand quantity fires too late or not at all.

Related terms

• Stock Level - the on-hand quantity a reorder point watches
• Just-in-Time Inventory - the strategy built on short, reliable lead times
• Inventory Management - the wider discipline reorder timing sits inside
• Inventory Accuracy - why the quantity the formula reads must match the shelf
• Dead Stock - the result of over-ordering against a lead time that was never that long