Bathtub Curve

Definition of Bathtub Curve

The bathtub curve is a graphical representation used to illustrate the life cycle of a product or system, specifically its failure rates over time. It consists of three distinct phases: an initial period with a high but decreasing failure rate (infant mortality period), a steady state period with a relatively constant low failure rate (normal life period), and an increasing failure rate toward the end of its life (wear-out period). The curve resembles the shape of a bathtub, hence the name “bathtub curve.”


The phonetic pronunciation of the keyword ‘Bathtub Curve’ is: /ˈbæθtʌb ˈkɝ:v/

Key Takeaways

  1. The Bathtub Curve represents the failure rates of a system over time, illustrating three distinct phases: infant mortality, normal life, and wear-out.
  2. Infant mortality phase features a high, decreasing failure rate where issues arise due to design, manufacturing, or early usage faults. During the normal life phase, failures occur at a fairly constant, low rate. Finally, in the wear-out phase, failure rate increases as components reach the end of their useful life.
  3. Understanding and analyzing the Bathtub Curve is essential for effective system maintenance, planning, and quality control. This helps in identifying potential areas of improvement in design, manufacturing, and maintenance processes, ultimately prolonging the life of the system and reducing failures.

Importance of Bathtub Curve

The Bathtub Curve is an important concept in technology as it represents the failure rates of a product over time, illustrating the three distinct phases of a product’s life cycle: infant mortality, normal life, and wear-out phase.

Understanding the Bathtub Curve helps manufacturers and engineers to improve product design, predict and mitigate potential issues, enhance quality control, and optimize maintenance schedules.

By taking into account the distinct aspects of each phase, companies can extend the longevity and reliability of their products, leading to better user experiences, higher customer satisfaction, and reduced overall costs.


The Bathtub Curve is a widely recognized graphical representation used in the field of reliability engineering and life cycle management to illustrate the life stages of a product or a system. Its purpose is to predict and analyze failure rates over the life of a product or system, helping design engineers, quality teams, and manufacturers identify potential areas for improvement and anticipate maintenance needs.

This enables companies to develop more reliable products and systems, plan maintenance activities, and extend the overall service life expectancy, enhancing end-user satisfaction. The three distinct phases represented within the Bathtub Curve are the infant mortality phase (early failures), the normal life phase (random failures), and the wear-out phase (end-of-life failures). The infant mortality phase is characterized by rapid initial failures due to design, manufacturing, or material flaws.

As the product undergoes further testing and corrective actions are implemented, the failure rate decreases and transit smoothly into the normal life phase, which is characterized by a relatively constant, random failure rate. This is the phase where a product or system exhibits its highest level of reliability.

Finally, as products or systems reach their end of life, the wear-out phase begins, and failures increase again due to accumulated stress, wear and tear, and component degradation. Understanding these phases and monitoring performance against the Bathtub Curve allows companies to maximize product reliability, minimize costs, and meet end-user expectations.

Examples of Bathtub Curve

The bathtub curve is a concept used to represent the failure rates of products or systems over time. It’s called “bathtub curve” because its shape resembles the side view of a bathtub, with three distinct phases: an initial period of high failure rate (infant mortality), followed by a period of constant low failure rate (normal life), and finally an increasing failure rate (wear-out phase).

Electronics and gadgets: Consumer electronics, such as smartphones, tablets, and laptops, often follow the bathtub curve. Initially, there may be a higher rate of failures due to manufacturing defects or design issues. As these problems are addressed, the devices enter a period of stable operation with fewer failures. As they get older and components begin to wear out, users may experience an increased rate of failures, prompting replacement or repair.

Automobiles: Cars are another example where the bathtub curve can be applied. In the beginning, there may be some malfunctions or manufacturing flaws causing more failures. As the car is used over time, the failure rate stabilizes, and proper maintenance can help prolong this period. Eventually, as the car ages and components wear out, the failure rate increases due to mechanical issues or corrosion, necessitating repair or replacement.

Industrial machinery and equipment: Many machines used in factories and industrial settings also follow the bathtub curve. New equipment can experience an initial period of higher failures due to installation or manufacturing problems. Once these issues are resolved, the equipment moves into a phase of reliable operation, during which time it may require only regular maintenance. As the equipment ages, wear and tear, as well as technological obsolescence, lead to an increased rate of failures, and eventually, the need for replacement or refurbishment.

Bathtub Curve FAQ

1. What is the Bathtub Curve?

The Bathtub Curve is a common graphical representation of the lifecycle of various system components, typically representing product failure rates over time. It is composed of three distinct phases: an initial steep decline in failure rates (infant mortality), followed by a period of constant, relatively low failure rates (normal operation), and finally an increase in failure rates as the components reach the end of their useful life (wear-out).

2. What is the purpose of the Bathtub Curve in reliability engineering?

The purpose of the Bathtub Curve in reliability engineering is to provide a visual representation of a product’s failure rates over time, aiding engineers and system managers in understanding and predicting the performance of components during their lifecycle. It helps to identify potential problem areas and inform decisions regarding maintenance, replacement, and overall system reliability strategy.

3. How do you interpret the Bathtub Curve?

The three phases of the Bathtub Curve represent distinct periods in a component’s lifecycle. The initial steep decline in failure rates represents the ‘infant mortality’ phase, indicating that weaker components fail shortly after being placed into operation. The constant, low failure rate period represents the ‘normal operation’ phase, where properly functioning components exhibit a stable failure rate. Finally, the increasing failure rates towards the end of the component’s life represent the ‘wear-out’ phase, as components approach and surpass their expected service life.

4. How can the Bathtub Curve be used for preventive maintenance?

The Bathtub Curve can be used for preventive maintenance by identifying the ideal time to replace components or perform maintenance to minimize downtime and costs. By determining when a component is likely to enter the wear-out phase and experience increasing failure rates, preventive maintenance can be scheduled before the likelihood of failure becomes too high, thereby avoiding unplanned downtime and increasing the overall reliability of the system.

5. Are there any limitations to the application of the Bathtub Curve?

There are limitations to the application of the Bathtub Curve, as it may not accurately represent the failure characteristics of certain components or systems, particularly those with more complex failure modes. Additionally, the Bathtub Curve assumes constant operating conditions and may not account for environmental or usage factors that could impact component reliability. It can also be challenging to accurately estimate the timing of the wear-out phase for some products. Therefore, it’s essential to consider additional data and analyses when applying the Bathtub Curve in real-world situations.

Related Technology Terms

  • Reliability Engineering
  • Failure Rate
  • Infant Mortality
  • Wear-Out Phase
  • Normal Life Phase

Sources for More Information


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