What Just-in-Time is
Just-in-Time (JIT) is one of the two pillars of the Toyota Production System, alongside Jidoka. The principle is to produce only the right part, in the right quantity, at the exact moment it's needed — not before, not after — eliminating intermediate inventory and the tied-up capital it represents.
The 3 elements of JIT
Takt Time
The rate at which the customer buys the product, calculated as available time ÷ demand. It's the "metronome" that sets the pace of the whole process.
Continuous Flow
Producing and moving one piece (or a small batch) at a time between stations, instead of accumulating large batches that sit idle.
Pull Production
Each step only produces when the downstream process signals a need, usually through Kanban.
Prerequisites for implementation
- Process stability: reliable equipment and standardized work (without it, JIT amplifies every instability)
- Fast changeovers (SMED): long setups make small batches impractical
- Quality at the source (Jidoka): without buffer stock, an undetected defect stops the entire line
- Reliable suppliers: frequent, on-time deliveries, often daily
JIT isn't about having zero inventory at any cost — it's about having exactly the inventory the flow needs to keep moving.
Risks and cautions
Implementing JIT without these prerequisites tends to cause line stoppages and delivery delays, because the system has no cushion to absorb variation. Companies that faced supply-chain disruptions in recent years have shifted to blending JIT with strategic safety stock for critical items, while keeping the principle for high-turn, low supply-risk parts.
Want to understand JIT's companion pillar?
Read about Jidoka: how to stop the line at the source of a defect without losing productivity.
Read the article
About the author
Lean Manufacturing & Behavioral Management Specialist
Over 20 years in the automotive and metalworking industries (GM and Dana), Lean Manufacturing practitioner since 2006. SENAI instructor and mentor in Brazil’s Brasil Mais Produtivo program, delivering consulting, training and audits for 50+ companies, combining quality, productivity and people development.