How to calculate lead time
Lead time is the elapsed time between committing to an order and having the goods available to sell — in this guide, the calendar days from the date a purchase order is issued to the date the units are received, checked and sellable. Both ends are choices. Start at the buy decision and the figure absorbs your own approval lag; end at ex-factory or DC receipt and it omits days the plan still waits. The receipt plan needs the version that ends when stock can sell, because that is the week the receipt lands in the WSSI.
Project one order in the lead-time and OTD calculator and lay out its milestones in the T&A calendar template. The in-store dates come from how to plan receipt flow, and a slipped receipt week shows first in how to read a WSSI.
All dates, durations and quantities in the worked figures are illustrative — not benchmarks, and not drawn from any brand or vendor.
- Definition — Lead time
- Lead time is a duration between two named events, so a lead time quoted without its start and end events cannot be compared with any other.
- Lead time (days) = sellable date − PO issue date = Σ days between consecutive milestones
- Used by: Planners, buyers, sourcing and production teams — to schedule the T&A calendar, place POs, size buffers and set chase and reorder dates
- Related: On-time delivery, cycle time, T&A calendar, intake, open-to-buy, reorder point
- Lead time = sellable date − PO issue date, in calendar days; record ex-factory and DC receipt too.
- Segments between consecutive milestones must sum to the total, or a milestone is missing.
- Attribute variance to decision, vendor, origin-to-port and destination — a late PO is not a late vendor.
- Plan from the spread, not the average: the buffer is days for a seasonal delivery and units for a replenished style.
- Lead time sets the latest chase PO, the reorder point and whether an OTB reserve can still be spent.
Which events to measure between, and why the choice matters
A lead time is comparable only with another measured between the same two events. The candidate starts are the buy approval, the PO issue date, the vendor’s acknowledgment and the material order; the candidate ends are ex-factory, departure, arrival at the destination port, DC receipt and sellable. Each pairing suits a different owner.
The vendor controls PO to ex-factory, so that is the segment a vendor can commit to and be scored on. The forwarder and carrier control ex-factory to arrival; the brand controls the decision before the PO and the days from arrival to sellable. The plan needs PO to sellable, because a receipt counts in the week stock can sell, not the week it leaves a factory — a plan built on the vendor’s segment omits 40 planned days in the worked example below.
Starting at the PO rather than the buy approval is deliberate too. The days between approving a buy and issuing the PO are real and they move the in-store date, but they are the brand’s: measure them as a separate decision segment, so a PO that leaves five days late is not charged to a vendor that had no order. And count calendar days — the intake week sits on the calendar, so a factory quote in working days is converted through the factory’s own calendar before it enters the plan.
Date subtraction, and the identity that checks it
- Lead time = sellable date − PO issue date
- Segment = later milestone date − earlier milestone date
- Lead time = Σ segments from PO issued to sellable
- Lead-time variance = actual lead time − planned lead time
- Slip against the planned date = decision-lag variance + lead-time variance
The third line is the check: date every hand-off and the segments sum to the total exactly; if they do not, a milestone is missing or parallel tracks — fabric and sampling, say — were mixed. The last line is why goods can land later than their lead-time variance: the plan was scheduled from the planned PO date, not the actual one. A lead time says how long the order took; the slip says how late the goods are, and only the slip moves the receipt week. The lead-time and OTD calculator runs the forward version for a single order.
What sits between the buy decision and the sales floor
Nine segments, in order. A domestic truckload has no sailing and a repeat on approved materials has a short approvals segment, but naming each segment is what lets a variance be attributed rather than argued about.
- 1
Decision and PO placement
Buy approval to a PO the vendor can act on: costing closed, sizes split, terms agreed. It precedes the PO, so it sits outside both the vendor’s and the planning lead time but inside the schedule to the in-store date; measure it as its own segment.
- 2
Sampling and approvals
Lab dips, print strike-offs, trims, fit and pre-production samples. Each approval is a round trip, so a rejected round adds a whole cycle; record the rounds beside the dates.
- 3
Raw materials and fabric
Fabric, trims and packaging. Stock-supported or greige-held material shortens the segment; developed or dyed-to-order material lengthens it. Where two run in parallel, the later one gates the cut.
- 4
Production
Cutting, sewing or assembly, finishing and packing — the production cycle time. Date the wait for a capacity slot separately, or a queue reads as slow sewing.
- 5
Quality control
In-line and final inspection. A failed final inspection adds rework and a second booking, and goods are not released until it passes, so measure to inspection passed.
- 6
Ex-factory
Handover of inspected goods at origin: documents, booking and delivery to the freight station or yard. It ends the vendor’s segment and is the date an FOB order changes hands.
- 7
Transit by mode
Ocean, air, rail or truck differ in transit days, departure frequency and variability. A scheduled leg turns lateness into steps: cargo that misses a booking cutoff waits for the next departure.
- 8
Customs
Entry filing, duty and any examination or documentation hold. The documents are prepared at origin, so this delay is created before departure and discovered after arrival.
- 9
DC receipt to sellable, and to the floor
Unloading, counting against the PO, receiving inspection, ticketing, putaway and allocation. For stores add DC-to-store transit and the floor set; for DTC, sellable is when units show as available to sell.
Six steps, in order
Steps two and three are recording and subtraction. Steps one and four decide whether the figure can be acted on — a lead time between unstated events, or a variance nobody attributed, turns a late delivery into a debate.
- 1
Fix the start and end events
For planning, measure from the PO issue date to the sellable date in calendar days, recording ex-factory and DC receipt between them. Write the definition down, so two teams are not comparing different events.
- 2
Record the actual date of every milestone
Date each hand-off when it happened, from PO issued through approvals, materials, cut, production, inspection, ex-factory, departure, arrival and customs to receipt and sellable. An undated segment cannot be attributed later.
- 3
Subtract to get each segment and the total
Each segment is the later milestone date minus the earlier one. The segments must sum to the sellable date minus the PO date; if they do not, a milestone is missing or parallel tracks were mixed.
- 4
Compare with plan and attribute the variance
Group the variances into decision, vendor, origin-to-port and destination, so a late PO is not recorded as a late vendor. The slip the receipt plan feels is the decision variance plus the lead-time variance.
- 5
Measure variability across like-for-like deliveries
Group completed deliveries by vendor, product type, lane, mode, and new or repeat. Read the range, the standard deviation and how many deliveries took longer than the figure the plan used.
- 6
Turn variability into a buffer and back-schedule
Hold the chosen margin as calendar days for a seasonal delivery or as units for a replenished style, then work backward from the in-store date through each segment to the latest PO date.
One delivery on the shared season, milestone by milestone
The illustrative six-month season from the sales-plan, receipt-flow and GMROI guides, one class, in thousands of retail dollars: month-three receipts of 290, without the shrink provision. Two assumptions put it on a calendar: a 4-5-4 calendar whose week 1 begins Monday 2 August 2027, with weeks running Monday to Sunday, so month three is weeks 10 to 13, 4 to 31 October; and month three’s 290 lands as 150 in week 10 and 140 in week 12. This is the week-12 delivery — one knit style group, one vendor, ocean freight, an in-store date of Monday 18 October.
Back-scheduled with a 7-day buffer, the plan had the goods sellable by Monday 11 October and the PO issued on Wednesday 2 June, 131 days earlier. Plan and actual days count from the milestone above; all dates are 2027.
| Milestone | Plan date | Actual date | Plan days | Actual days | Days late |
|---|---|---|---|---|---|
| Buy approved | Wed 26 May | Wed 26 May | — | — | 0 |
| PO issued | Wed 2 Jun | Mon 7 Jun | 7 | 12 | +5 |
| Lab dips and trims approved | Wed 16 Jun | Mon 21 Jun | 14 | 14 | +5 |
| Bulk fabric in-house | Wed 14 Jul | Wed 21 Jul | 28 | 30 | +7 |
| PP sample approved | Fri 23 Jul | Mon 2 Aug | 9 | 12 | +10 |
| Cut started | Wed 28 Jul | Thu 5 Aug | 5 | 3 | +8 |
| Production complete | Wed 25 Aug | Wed 1 Sep | 28 | 27 | +7 |
| Final inspection passed | Fri 27 Aug | Mon 6 Sep | 2 | 5 | +10 |
| Ex-factory | Wed 1 Sep | Thu 9 Sep | 5 | 3 | +8 |
| Vessel departed | Sat 4 Sep | Sat 18 Sep | 3 | 9 | +14 |
| Arrived at destination port | Sat 2 Oct | Sat 16 Oct | 28 | 28 | +14 |
| Customs released | Tue 5 Oct | Thu 21 Oct | 3 | 5 | +16 |
| Received at DC | Fri 8 Oct | Mon 25 Oct | 3 | 4 | +17 |
| Sellable | Mon 11 Oct | Thu 28 Oct | 3 | 3 | +17 |
| Lead time, PO issued to sellable | — | — | 131 | 143 | +12 |
The lead time was 143 days against a plan of 131, a variance of 12. The goods became sellable on Thursday 28 October — 17 days after the planned sellable date and 10 after the in-store date. The other five days came from the PO leaving on Monday 7 June, five days late, when costing closed late:
| Segment | Plan days | Actual days | Variance |
|---|---|---|---|
| Decision: buy approved to PO issued | 7 | 12 | +5 |
| Vendor: PO issued to ex-factory | 91 | 94 | +3 |
| Origin to port: ex-factory to arrival | 31 | 37 | +6 |
| Destination: arrival to sellable | 9 | 12 | +3 |
| Lead time: PO issued to sellable | 131 | 143 | +12 |
| Slip against planned sellable: decision + lead time | — | — | +17 |
| Buffer held before the in-store date | 7 | — | −7 |
| Days late against the in-store date | — | — | +10 |
The vendor’s segment grew three days: fabric ran two long, a second PP sample round cost three and a failed final inspection three more, less two recovered at cutting, one in production and two at handover. Yet the goods left the factory eight days late, five of them the late PO. The origin leg grew six days with no slow transit: cargo handed over on Thursday 9 September missed the Wednesday cutoff for the Saturday 11 September sailing and took the next one, on the 18th — an 8-day slip at ex-factory became 14 days at departure. A customs examination and an extra day at the DC added the last three.
The receipt plan counted 140 of intake in week 12; it arrived in week 13. Month three still receives 290 and closes on its 580 target, so a monthly grid shows no variance — week 12 traded without the stock, and the delivery lost ten planned selling days. Four more days of slip would have moved the 140 into month four: receipts of 390 instead of 250, and an opening stock-to-sales ratio of 440 ÷ 340 = 1.29 against the planned 580 ÷ 340 = 1.71. The WSSI shows the week-12 hole; the reforecast re-solves a slip that crosses a month.
Lead time vs cycle time vs on-time delivery
Lead time
How long from commitment to goods sellable?
A duration between two named events, waits included: 143 days from PO issued to sellable on the worked delivery, and 94 for the vendor’s part, PO issued to ex-factory.
Cycle time
How long did the work take once it started?
One process from the moment work starts to the moment it ends, without the queue in front of it: cut started to production complete took 27 days against 28 planned. The 67 days between the vendor’s 94-day lead time and that cycle time are approvals, materials and waiting — the part that shortens without anyone sewing faster.
On-time delivery (OTD)
Did it arrive by the committed date?
A date test, not a duration: on time or late for one delivery, and on-time deliveries ÷ total deliveries × 100 across a period. The worked delivery was 8 days late at ex-factory and 10 days late against its in-store date.
A vendor can run a long, stable lead time and deliver on time every time, or quote a short one and miss it. OTD rewards predictability and lead time rewards speed: a short lead time lets a decision wait for sell-through, and a reliable one lets the buffer be small. Score OTD against the original committed date rather than a re-confirmed one, say whether it is measured at ex-factory or in-store, and remove the brand’s decision lag before charging a vendor — five of the eight days here. The vendor scorecard template holds the per-delivery record.
Measuring variability and turning it into a buffer
A planning figure needs a set of like-for-like deliveries — same vendor, product type, lane and mode, and new or repeat. Before the week-12 delivery, this lane’s seven ran 126, 128, 130, 131, 133, 135 and 138 days from PO to sellable; the plan used the vendor-based 131 plus 7 days, covering the longest. The week-12 delivery, at 143, became the eighth.
| Planning figure | Days, PO to sellable | Later than it, of 8 |
|---|---|---|
| Vendor-based plan | 131 | 4 |
| Mean of the eight | 133.0 | 3 |
| Plan plus the 7-day buffer | 138 | 1 |
| Mean plus one standard deviation (5.6) | 138.6 | 1 |
| Longest observed | 143 | 0 |
The eight have a mean of 133.0, a median of 132, a range of 17 days and a standard deviation of 5.6. Planning at the average accepts that some deliveries land after it: three of the eight ran past 133 days and four past the vendor-based 131. The 7-day buffer and the mean plus one standard deviation, 138.6, each covered seven; covering all eight takes 143, a 12-day buffer carried on every delivery for the one that ran long.
Lead-time error is lopsided: goods cannot ship before they are made, and an early handover still waits for its sailing, while lateness has no ceiling — so the buffer protects the late side only. Splitting deliveries by segment shows where the spread sits; on the week-12 delivery it was an approval round and the sailing step, addressed by an earlier fit sign-off and a handover date set against the cutoff.
For a seasonal delivery the buffer is days on the calendar; for a replenished style it is units on the shelf. At an illustrative 140 units a week, 20 a day, the five days from the mean to the seven-of-eight figure cost 100 units and the ten days to the longest cost 200; one standard deviation, 5.6 days, is about 112 units. That is the lead-time half of a safety stock — demand variability is the other half, and safety stock for seasonal assortments covers where the textbook formula breaks.
Back-scheduling from the in-store date with a T&A calendar
A forward projection asks when an order placed today will be sellable. A backward schedule asks the question the receipt plan needs: for goods to be sellable in the week the plan put them, what is the latest date each milestone can happen? Start at the in-store date, subtract the buffer, then each segment in reverse. The week-12 delivery, as planned:
| Milestone, working back | Days to the step above | Latest date |
|---|---|---|
| In-store date: week-12 intake | — | Mon 18 Oct |
| Sellable | 7 (buffer) | Mon 11 Oct |
| Received at DC | 3 | Fri 8 Oct |
| Customs released | 3 | Tue 5 Oct |
| Arrived at destination port | 3 | Sat 2 Oct |
| Vessel departed | 28 | Sat 4 Sep |
| Ex-factory: booking cutoff | 3 | Wed 1 Sep |
| Final inspection passed | 5 | Fri 27 Aug |
| Production complete | 2 | Wed 25 Aug |
| Cut started | 28 | Wed 28 Jul |
| PP sample approved | 5 | Fri 23 Jul |
| Bulk fabric in-house | 9 | Wed 14 Jul |
| Lab dips and trims approved | 28 | Wed 16 Jun |
| PO issued | 14 | Wed 2 Jun |
| Buy approved | 7 | Wed 26 May |
Read from the bottom, the table is the delivery’s T&A calendar, with a latest date and an owner for every milestone. Read from the top, it tests feasibility: 145 days from buy approval to the in-store date, so on this lane a buy approved after 26 May could not make week 12 without shortening a segment — an air leg, held fabric, a pre-approved trim package.
Anchor on the sellable date, never a ship date. Schedule timetabled legs by the timetable: the latest ex-factory date is the booking cutoff for the sailing that makes the arrival date, which is why the table puts ex-factory on Wednesday 1 September for a Saturday 4 September departure. And re-project forward from actuals every week, because the gap to the in-store date is the early warning. The T&A calendar guide covers milestones and owners, the T&A calendar template holds the schedule, and the production WIP tracker template carries the actual dates.
The free T&A calendar template runs this back-schedule. Enter the in-store date in its anchor cell and give each milestone the days to the next one down — the middle column of the table above — and every planned date back-calculates from the anchor, so a changed lead time re-dates that milestone and every one before it.
Hold the buffer as the lead time on the row directly above the in-store date: sellable, 7 days, for the week-12 delivery. Where a leg runs to a timetable, overwrite its planned date with the booking cutoff; planned dates stay editable, and the milestones before it re-date from the new date. The template pre-loads twelve apparel milestones from line freeze to in-store, so rename them and set their lead times to your own critical path, then enter actual dates weekly — the variance column, actual minus planned, shows the milestone where a slip starts.
How lead time sets the chase window, the reorder point and the OTB reserve
Open-to-buy is committed on the PO date and received on the sellable date, so a receipt month is spent one lead time earlier. The week-12 PO left on 7 June, 56 days before week 1 traded: that delivery’s share of month three’s open-to-buy was committed eight weeks before any sell-through existed. The longer the lead time, the more of a season is committed on no in-season data.
The chase window is the same subtraction: the latest chase PO is the first markdown date, less the full-price weeks a chase needs, less the chase lead time. A style on the shared season with its first markdown at the start of week 18, four full-price weeks needed, and two reorder routes:
| Line | Reorder on held fabric | Reorder on new fabric |
|---|---|---|
| First markdown: start of week | 18 | 18 |
| Full-price weeks the chase needs | 4 | 4 |
| Latest sellable: start of week | 14 | 14 |
| Chase lead time, PO to sellable (weeks) | 8 | 13 |
| Latest chase PO: start of week | 6 | 1 |
| Weeks of sell-through read before the PO | 5 | 0 |
On held fabric the last chase PO is the start of week 6, after five weeks of sell-through; on new fabric it is week 1, so the reorder is a second initial buy. The reorder route’s lead time decides whether a chase is possible, which makes held fabric or reserved capacity a pre-season decision. The reserve follows: an illustrative 60 of month four’s 250 held against the 8-week route is spendable until week 6, while held against the 13-week route it can only be spent blind and starves the front of the season. The receipt-flow guide sizes the reserve, and the reforecast guide places the chase among the other levers.
For a replenished style, stock on hand plus on order has to cover demand over the lead time and the review period, plus the buffer. An illustrative core style selling 140 units a week, planned at six weeks from PO to sellable and reviewed weekly, needs 140 × (6 + 1) = 980 units; covering ten days of overrun at 20 a day adds 200, for a reorder point of 1,180. A week off the lead time takes 140 units off the reorder point with no change in cover. The replenishment program guide covers min/max and pack rounding.
What drives lead time in each vertical
The subtraction is identical everywhere. What changes is which segment carries the length, which carries the variability, and what the end event really is. Apparel is the reference case. No day counts are given: without a vendor, a lane and a product, a day count is not a fact about a vertical.
Apparel
Fabric is the long segment: a developed or dyed-to-order fabric sets the cut date, and stock-supported or greige-held fabric shortens lead time more than faster sewing can. Approvals are the variable part — lab dips, strike-offs, fit rounds and the PP sample are each round trips — and trims from nominated suppliers gate the cut as surely as fabric. Carry-over styles on approved materials skip most approvals; children’s apparel adds pre-shipment safety testing.
Footwear
Tooling comes first: a new last or outsole mold is a development segment that a repeat style on existing tooling skips. Production covers the full size run — every size, half size and width, with molds per size — so more widths tie up more tooling. Count pairs and measure the whole run: a delivery short of its core sizes is sellable in name only. Prebooks set quantities against the ship window the accounts booked.
Accessories
Hardware and leather set the length. Custom hardware needs tooling and plating, so a new finish is a development segment that a hero color on the evergreen core, reordered on existing hardware, skips. Leather adds hide sourcing, tanning and color matching, with minimums per colorway. The end date is borrowed: an accessory bought to attach to an apparel or footwear drop has to land with that drop.
Home and furniture
The container sets quantity and timing together: orders are built to container quantities, space is booked on a sailing, and waiting to fill or consolidate a container adds days before departure. Ocean lead times make transit the long segment, and freight charged on cube feeds landed cost. Special orders end at delivery to the customer — a promise made at the point of sale — and options and finishes produced per order add a segment stocked items skip.
Outdoor
Model years fix the end date: gear has to be sellable when its model year opens and the dealer ship window starts. Technical materials — membranes, insulation, coated fabrics — carry their own development and testing segments. Dealer prebooks firm up the quantity after the production slot is booked, and counter-seasonal snow and summer categories run different calendars through shared vendors.
Sporting goods
Team and season dates do not move. Team and roster orders add a decoration segment after the blank goods arrive, so lead time ends when the finished order ships, not at DC receipt. Model years and dealer prebooks work as they do in outdoor, and golf, ski, cycling and racquet each run their own ship window, so lead time is measured per category against it.
Beauty and wellness
Components set the fill date: formulas pass stability and compatibility testing, regulatory review covers ingredients, claims and labeling for each market, and bottles, pumps, closures and cartons come from separate suppliers with their own minimums — filling waits for the last one to arrive. Days in transit and at the DC consume shelf life (expiry dating), so a late delivery reaches retailer POS with less sellable life left, and launches land against retailer resets that do not move.
Toys and games
Safety testing is a pass-or-fail gate before shipment, and a failure means rework and a retest. Licensed product adds licensor approval of the product and its packaging, and Q4 concentration and retailer commitments fix the end date. Peak congestion is a variability mechanism: when importers ship for the same peak, vessel space and terminal capacity tighten together, so a buffer measured on off-peak deliveries understates the pre-Q4 lane.
Baby and juvenile
Certification gates hard goods: car seats, cribs and strollers are tested to their safety standards before they ship, and a change of component or material can require retesting — a cost saving that adds a segment. Model-year changeovers fix when the new model must be sellable, registry demand needs stock available when an item is added, and large cube makes the container booking a lead-time decision.
Jewelry and watches
Lead time runs per piece: casting, stone setting, finishing and, where a market requires it, hallmarking run in sequence with hand work, so capacity is counted in pieces. The gap between order and the date metal cost is fixed exposes the cost to metal price moves, and watches add movement sourcing and assembly. Memo and consignment goods are sellable somewhere else, so lead time to a selling floor can include a recall.
For container-based lines, check what transit and duty add to unit cost on the landed cost calculator; for a line whose volume lands in a few weeks, read how to plan a peak-concentrated season.
- Lead-time and OTD calculator →
- T&A calendar template →
- How to build a T&A calendar →
- How to plan receipt flow →
- How to read a WSSI →
- How to plan a replenishment program →
- Production WIP tracker template →
- Vendor scorecard template →
- Lead time — glossary →
- On-time delivery (OTD) — glossary →
- The time-and-action calendar in apparel on RetailNorthstar →
Frequently asked questions
- What is lead time?
- Lead time is the elapsed time between committing to an order and having the goods available to sell. For planning, measure it in calendar days from the PO issue date to the date the units are received, checked and sellable. Definitions ending at ex-factory or DC receipt suit other owners, so compare only lead times measured between the same two events.
- How do you calculate lead time?
- Subtract the PO issue date from the sellable date. Date every milestone in between — approvals, materials, cut, production complete, inspection, ex-factory, departure, arrival, customs and DC receipt — so each segment is a subtraction and the segments sum to the total. In this guide’s illustrative delivery, a PO issued on 7 June 2027 and goods sellable on 28 October 2027 give a lead time of 143 days against a plan of 131.
- What is the difference between lead time, cycle time and on-time delivery?
- Lead time is the duration from commitment to goods sellable, waits included. Cycle time is the duration of one process from when work starts to when it ends, without the queue in front of it — cut to production complete, for example. On-time delivery is a date test: did a delivery arrive by its committed date; across a period it is on-time deliveries ÷ total deliveries × 100. A long, stable lead time can deliver perfect OTD.
- Should lead time be measured to ex-factory, DC receipt or the in-store date?
- Record all three. PO to ex-factory is the vendor’s segment and belongs on its scorecard. PO to sellable is the planning lead time, because a receipt counts in the week stock can sell. The in-store date is the target rather than an end event: the plan holds a buffer before it, and OTD against it tests the whole chain.
- How do you turn lead-time variability into a buffer?
- Group completed deliveries by vendor, product type, lane and mode, and read the range, the standard deviation and how many ran past the plan figure. Choose the figure to plan to — in this guide’s illustration, 138 days covered seven of eight deliveries against a vendor-based 131. Hold the difference as calendar days for a seasonal delivery, or as units, overrun days times daily sales, for a replenished style.
- How does lead time affect open-to-buy and chase decisions?
- Open-to-buy is committed on the PO date and received on the sellable date, so a longer lead time commits more of the season before sell-through exists. The latest chase PO is the first markdown date, less the full-price weeks a chase needs, less the chase lead time: a markdown at week 18, four weeks and an 8-week route give week 6. Size an open-to-buy reserve by what short-lead routes can deliver inside that window.
See how RetailNorthstar keeps purchase orders, production milestones and the receipt plan on one shared data model — so a slipped milestone is visible against the receipt week and open-to-buy it feeds.