Free tool
Lead time calculator
Enter order and received dates from past purchase orders to get the mean lead time, its variability, and how it compares to what the supplier quoted.
Your purchase orders
Enter the order date and received date for each purchase order.
| Order date | Received date | Lead time | Remove |
|---|---|---|---|
| 10 d | |||
| 16 d | |||
| 14 d | |||
| 18 d | |||
| 11 d | |||
| 15 d |
Estimated mean lead time
14 days
- Sample standard deviation
- 3.03 days
- Minimum / maximum
- 10 / 18 days
- Average slip vs. quote
- +2 days
- Orders later than quoted
- 4 of 6 (66.67%)
This standard deviation is the lead-time variability the safety-stock calculator asks for: a wider spread needs more safety stock to hold the same service level, even at the same average lead time.
The formula
Lead time = received date − order date, in calendar or business days
Mean = SUM(lead time) ÷ n
Sample standard deviation = SQRT(SUM((lead time − mean)^2) ÷ (n − 1))
Average slip = mean − quoted lead time
- Lead time
- APICS/ASCM defines lead time as the elapsed time from order placement to receipt of the goods, available for use: order preparation, the supplier's own production or pick lead time, transit, and receiving/inspection all sit inside that one span. This calculator measures the whole span, order date to receipt date, not any single component of it.
- Order date
- The date the purchase order was placed with the supplier.
- Received date
- The date the goods were received and available for use, not the date they shipped. Measuring to ship date understates true lead time by the transit leg.
- n
- The number of purchase orders in the sample.
- Sample standard deviation
- The spread of lead times around the mean, using n − 1 in the denominator because the sample mean is itself estimated from the same data. Undefined with fewer than two orders. This is the figure that feeds a safety-stock calculation: more variability needs more safety stock to hold the same service level, even at an unchanged average lead time.
- Quoted lead time
- The lead time the supplier quoted, entered here for comparison. Optional. Without it, this calculator still reports the measured mean and spread, just not the slip or late share.
Worked example
- Six purchase orders give six lead times, order date to received date: 10, 16, 14, 18, 11, 15 days. The mean is their sum ÷ 6 = 14 days.
- Each lead time's deviation from that mean, squared: 16, 4, 0, 16, 9, 1, sum to 46. Dividing by n − 1 = 5 gives 9.2, and the square root is the sample standard deviation, 3.03 days.
- Against a 12-day quote, the average slip is 14 − 12 = +2 days.
- 4 of the 6 orders (66.67%) ran longer than the quoted 12 days. That spread, not the average, is what a safety-stock calculation needs.
When it applies
- Setting or checking a supplier's real lead time and its variability from several recent purchase orders on the same route, rather than trusting a quoted figure.
- Feeding a mean and a standard deviation into a safety-stock or reorder-point calculation.
- Projecting an expected arrival date for a specific order once a lead time (measured or quoted) is known.
When it breaks down
- Mixing purchase orders from different suppliers, shipping modes, or origin ports in one sample: the resulting mean describes a blend that no single future order will actually experience.
- A supplier that has recently changed its process, moved factories, or switched carriers: older receipts no longer describe current performance and should be dropped from the sample.
- Too few orders: with one purchase order there is a lead time but no variability, and with two or three the sample standard deviation is unstable.
Common mistakes
Using the supplier's quoted lead time instead of measured receipts
A quote is a target, not a measurement. This calculator treats quoted lead time as a comparison figure only. The mean, spread, min and max all come from actual order and received dates.
Ignoring variability because the average looks fine
Variability, not the mean, is what drives safety stock. A supplier that averages the quoted lead time but swings widely around it needs more safety stock than one that runs a day or two slower but consistently.
Measuring to ship date instead of receipt date
ASCM lead time ends when goods are available for use, not when they leave the supplier's dock. Measuring to ship date drops the transit leg and understates the true lead time.
Questions
What is lead time in supply chain?
Lead time is the elapsed time from placing an order to having the goods received and available for use. It bundles order preparation, the supplier's own production or pick time, transit, and receiving/inspection into one span, measured from the buyer's order date to the buyer's receipt date.
Why is lead time variability important?
Safety stock exists to cover demand and supply uncertainty during the lead time, and lead-time variability (its standard deviation) is one of the two inputs that determine how much is needed, alongside demand variability. Two suppliers with the same average lead time can require very different amounts of safety stock if one is far less consistent than the other.
What is the difference between lead time and cycle time?
Lead time is the buyer-facing span from order to receipt. Cycle time is a production or process measure: the time to complete one unit or one cycle of a process step, often used inside manufacturing rather than across the order-to-receipt boundary. A supplier's cycle time is one component that rolls up into the lead time a buyer experiences.
Does lead time include shipping?
Yes, under the standard ASCM definition: lead time runs from order placement to receipt, and transit time sits inside that span. A lead time quoted without shipping (sometimes called production lead time or ex-works lead time) is a narrower figure and should be labeled as such when compared against a door-to-door number.
Is lead time and delivery time the same?
They are usually used to mean the same order-to-receipt span, but "delivery time" is sometimes used more narrowly for the transit leg alone. Check which one a specific source means before combining or comparing figures from different systems.
Related
Published by Skuvelo. Results are estimates computed from the figures you enter, not a reading of your own sales or stock.
A calculator answers once. Skuvelo keeps answering.
This tool computes one number from what you type. Skuvelo computes it continuously, for every SKU, from your own sales and stock.