Purchasing & suppliers
Lead Time Variability
By the Supply Chain Manager team · Updated October 16, 2026
Lead time variability is how much a supplier's actual delivery times swing around their average, measured as the spread of past lead times.
Two suppliers can both average 10 days. One delivers in 9 to 11; the other in 5 to 20. The second needs far more safety stock, because you must plan for the late deliveries, not the average.
Measuring it needs only three dates per purchase order: when it was placed, when it was expected and when it arrived. With those, you can calculate both the average lead time and its spread for every supplier, and see whether late deliveries are random or concentrated on particular items or seasons.
How to calculate lead time variability
Lead Time Variability = Standard Deviation of actual lead times (days)
Lead time variability example
Illustrative numbers: supplier A's last receipts took 9, 10, 11, 10 and 10 days (standard deviation about 0.7). Supplier B's took 5, 18, 7, 20 and 10 days (standard deviation roughly 6). Both average 10 to 12 days, but B can be more than a week late with no warning.
Why lead time variability matters for distributors
Variability, more than the average, causes stockouts. Reducing it, by changing supplier, agreeing delivery windows or ordering earlier, often cuts safety stock more than any forecasting change.
Common lead time variability mistakes
- Using only the average lead time in safety stock calculations.
- Judging a supplier on a handful of receipts.
Examples on this page use made-up round numbers to show the calculation. They are not benchmarks or results from real businesses.