PDCA Cycle – Model for the Systematic Improvement of Processes

The PDCA cycle is a four-stage, iterative model for the systematic improvement of processes, products, and services. It comprises the phases Plan, Do, Check, and Act, which are run through continuously. Each cycle builds on the findings of the previous one, so the PDCA cycle describes not a one-time improvement step, but a recurring learning process.

Systemic Classification of the PDCA Cycle in Quality Management

In quality management, the PDCA cycle is anchored as a fundamental control model for process-oriented improvement. It forms a methodological framework for measures of quality assurance and can be combined with evaluations of statistical process control, for example when their results serve as the data basis for the Check phase. In ISO 9001, the PDCA cycle is explicitly named as the model behind the process approach of the standard.

Origin and Development of the PDCA Cycle

The foundations of the PDCA cycle go back to the American physicist and statistician Walter A. Shewhart, who worked on statistical quality control at Western Electric in the 1920s and 1930s. His original model comprised three steps and was published in 1939. William Edwards Deming, who knew and took up Shewhart’s work, extended the model to the four-stage form common today and disseminated it in Japan from the 1950s onwards.

Deming himself consistently spoke of the Shewhart cycle, as he attributed the original idea to Shewhart. In the technical literature and in general usage, the term Deming cycle has also become established. In Japan, the PDCA cycle contributed significantly to the spread of Kaizen and thus had a lasting influence on the development of modern quality management methods.

The Four Phases of the PDCA Cycle

The PDCA cycle is divided into four consecutive phases:

• Plan: analysis of the current situation, definition of objectives, and planning of the measures intended to achieve them
• Do: implementation of the planned measures, usually initially on a limited scale or under controlled conditions
• Check: verification of the results against the objectives defined in the Plan phase, including the evaluation of whether the expected effect has occurred
• Act: derivation of consequences from the verification – standardization of successful measures, adjustment in the event of deviation from the objective, or initiation of a new cycle

After completion of the Act phase, the cycle begins again, if necessary with adjusted objectives or on the basis of the findings gained in the meantime.

PDCA Cycle and Continuous Improvement Process (CIP)

The PDCA cycle must be distinguished from a continuous improvement process (CIP). CIP refers to the overarching organizational orientation of a company towards ongoing improvement as a principle. The PDCA cycle, by contrast, is a specific methodological tool with which this principle can be implemented in a structured way. A company can therefore pursue a CIP culture and use different methods in doing so, of which the PDCA cycle is one of the most widespread.

PDCA Cycle in ISO 9001

ISO 9001 names the PDCA cycle as the model underlying the process approach required by the standard. The standard itself does not prescribe any particular procedure for implementing the PDCA cycle, but requires that processes are planned, implemented, monitored, and improved where necessary. How a company organizes the PDCA cycle in concrete terms, for example at the level of individual processes, entire process chains, or the entire quality management system, is at the discretion of the organization.

Distinction of the PDCA Cycle from Other Improvement Methods

The PDCA cycle is occasionally equated with the PDSA cycle (Plan-Do-Study-Act). In later years, Deming preferred the term “Study” instead of “Check” in order to emphasize that the third phase is not limited to a mere target/actual comparison, but includes an in-depth evaluation of the findings gained. In terms of content, both terms describe the same basic model.

The PDCA cycle differs from DMAIC, the process model used in Six Sigma projects (Define, Measure, Analyze, Improve, Control), in its lower degree of formalization. DMAIC is designed for clearly delimited, mostly data-intensive improvement projects with a defined project completion, while the PDCA cycle, as a continuous, more broadly applicable basic model, is also suitable for smaller or more informal improvement steps.

Application of the PDCA Cycle in Manufacturing

In manufacturing, the PDCA cycle is used in various contexts, for example when introducing new inspection procedures, handling complaints, or implementing actions from internal audits. The cycle provides the structural basis, but does not replace the content-related methodology of the respective task, such as a root cause analysis or a risk assessment. The effectiveness of a measure implemented within the PDCA cycle must be demonstrated in the Check phase by suitable criteria; the PDCA cycle itself does not automatically ensure this evidence.

FAQ – Frequently Asked Questions About the PDCA Cycle

What is the objective of the PDCA cycle?

The objective of the PDCA cycle is the systematic and recurring improvement of processes, products, or services through the structured completion of the phases Plan, Do, Check, and Act.

Where does the PDCA cycle come from?

The PDCA cycle goes back to a three-stage model by Walter A. Shewhart from the 1930s, which William Edwards Deming extended to the four-stage form common today and disseminated in Japan from the 1950s onwards.

What is the difference between the PDCA cycle and the Deming cycle?

They are the same model under different names. Deming himself spoke of the Shewhart cycle, while the term Deming cycle has also become established in the technical literature.

Is the PDCA cycle part of ISO 9001?

ISO 9001 names the PDCA cycle as the model behind the process approach required by the standard, but does not prescribe any particular procedure for its implementation.

What is the difference between the PDCA cycle and DMAIC?

DMAIC is a more formal, mostly data-intensive process model for delimited Six Sigma projects with a defined project completion. The PDCA cycle, by contrast, is a continuous, more broadly applicable basic model with a lower degree of formalization.

Is the PDCA cycle a one-time procedure?

No. The PDCA cycle is designed as a recurring process: after the Act phase, the cycle begins again, if necessary with adjusted objectives.

What is the difference between PDCA and PDSA?

PDCA (Plan-Do-Check-Act) and PDSA (Plan-Do-Study-Act) refer to the same basic model. Deming preferred the term “Study” to emphasize the in-depth evaluation in the third phase as opposed to a mere target/actual comparison.

Standards and Norms

There is no separate standard for the PDCA cycle itself. Instead, it is embedded as a model in other regulations: ISO 9001:2015 explicitly names the PDCA cycle in its introduction as the basis of the process approach required by the standard, without itself specifying a methodology for carrying it out. The full text of the standard is available for a fee via the official ISO catalog; the scope and abstract are freely accessible.

Further Internal Content

• Quality management as the overarching technical framework of the PDCA cycle
• Action management as the organizational framework for the Act phase
• Complaint management as a typical field of application of the PDCA cycle

AI-assisted · Editing and publication: Christian Sedlag · Last updated: 28 October 2026