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{{More citations needed|date=December 2009}}
A '''lead time''' is the [[:wikt:latency|latency]] between the initiation and execution of a process. For example, the lead time between the placement of an order and delivery of a new car from a manufacturer may be anywhere from 2 weeks to 6 months.

==Journalism==
Lead time in [[publishing]] describes the amount of time that a [[journalist]] has between receiving a writing assignment and submitting the completed piece. Depending on the publication, lead times can be anything from a couple of hours to many months/years.

==Medicine==
Lead time (when referring to a disease) is the length of time between detection of a disease through screening and the moment in time where it would have normally presented with symptoms and led to a diagnosis. An example of this is seen with breast cancer population screening, where women who are asymptomatic have a positive test result with mammography, whereas the underlying disease would have taken many more years to manifest.

==Supply chain management==
A more conventional definition of lead time in the [[supply chain management]] realm is the time from the moment the customer places an order (the moment the supplier learns of the requirement) to the moment it is ready for delivery. In the absence of [[finished goods]] or intermediate (work in progress) inventory, it is the time it takes to actually manufacture the order without any inventory other than raw materials. The [[Chartered Institute of Procurement & Supply]] identifies "total lead time" as a combination of "internal lead time" (the time required for the buying organisation's internal processes to progress from identification of a need to the issue of a [[purchase order]]) and "external lead time" (the time required for the supplying organisation's processes, including any [[New product development|development]] required, manufacture, despatch and delivery).<ref>CIPS in partnership with Profex Publishing, ''Procurement and Supply Operations'', 2012, revised 2016, pp. 64-65</ref>

==Manufacturing==
In the manufacturing environment, lead time has the same definition as that of Supply Chain Management, but it includes the time required to ship the parts from the supplier. The shipping time is included because the manufacturing company needs to know when the parts will be available for [[material requirements planning]]. It is also possible for lead time to include the time it takes for a company to process and have the part ready for manufacturing once it has been received. The time it takes a company to unload a product from a truck, inspect it, and move it into storage is non-trivial. With tight manufacturing constraints or when a company is using [[Just In Time (business)|Just In Time]] manufacturing it is important for supply chain to know how long their own internal processes take.

Lead time is made of:<ref>[http://en.supply-chain-consultant.eu/10/lead-time-supply-chain/ ''Lead Times'']. "Lead times in supply chain" Supply Chain Consultant Website.</ref>
* '''Preprocessing Lead Time''' (also known as "planning time" or "paperwork"): It represents the time required to release a purchase order (if you buy an item) or create a job (if you manufacture an item) from the time you learn of the requirement.
* '''Processing Lead Time''': It is the time required to procure or manufacture an item.
* '''Postprocessing Lead Time''': It represents the time to make a purchased item available in inventory from the time you receive it (including quarantine, inspection, etc.)

'''Example'''

Company A needs a part that can be manufactured in two days once Company B has received an order. It takes three days for company A to receive the part once shipped, and one additional day before the part is ready to go into manufacturing.
*If Company A's Supply Chain calls Company B they will be quoted a lead time of 2 days for the part.
*If Company A's Manufacturing division asks the Supply Chain division what the lead time is, they will be quoted 5 days since shipping will be included.
*If a line worker asks the Manufacturing Division boss what the lead time is before the part is ready to be used, it will be 6 days because setup time will be included.

'''In more detail'''

Lead Time terminology has been defined in greater detail.<ref>Rajaniemi, J. (2012) [http://www.leadtimes.org/ ''www.leadtimes.org''] Lead Time Terminology in Manufacturing.</ref> The Supply Chain from customer order received to the moment the order is delivered is divided into five lead times.
* '''Order Lead Time''' - Time from customer order received to customer order delivered.
* '''Order Handling Time''' - Time from customer order received to sales order created.
* '''Manufacturing Lead Time''' - Time from sales order created to production finished (ready for delivery).
* '''Production Lead Time''' - Time from start of physical production of first submodule/part to production finished (ready for delivery).
* '''Delivery Lead Time''' - Time from production finished to customer order delivered.

'''Example '''

A restaurant opens up and a customer walks in. A waiter guides him to a table, gives him the menu and asks what he would like to order. The customer selects a dish and the waiter writes it in his notepad. At that moment the customer has made an order which the restaurant has accepted – Order Lead Time and Order Handling Time have begun. Now the waiter marks the order in the cash register, rips the paper from the notepad, takes it into the kitchen and puts into the order queue. The order has been handled and is waiting in the factory (kitchen) for manufacturing. As there are no other customers, the waiter decides to stand outside the kitchen, by the door, waiting for the dish to be prepared and begins calculating Manufacturing Lead Time.

Meanwhile, the chef finishes what he was doing, takes the order from the queue, starts his clock as a mark for the start of Production Lead Time and begins cooking. The chef chops the vegetables, fries the meat and boils the pasta. When the dish is ready, the chef rings a bell and stops his clock. At the same time the waiter stops calculating Manufacturing Lead Time and rushes through the kitchen door to get the food while it is hot.

When he picks it up, begins counting of Delivery Lead Time that ends when the dish is served to the customer, who can now happily say that the Order Lead Time was shorter than he had expected.

==Order lead time==
When talking about Order Lead Time (OLT) it is important to differentiate the definitions that may exist around this concept. Although they look similar there are differences between them that help the industry to model the order behavior of their customers. The four definitions are :
*The '''Actual Order Lead Time ''' (OLTActual)<ref>Kumar, A. (1989). Component inventory costs in an assembly problem with uncertain supplier lead-times. IIE transactions, 21(2), 112-121.</ref> The order lead-time'', refers to the time which elapses between the receipt of the customer's order (Order Entry Date) and the '''''delivery''''' of the goods."<ref>Gunasekaran, A., Patel, C., & Tirtiroglu, E., 2001 "Performance measures and metrics in a supply chain environment." International journal of operations & production Management 21, no. 1/2: 71-87.</ref>
*The '''Requested Order Lead Time ''' (OLTRequested) represents the time between the Order Entry Date and the customer '''''requested''''' delivery date; this measurement could help the company to understand the order behavior of the customers and help to design profitable models to fulfill customer needs.<ref>2)Cousens, A., Szwejczewski, M., & Sweeney, M. 2009. "A process for managing manufacturing flexibility." International Journal of Operations & Production Management, 29(4), pp.357-385.</ref><ref name="test">Silva, L., 2013, "Supply Chain Contract Compliance Measurements" Master thesis (work in progress), Aalto University, Finland.</ref>
*The '''Quote Order Lead Time ''' (OLTQuote) is the '''''agreed'' ''' time between the Order Entry Date and the supplier’s committed deliver date of goods as stipulated in a supply chain contract.<ref name="test" />
*The '''Confirmed Order Lead Time''' (OLTConfirmed) represents the time between the Order Entry Date and the by the supplier '''''confirmed''''' delivery date of goods.<ref name="test" />

[[Image:OLT Definitions.jpg|thumb|OLT Definitions<ref name="test" />]]

=== OLT formulas ===
*OLTRequested = Wish Date – Order Entry Date
The OLTRequested will be determined by the difference between the date the customer wants the material in his facilities (wish date) and the date when they provided its order to the supplier.
*OLTQuote = Quote Date – Order Entry Date
The OLTQuote will be determined by the difference between the date the customer agree to receive the material in their facilities (Quote date) and the date when the order is provided to the supplier.
*OLTActual = Delivery Date – Order Entry Date
The OLTActual will be determined by the difference between the day the provider deliver the material (Delivery date) and the date when they enter the order in the system.
*OLTConfirmed = Confirmed Date – Order Entry Date
The OLTConfirmed will be determined by the difference between the date the confirmed date by the provider to deliver the material in the customer facilities (Confirmed date) and the date when they provide the order to the supplier.

===Average OLT based on volume===
The Average OLT based on Volume (OLTV) is the addition of all the multiplications between the volume of product we deliver (quantity) and the OLT divided by the total quantity delivered in the period of time we are studying for that specific facility. 
<math>OLTV= \frac{\sum_{j}{Quantity_j \cdot OLT_j}}{_{Total Quantity Deliver}} \,</math> 
By doing this the company will be able to find a relation of volume weighted between the quantities of material required for an order and the time requested to accomplish it. The volume metric could be applied to the 4 types of OLT. 
The figure obtained from this calculation will be the average time (e.g. in days) between order placing and the requested delivery date of a specific customer under consideration of the average quantities ordered during that particular time.

===Potential application areas for order lead time measurement===
The correct analysis of OLT will give the company:
*Better understanding of the market behavior making it able to develop more profitable schemas that fit better with customer needs (Revenue Management).
*Increases company ability to detect and correct any behavior that is not within terms agreed in the contract (by penalization or different contract schema).
*The OLT measurement creates an opportunity area to improve the customer relations by increasing the level of communication with them.

==Project management==
In [[project management]] lead time is the time it takes to complete a task or a set of interdependent tasks. The lead of the entire [[project]] would be the overall duration of the [[critical path method|critical path]] for the project.

Lead time is also the saved time by starting an activity before its predecessor is completed.

According to the PMI (2008), lead is a dependency between two activities (p. 140).<ref>PMI. (2008). A guide to a project management body of knowledge (4th. ed.). ''The Project Management Institute''. Newton Square, PA: PMI Publications.</ref> An example would be scheduling the start of a 2-week activity dependent with the finish of the successor activity with a lead of 2 weeks so they will finish at the same time.

==See also==
*[[Time limit]]
*[[Safety stock]]
*[[Latency (engineering)]]

==References==
{{Reflist}}

{{DEFAULTSORT:Lead Time}}
[[Category:Publishing]]
[[Category:Lean manufacturing]]
[[Category:Business planning]]

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