What is lead time? A guide for UK suppliers

The date on each order is a number you gave the buyer, coming back to you. In its October 2021 supplier manual, Travis Perkins explains where its due dates come from in a single bracket: "(The expected due date is generated from our agreed lead times held in POS)."

What is lead time?

The Cambridge Business English Dictionary defines lead time as "the time it takes after receiving an order to deliver the goods or services to a customer". The clock starts with the order, not with production.

The Lean Enterprise Institute's Lean Lexicon calls the same span order lead time and puts it from the customer's side: "In other words, the time the customer must wait for the product." It counts more than making and moving goods: time spent downstream, "including delays for processing orders and entering them into production".

So reading an order, keying it and booking the delivery all sit inside the lead time, before a single case is picked.

Software teams use the same term for a different measure of their own work, with no goods to deliver.

Order lead time, supplier lead time, production and delivery lead time: which is which?

Buyers and suppliers use different names for the same span. Each has a start, an end and an owner.

In the Lean Lexicon's terms, order lead time is production lead time plus the time spent getting the product to the customer, including order processing and the wait for capacity.

How is lead time measured?

Count from the order date to the date the delivery is received. That is the actual lead time on one order. The requested lead time runs from the same order date to the delivery date the customer asked for.

NHS Supply Chain publishes the only UK worked example we found. Its Operational Supplier Requirements, Version 4.1, online since March 2025, say of its Blue Diamond products: "All products will require a set lead time which is provided to the customer at point of order." For a three-day lead time, its example runs like this:

1. The customer places its order on Monday.
2. The supplier delivers to NHS Supply Chain on Wednesday.
3. NHS Supply Chain delivers to its customer on Thursday.

Read where the count stops. The three days run to Thursday, when NHS Supply Chain delivers to its own customer. The supplier's delivery is due on Wednesday, one day inside the set lead time. A supplier who counted all three days to its own delivery would plan for Thursday and arrive a day late.

The same document's Blue Diamond and eDirect sections show how order timing feeds the count. "Orders will be sent to suppliers throughout the day over eight order transmissions with the last transmission at 4.40pm." If your own cut-off falls before that, NHS Supply Chain puts the adjustment on you: "If there are cut offs for orders which impact the delivery lead time an additional day must be built into the set lead time."

Who sets your lead time? What UK buyers' supplier documents say

You supply or agree the figure. The buyer holds it on its own system and puts a date on each order from it. No document we read sets one lead time for every supplier. Each row below applies to that buyer's suppliers, under that document, at its date.

Lead times can change, through the buyer. M&S's 2019 handbook says: "M&S reserves the right to review supplier lead times and amend with the agreement of supplier at any time, but with reasonable notice." For eDirect products, NHS Supply Chain asks suppliers who keep delivering early to talk to it about amending the product's lead time.

Some buyers point to the order itself. Ocado's manual, dated September 2024, says: "Suppliers are required to meet the delivery in full, on the due date and at the time specified on the order."

Which EDI dates set and record your lead time?

Two GS1 EANCOM messages carry the dates: the purchase order (ORDERS) and the despatch advice (DESADV), the message behind an ASN.

The order opens the count. It carries its own date, "137 = Document/message date/time", which GS1 makes mandatory in an EANCOM message. Where the customer asks for a date, it adds "2 = Delivery date/time, requested". Those two dates bound the lead time your customer asked for.

The despatch advice records the other end. "11 = Despatch date and/or time" says when the goods left. The due date travels as "358 = Scheduled for delivery on or after" or "359 = Scheduled for delivery on or before". GS1's own sample despatch advice carries the despatch date (DTM+11), a due date of on or after (DTM+358) and the buyer's order number together. That lets the customer match the delivery to the order it measures you against. Receipt at goods-in closes the count.

Which dates your customer sends, and which it expects back, is set in its own message guide. An ASN, under GS1 UK's Perfect Order requirements (2016), should include "Delivery details including booking reference, delivery due date and time slot." The ASN guide covers the full message.

AG Barr mapped these fields when it moved customers' PDF and email orders onto EDI. In the AG Barr case study, the essential information included the "order date and requested delivery date".

Lead time vs cycle time, and lead time vs OTIF

Cycle time is one step. The Lean Lexicon says: "Cycle time is the time required to produce a part or complete a process, as timed by actual measurement." Lead time is the whole wait from order to delivery, queues, order handling and transport included. A fast picking step can sit inside a long lead time.

OTIF is the score. Lead time sets the date; OTIF records whether you met it. The OTIF guide puts on time plainly: "On time means the delivery arrived when the order said it should." At Travis Perkins, the date it scores against is the one generated from your agreed lead time.

Where does a supplier's time go between order and delivery?

The steps are our summary. The windows are each buyer's own.

1. The order arrives, by EDI, portal or email.
2. It is read and entered as a sales order. A sales order is "a supplier's own record of a customer's order that it has accepted to fulfil." Each line has to resolve to your own product code, because, as the SKU guide says, "your system has to know which is which before it can act on the order."
3. Receipt is confirmed and the delivery booked, inside the windows in the buyer table above.
4. The goods are picked, packed and despatched with an ASN.
5. The delivery arrives and is received. "At goods-in the warehouse scans each pallet's SSCC and matches it against the despatch advice that listed it before the goods arrived," as the SSCC guide describes.

Only steps 2 and 3 are about information, and they are the part EDI changes. An order rekeyed from a PDF still has to be read and typed before picking starts. If the customer changes the order, the purchase order guide covers how an order change works.

The date matters to the buyer too. Ocado's manual notes that "80% of customer orders are sold in advance of the physical arrival of stock on site," which the retail playbook covers alongside each buyer's delivery rules. The Lean Enterprise Institute describes the stock a business holds against late supply from its side: "safety stock protects you from incapability in your upstream processes and your suppliers."

Before a busy season, record each customer's booking rules alongside its lead times. The peak season checklist starts with each partner's peak calendar and booking rules.

How Transalis gets orders to you

Transalis is a managed outcomes provider for B2B integration, EDI and eInvoicing. Its EDI page names the step that costs order handling time and errors: "Rekeying orders from PDFs and emails into your ERP by hand."

"Transalis now offers EDI in three categories." Web EDI is a portal where your team "sees new orders the moment they land". Integrated EDI is "EDI wired directly into your ERP, accounting or warehouse system." Enterprise EDI is the third category. Suppliers not ready to connect an ERP can take the page's own path: "Start in a browser and grow into your ERP when you’re ready."

Map your supply chain from your customers' orders to the date on the dock.