Lead Time

Lead time is the amount of time that passes between the start of a process and its completion. In accounting and operations, the term most often means supplier lead time: the number of days between placing a purchase order and having the goods received and ready for use. It can also refer to manufacturing lead time, the time needed to turn raw materials into finished products, and customer lead time, the time between a customer's order and delivery.

Lead time matters to accountants because it determines how much inventory a business must hold to avoid running out, and therefore how much cash is tied up on the balance sheet. Longer and less predictable lead times force a company to carry more safety stock, which raises carrying costs and weakens working capital.

Supplier lead time is usually broken into several stages, each of which can be measured and improved separately:

• Order preparation, which covers the time needed to approve a requisition and issue the purchase order.
• Supplier processing, which is the time the vendor takes to pick, make or assemble the order.
• Transit, which is the shipping time and depends on distance, mode of transport and customs clearance.
• Receiving and inspection, which is the time needed to count, check and put the goods into stock.

For a manufacturer, production lead time adds queue time, setup time, processing time and waiting time between work stations. Each stage adds to the value of work in process sitting on the factory floor.

Lead time is a direct input into the reorder point, the inventory level at which a new order should be placed. The basic calculation is:

Here $\text{Daily usage}$ is the average number of units consumed per day, $\text{Lead time in days}$ is the average supplier lead time, and $\text{Safety stock}$ is a buffer held to cover delays or demand spikes.

Suppose a bakery uses 40 bags of flour a day, its supplier takes 6 days to deliver, and it keeps a buffer of 60 bags. The reorder point is 40 times 6, or 240 bags, plus 60, which is 300 bags. When stock falls to 300 bags, the bakery orders. If the supplier's lead time stretches to 10 days, the reorder point rises to 460 bags, and the bakery must finance an extra 160 bags of flour at any given moment. Lead time is also used alongside the economic order quantity (EOQ) model, which decides how much to order, while the reorder point decides when.

Long lead times increase average inventory, which lowers the inventory turnover ratio and raises days inventory outstanding (DIO). That in turn lengthens the cash conversion cycle, so the business needs more short-term financing. Lead time also affects when goods appear in the books: items shipped under FOB shipping point terms belong to the buyer while still in transit, so a long transit period can leave significant goods in transit to account for at period end.

Shortening lead time is a central aim of just-in-time manufacturing, which keeps inventory low by relying on frequent, reliable deliveries. The trade-off is greater exposure to supply disruption, as many companies found during the 2021 to 2022 shipping crisis, when ocean freight lead times from Asia roughly doubled and firms rebuilt buffer stocks.

Lead time is often confused with cycle time, which measures only the active work on an order, not the waiting before and after. Another common mistake is planning with a single average lead time and ignoring how much it varies; a supplier averaging 6 days but sometimes taking 14 needs a larger safety stock than one that reliably delivers in 8. Procurement teams often negotiate lead times alongside supplier payment terms, because a vendor that delivers faster and allows longer credit can sharply reduce the cash a business must commit to stock and to accounts payable management.