Little's Law for your task list: why more in progress means everything takes longer

There is a small piece of mathematics that explains a lot of everyday frustration at work. It is called Little's Law, after John Little, who published a proof of it in 1961. It comes from queueing theory, the study of lines, and it applies to supermarket checkouts, factories and, it turns out, your task list.

What it says

For a stable system, on average:

Work in progress = throughput × time in the system

Rearranged:

Time to finish an item = work in progress ÷ throughput

In plain words: if you finish things at a steady rate, the more things you have in progress at once, the longer each one takes to finish.

A simple example

Say you finish about five actions a week.

• With 5 actions in progress, each one takes about a week from start to finish.
• With 20 actions in progress, each one takes about four weeks.

You are not working any slower. You are just spreading the same effort across more things, so each one waits longer for its turn.

Why this feels wrong

Starting something feels like progress. Having twenty things "in progress" feels busy and productive. But from the point of view of anyone waiting for one of those things, a client, a colleague, your future self, starting it changed nothing. Only finishing does.

What it means for teams

Teams fall into the same trap. Ten projects in progress for a team that can really push three at a time means every project takes three times longer than it needs to. Stakeholders see everything moving slowly and nothing finishing.

The two levers

Little's Law gives you two ways to get things done faster:

1. Increase throughput: finish more per week. Hard. Usually means more people, better tools or fewer interruptions.
2. Reduce work in progress: start fewer things at once. Easy to say, surprisingly effective.

The second lever is almost always the cheaper one. This is the reasoning behind Kanban's work-in-progress limits. See personal WIP limits.

A caveat about waiting

Not everything "in progress" is being worked on. Much of it is waiting on someone else. Waiting items still count as work in the system, and they are often the biggest reason things take long. Making waiting visible is the first step to reducing it. See the waiting-on-someone problem.

How a 2D board makes it visible

On an Axtio board, the Mine column is what you are actively doing and the Other column is what is waiting on others. Count each. If Mine is long, you are starting too much. If Other is long and old, your work is stuck in handoffs. Both are Little's Law, showing up in the shape of your board. See bottleneck thinking for projects.

For the original result, Little's 1961 paper "A Proof for the Queuing Formula: L = λW" appeared in the journal Operations Research.