Release lead time: why the average lies to you
“Our average release lead time is fifteen days.” Yet supply chain chases urgent batches every week, and nobody can give a reliable date for a given batch. The problem isn’t the average. It’s everything it hides.
1. Look at the spread, not just the average
An average of fifteen days can mean batches all released between thirteen and seventeen days, or most released in eight days with a few batches waiting forty. For supply chain and for customers, these are completely different situations.
The box plot is the simplest tool for seeing this reality: the median, the middle half of the batches, and the extremes. It answers the real question: what lead time can we promise, and for what proportion of batches? The goal isn’t just to reduce the average lead time, but to tighten the box, so that lead time becomes predictable.
2. Stick to first in, first out
When priorities change with every chaser, “urgent” batches overtake the others. The overtaken batches age, become urgent in turn, and overtake the next ones. It’s a vicious circle: the more you prioritise case by case, the more unpredictable the flow becomes, and the more emergencies there are.
Handling batches in order of arrival, except for genuinely justified exceptions, seems counter-intuitive. Yet it’s what makes lead time predictable for everyone, and makes most emergencies disappear.
3. Find the bottleneck, and manage at its pace
A release flow goes through several steps: record review by production, review by quality assurance, quality control results, deviation handling, certification. The throughput of the whole is set by the slowest step: the bottleneck. Speeding up the other steps achieves nothing; batches simply pile up in front of it.
The bottleneck isn’t always the same. It can move from one week to the next, depending on absences, volumes or open deviations. Hence the importance of weekly visual management, which shows where batches are waiting and lets you put resources in the right place.
What you can gain
By working on these three levers, one site cut its release lead time from 46 to 34 days in one month. Elsewhere, record review went from two days to three hours. Most of the time, what’s missing isn’t extra people, but a clear view of the flow.
Where to start?
- Extract the key dates of your latest batches and draw a box plot, step by step.
- Identify where batches wait the longest: that’s your current bottleneck.
- Set up a short weekly check-in around a visual board of the flow.
