Lean teams use JIT because excess inventory hides problems and ties up cash and space. Lowering inventory exposes issues like unreliable machines or long changeovers. JIT depends on stable processes, so it is usually paired with TPM, SMED and standard work.
Where it comes from
Just-in-time is one of the two pillars of the Toyota Production System. Taiichi Ohno developed it at Toyota, drawing partly on how supermarkets restock shelves as customers take goods.
At a glance
Push compared with pull
Swipe sideways to see the whole diagram.
How to apply Just-in-Time
- 1
Map the value stream
Draw the current flow of material and information. Mark where inventory piles up and where work is pushed by schedules.
- 2
Set the pace with takt time
Calculate takt time from customer demand. Use it to size the flow and spot steps that cannot keep up.
- 3
Create continuous flow where possible
Link process steps so work moves one piece or small batch at a time. Remove waiting and transport between steps.
- 4
Use pull where flow is not possible
Place supermarkets and kanban between steps that cannot be linked directly. Upstream steps replenish only what downstream has used.
- 5
Level the schedule
Use heijunka to smooth the mix and volume released to the line. A level schedule keeps pull signals steady.
- 6
Lower inventory and fix what appears
Reduce buffers step by step. Each problem that surfaces becomes a target for kaizen before the next reduction.
Worked example
A furniture plant builds frames in large weekly batches that sit before upholstery. It adds a small supermarket and kanban cards so frames are made only when upholstery pulls them. Work in process drops, and a recurring frame defect is now caught within a day.
Common mistakes
- Cutting inventory before equipment and suppliers are reliable, which causes shortages.
- Pushing inventory onto suppliers and calling it JIT.
- Using pull signals without leveling demand, so upstream steps swing between idle and overloaded.
When Just-in-Time is not the right tool
Just-in-time leaves little buffer, so it is exposed to supply disruption. Where supply is unreliable or lead times are long, planned buffers may be the sensible choice.
It also needs stable processes. Frequent breakdowns or long changeovers make small batches hard to run.
JIT inventory
JIT inventory means holding only the materials needed for current demand and receiving them close to when they are used. Instead of large stocks bought on a forecast, materials are replenished in small quantities as they are consumed.
Low inventory frees cash and space, and it exposes problems that stock used to hide, such as unreliable suppliers or long changeovers. That is also the risk: without stable processes and suppliers, a JIT system stops when something goes wrong.
Push vs pull
In a push system, each step makes products according to a schedule and pushes them to the next step, whether or not that step is ready. In a pull system, each step makes only what the next step has used, signaled by kanban.
JIT relies on pull. The pull system page covers how to set one up, including supermarkets and FIFO lanes between steps.
JIT at Toyota
Just in time is one of the two pillars of the Toyota Production System; jidoka is the other. Kiichiro Toyoda used the phrase in the 1930s, and Taiichi Ohno built the working system of kanban and pull at Toyota after the war.
Origins
Toyota credits Kiichiro Toyoda with the just-in-time idea, and Taiichi Ohno with developing it into a working system.
Ohno's book on the Toyota Production System describes how supermarket restocking inspired parts of the pull system.
What needs to be in place first
Common prerequisites are reliable equipment through TPM, short changeovers through SMED and clear standard work.
Kanban then carries the pull signals, and heijunka levels the load.
| Item | Push (forecast-driven) | Pull (just-in-time) |
|---|---|---|
| What starts work | A schedule or forecast | Actual use downstream |
| Inventory | Builds where the schedule runs ahead | Held in small, controlled stores |
| Typical tools | MRP schedules | Kanban, supermarkets, heijunka |