Limiting WIP (work in progress) is another of those wonderfully simple Agile principles that many of us still struggle to implement and possibly understand the significance.

It’s fundamental to Lean/Kanban, and yet explaining it through Little’s Law is dull and abstract.. so here is my attempt to make it engaging and shareable.

Lead time (cycle time) is a measure of our responsiveness to change and closely correlated to customer perceptions of our team/organisation.

It’s clearly something we should be trying to reduce.

Lead time is a great empirical feedback loop:

  • Easy to measure – when did we start and when did we finish on a piece of work

  • Represents a system-level behaviours

  • Is ‘impossible’ to game or cheat

  • Easy to see trends over time. Are we becoming more or less responsive?

So…. what is the best way to reduce lead time (cycle time)?

Little’s law

This maths is robust and applies across all kinds of systems, from the queue at your coffee shop to the progress of a feature through your team.

It’s easier to visualise this as

If you want to half the lead time

– you only have two options

– and one is much quicker and cheaper than the other

This is probably our default response and it does work. However, it will take a lot of time and cost.

This is much quicker and cheaper to implement.

It is also the reason why Kanban obsesses about it – if you are not reducing your WIP to the optimum level, then you’re not doing Kanban

You can do either or both

..but the quickest, cheapest way to intervene at a system level and improve customer perceptions, responsiveness and innovation – is to reduce WIP