Plan, Do, Check, Act (PDCA)

An iterative improvement cycle based on the scientific method, in which a hypothesis regarding process improvement is formulated, tested, evaluated, and either adopted or adjusted. The cycle is also known as the Deming cycle or the Deming wheel, named after W. Edwards Deming, who popularized the concept in Japan in the 1950s. Deming built upon the earlier work of Walter Shewhart. The power of PDCA lies not in going through the steps once, but in continuously repeating them: each cycle builds upon the insights of the previous one.

The PDCA cycle consists of four stages:

Plan: Analyze the current situation, define the objective, and formulate a hypothesis: what change do we expect, and why? Also determine how the results will be measured.

Do: Implement the change, preferably on a small scale and in a controlled manner, so that the results can be reliably assessed.

Check: Compare the results with the expectations from the planning phase. Is the hypothesis correct? What has the change actually achieved?

Action: Implement the results. If the outcome is positive, adopt the change as standard practice. If not, use the insights gained as a starting point for a new cycle.

Within Lean , PDCA Lean the backbone of daily improvement and is closely linked to kaizen. Tools such as the A3 are essentially a structured application of the PDCA cycle.

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Toyota follows the PDCA framework but uses modified terminology in practice. The planning phase is preceded by an explicit step of understanding the situation, often referred to as “grasp the situation” or “go see” (see also: gemba walk). This emphasizes that no plan can be made without first understanding the actual situation on the shop floor. This aligns with the broader Toyota principle of genchi genbutsu: go there and see for yourself before drawing conclusions or making decisions.

A real-world example

A production team notices that a specific part regularly causes quality issues. In the Plan phase, the team formulates a hypothesis: the cause lies in a machine setting that is not consistently checked. In the Do phase, the team tests this hypothesis by adding an extra inspection step for one week, on a small scale and for a single machine. In the Check phase, the number of rejection reports is found to have dropped significantly. In the Act phase, the inspection step is incorporated into the standardized work for all machines of that type, and the team moves on to identify the next opportunity for improvement.

Common Mistakes in PDCA

PDCA is often used as a one-time improvement project rather than an ongoing cycle, which means the Act phase is never truly completed. Another common mistake is skipping or oversimplifying the Check phase: results are not compared with the original hypothesis, leaving it unclear whether the change actually worked. Additionally, the Plan phase often lacks a clear hypothesis, causing the Do phase to turn into trial and error without a clear benchmark.

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