ISO 21502:2020 Clause 7.6.2 Estimating activity durations

Project Management 15 Minutes

Before developing the schedule, the project manager should work with the project team to estimate the duration of the project’s activities. Future activities can be defined in less detail than immediate activities. As the project progresses and more information becomes available, activities can be further defined and detailed. Activity durations can represent a trade-off between schedule constraints and resource availability. Periodic re-estimates resulting in updated forecasting against the baseline schedule can also be necessary. Activity duration estimates should be reconsidered throughout the life of the project. Once the activities are baselined, change requests should be used. At the same time, new risks and other events impacting the project should be identified.

Estimating activity durations is a critical aspect of schedule management in project organization. Here are several techniques commonly used to estimate activity durations:

  1. Expert Judgment: Seek input from individuals or teams with expertise in the relevant domain or industry. Experts can provide valuable insights based on their knowledge and experience, helping to produce more accurate estimates of activity durations.
  2. Analogous Estimating: Use historical data from similar past projects as a basis for estimating activity durations in the current project. Analogous estimating involves identifying projects with similar characteristics, such as scope, complexity, and resource requirements, and using their actual durations as a reference for estimating durations in the current project.
  3. Parametric Estimating: Use statistical relationships or mathematical models to estimate activity durations based on relevant parameters. Parametric estimating involves analyzing historical data to identify patterns or correlations between project variables (e.g., size, complexity) and activity durations, then using these relationships to predict durations for similar activities in the current project.
  4. Three-Point Estimating: Estimate activity durations using three different estimates: optimistic, pessimistic, and most likely. Three-point estimating helps account for uncertainty and variability in activity durations by considering best-case, worst-case, and most likely scenarios. The estimates are then combined using techniques such as the PERT (Program Evaluation and Review Technique) formula to calculate a weighted average or expected duration.
  5. Bottom-Up Estimating: Decompose project activities into smaller, more manageable tasks and estimate the duration of each task. Bottom-up estimating involves estimating the duration of each task based on detailed knowledge of the work required, resource availability, and other relevant factors. The individual estimates are then aggregated to determine the total duration of the activity.
  6. Delphi Technique: Use a structured, iterative approach to gather input from multiple experts anonymously. In the Delphi technique, experts provide estimates independently, and the estimates are compiled, analyzed, and shared with the group for further refinement. This process continues until a consensus is reached on the estimated duration.
  7. Group Decision-Making Techniques: Use collaborative techniques such as brainstorming or facilitated workshops to involve project team members in estimating activity durations. Group decision-making techniques promote open communication, consensus building, and the exchange of diverse perspectives, leading to more accurate and reliable estimates.
  8. Reserve Analysis: Factor in contingency reserves or buffers to account for uncertainty and risk in activity durations. Reserve analysis involves setting aside additional time or resources to accommodate unforeseen delays, dependencies, or other factors that may impact activity durations. Contingency reserves can be allocated at the activity level, project level, or both, depending on the level of uncertainty and risk.

Using these estimation techniques, project organizations can develop more accurate and reliable estimates of activity durations, enabling them to create realistic and achievable project schedules. It’s important to involve relevant stakeholders, leverage historical data and expertise, and consider the unique characteristics and requirements of the project when estimating activity durations. Regular review and refinement of estimates throughout the project lifecycle are also essential to ensure that the schedule remains current and reflects project realities.

Before developing the schedule, the project manager should work with the project team to estimate the duration of the project’s activities.

Involving the project team in estimating the duration of project activities is crucial before developing the project schedule. Here’s why it’s essential and how the project manager can collaborate with the team in this process:

  1. Collective Expertise: The project team members possess valuable knowledge and insights about the tasks they will be performing. By involving them in the estimation process, the project manager can tap into their collective expertise to generate more accurate and reliable estimates of activity durations.
  2. Ownership and Buy-In: Involving the project team in the estimation process fosters a sense of ownership and buy-in among team members. When team members participate in estimating the duration of activities, they are more likely to be committed to achieving the project goals and meeting the established schedule.
  3. Improved Accuracy: The project team members are the ones who will be performing the tasks, so they have firsthand experience and understanding of the work involved. By collaborating with the team in estimating activity durations, the project manager can leverage this knowledge to generate more accurate and realistic estimates.
  4. Enhanced Communication and Collaboration: Involving the project team in the estimation process promotes open communication and collaboration. It provides an opportunity for team members to discuss and share their insights, concerns, and expectations regarding the duration of project activities, fostering a shared understanding of project requirements and constraints.
  5. Identification of Risks and Dependencies: Collaborative estimation allows the project team to identify potential risks, dependencies, and constraints that may impact activity durations. By discussing and analyzing these factors together, the team can develop more comprehensive estimates that account for various uncertainties and challenges.
  6. Building Trust and Confidence: Collaborating with the project team in the estimation process builds trust and confidence among team members. It demonstrates that their input and expertise are valued and respected, fostering a positive team culture and environment conducive to project success.

To involve the project team in estimating activity durations effectively, the project manager can:

  • Facilitate collaborative estimation sessions with the project team, where team members can share their insights and perspectives on the duration of project activities.
  • Provide clear guidelines and templates for estimating activity durations, ensuring consistency and standardization across the team.
  • Encourage active participation and contributions from all team members, fostering a collaborative and inclusive decision-making process.
  • Document and validate the estimates generated through team collaboration, ensuring that they are comprehensive, realistic, and aligned with project objectives.

By working closely with the project team to estimate activity durations, the project manager can leverage the team’s expertise and insights to develop a more accurate and achievable project schedule, setting the stage for project success.

Future activities can be defined in less detail than immediate activities.

In project management, future activities are often defined in less detail compared to immediate activities. Here’s why:

  1. Focus on Near-Term Activities: Immediate activities, typically those scheduled to occur in the near term, require detailed planning and definition because they are the next steps to be executed in the project. These activities often have more certainty and are more concrete in terms of scope, resources, and dependencies.
  2. Uncertainty in Future Activities: Future activities, on the other hand, may be further out of the project timeline and may be subject to greater uncertainty. As the project progresses, more information becomes available, allowing for better definition and planning of future activities. Attempting to define future activities in too much detail early on may lead to inaccuracies and the need for frequent revisions as the project evolves.
  3. Flexibility and Adaptability: Maintaining flexibility and adaptability in the project plan is important, especially for future activities where there may be greater uncertainty or changes in project requirements. Defining future activities in less detail allows for greater flexibility to adjust and refine plans as more information becomes available and as project conditions change.
  4. Resource Allocation: Immediate activities require more detailed resource planning and allocation since they are the next tasks to be executed. Future activities may have less certain resource requirements, making it more challenging to allocate resources accurately at an early stage of the project.
  5. Focus on Critical Path: Immediate activities are often critical to the project’s critical path, which is the longest sequence of dependent activities that determines the minimum duration of the project. Therefore, detailed planning and execution of immediate activities are essential to ensure that the project stays on schedule.

Overall, while immediate activities require detailed planning and definition, future activities can be defined in less detail initially to allow for flexibility, adaptability, and refinement as the project progresses. This approach helps project managers focus their efforts on the most critical and immediate tasks while maintaining the ability to adjust plans and allocate resources effectively as needed.

As the project progresses and more information becomes available, activities can be further defined and detailed.

As the project progresses and more information becomes available, it’s common practice to further define and detail activities. Here’s why this approach is beneficial:

  1. Improved Understanding: As the project unfolds, stakeholders gain a better understanding of project requirements, constraints, and dependencies. This enhanced understanding allows project managers and teams to refine and specify activities more precisely to align with project goals and objectives.
  2. Reduced Uncertainty: Initially, some project activities may be planned with a certain degree of uncertainty due to incomplete information or evolving requirements. As more information becomes available and uncertainties are clarified, activities can be refined and detailed to reduce ambiguity and ensure accurate execution.
  3. Optimized Resource Allocation: With a clearer understanding of project requirements and timelines, project managers can optimize resource allocation by aligning resources more closely with specific activities. Detailed activity definitions enable more accurate resource planning, ensuring that the right resources are available at the right time to support project execution.
  4. Enhanced Schedule Management: Detailed activity definitions facilitate more effective schedule management by providing clearer milestones and checkpoints for tracking progress. Project managers can monitor the completion of detailed activities more closely, identify potential bottlenecks or delays, and take proactive measures to keep the project on track.
  5. Improved Risk Management: Detailed activity definitions allow project managers to identify and address potential risks more effectively. By breaking down activities into smaller, more manageable tasks, project teams can identify risks at a more granular level and develop targeted mitigation strategies to address them.
  6. Increased Stakeholder Confidence: Clear and detailed activity definitions provide stakeholders with greater visibility into project progress and status. Stakeholders can have more confidence in project outcomes when they can see that activities are well-defined, progress is being tracked effectively, and potential risks are being managed proactively.

Overall, as the project progresses and more information becomes available, it’s important to continue refining and detailing activities to ensure accurate execution, optimize resource allocation, enhance schedule management, mitigate risks effectively, and maintain stakeholder confidence in project outcomes. This iterative approach to activity definition supports the successful delivery of the project on time, within budget, and to the required quality standards.

Activity durations can represent a trade-off between schedule constraints and resource availability.

Activity durations often represent a trade-off between schedule constraints and resource availability in project management. Here’s how this trade-off works:

  1. Schedule Constraints: Project schedules are typically driven by deadlines and milestones that must be met to achieve project objectives within a specified timeframe. These schedule constraints may be dictated by external factors such as client deadlines, contractual obligations, or regulatory requirements. Meeting these schedule constraints is essential for project success and may require activities to be completed within a certain timeframe.
  2. Resource Availability: On the other hand, the availability of resources, including personnel, equipment, and materials, plays a crucial role in determining activity durations. Limited availability of resources may impact the duration of activities, as tasks may need to be scheduled around resource availability constraints. For example, if a key team member is only available part-time or if critical equipment is in high demand, it may extend the duration of certain activities.

When determining activity durations, project managers must navigate this trade-off between schedule constraints and resource availability to develop a realistic and achievable project schedule. Here are some considerations:

  • Resource Leveling: Project managers may employ resource levelling techniques to optimize resource utilization and minimize conflicts. Resource levelling involves adjusting the project schedule to smooth resource demand and avoid overallocation or underutilization of resources. This may entail extending the duration of certain activities to accommodate resource constraints while still meeting project deadlines.
  • Critical Path Analysis: Identifying the critical path, which represents the longest sequence of dependent activities in the project, can help project managers prioritize activities and allocate resources effectively. Activities on the critical path have zero slack and must be completed on time to prevent delays in the project schedule. By focusing resources on critical path activities, project managers can ensure that schedule constraints are met while maximizing resource efficiency.

Periodic re-estimates resulting in updated forecasting against the baseline schedule can also be necessary.

Periodic re-estimates resulting in updated forecasting against the baseline schedule are often necessary in project management. Here’s why:

  1. Changes in Project Scope: As the project progresses, there may be changes in project scope due to evolving requirements, stakeholder feedback, or external factors. These changes can impact the duration and sequencing of activities, necessitating re-estimates to update the baseline schedule and ensure it remains aligned with the current scope of work.
  2. Uncertainty and Risk Management: Projects are inherently subject to uncertainty and risk, which can impact the accuracy of initial estimates and forecasts. Periodic re-estimates allow project managers to incorporate new information, assess risks, and adjust forecasts accordingly to mitigate potential schedule deviations and uncertainties.
  3. Resource Availability: Changes in resource availability, such as fluctuations in personnel availability or unexpected constraints on equipment or materials, may necessitate adjustments to activity durations and resource allocations. Periodic re-estimates enable project managers to reassess resource requirements and reallocate resources as needed to optimize project performance.
  4. Performance Measurement and Control: Regular monitoring and measurement of project performance against the baseline schedule provide insights into actual progress and deviations from the plan. Periodic re-estimates help update forecasting against the baseline schedule, allowing project managers to identify trends, variances, and potential issues early and take corrective actions to keep the project on track.
  5. Continuous Improvement: Periodic re-estimates support a culture of continuous improvement in project management. By periodically reviewing and updating forecasts against the baseline schedule, project managers can learn from past experiences, identify areas for improvement, and refine estimation techniques and processes to enhance future project planning and execution.
  6. Stakeholder Communication: Regular updates to forecasting against the baseline schedule enable project managers to communicate transparently with stakeholders about project progress and potential impacts on schedule and delivery. This helps manage stakeholder expectations, build trust, and maintain alignment between project objectives and outcomes.

Overall, periodic re-estimates resulting in updated forecasting against the baseline schedule are essential for effective project management. They help ensure that project schedules remain realistic, achievable, and aligned with project objectives, allowing project managers to proactively manage risks, optimize resource utilization, and deliver successful outcomes.

Activity duration estimates should be reconsidered throughout the life of the project.

Reconsidering activity duration estimates throughout the life of the project is crucial for maintaining an accurate and realistic project schedule. Here’s why this iterative process is essential:

  1. Refinement of Estimates: As the project progresses and more information becomes available, activity duration estimates can be refined and adjusted based on actual performance data, lessons learned, and changes in project conditions. Reconsidering estimates allows project managers to incorporate new insights and adjust plans accordingly to reflect the current state of the project.
  2. Changes in Scope and Requirements: Project scope and requirements may evolve over time due to stakeholder feedback, changes in priorities, or external factors. Reconsidering activity duration estimates enables project managers to assess the impact of these changes on the project schedule and make necessary adjustments to accommodate new requirements while maintaining alignment with project objectives.
  3. Risk Management: Activity duration estimates are inherently uncertain and subject to risk. Reconsidering estimates throughout the project lifecycle allows project managers to identify and address risks that may impact activity durations, such as resource constraints, dependencies, or unforeseen challenges. By proactively managing risks, project managers can mitigate potential schedule deviations and ensure project success.
  4. Performance Monitoring and Control: Regular monitoring and measurement of project performance provide insights into actual progress and deviations from the planned schedule. Reconsidering activity duration estimates allows project managers to compare actual performance against initial estimates, identify variances, and take corrective actions to keep the project on track. By continuously evaluating and adjusting estimates, project managers can optimize project performance and minimize schedule risks.
  5. Continuous Improvement: Reconsidering activity duration estimates fosters a culture of continuous improvement in project management. By reflecting on past performance, analyzing deviations, and refining estimation techniques, project managers can enhance their ability to accurately predict and manage project schedules in future projects. This iterative process supports ongoing learning and improvement, driving better outcomes for the organization.

Overall, reconsidering activity duration estimates throughout the life of the project is essential for maintaining an accurate and realistic project schedule. By continuously evaluating and adjusting estimates based on evolving project conditions, project managers can effectively manage risks, optimize performance, and deliver successful outcomes.

Once the activities are baselined, change requests should be used.

Once activities are baselined, change requests become essential for managing any alterations or adjustments to the project scope, schedule, or resources. Here’s why change requests are crucial in this context:

  1. Formal Process: Change requests provide a formalized process for documenting, reviewing, and approving any proposed changes to the project baseline. This helps ensure that changes are carefully considered, evaluated for their impact, and approved by the appropriate stakeholders before implementation.
  2. Controlled Environment: By using change requests, project managers can maintain control over changes to the project baseline, preventing ad-hoc or unauthorized modifications that could disrupt project execution. Change requests establish a controlled environment for managing changes, helping to minimize scope creep and maintain project integrity.
  3. Documentation and Traceability: Change requests serve as a record of all proposed changes to the project baseline, including their rationale, impact assessment, and approval status. This documentation provides a clear audit trail, enabling project managers to track the history of changes and ensure transparency and accountability in change management processes.
  4. Impact Assessment: Change requests facilitate a systematic assessment of the impact of proposed changes on project scope, schedule, cost, quality, and other key parameters. By evaluating the potential consequences of changes, project managers can make informed decisions and prioritize changes based on their significance and alignment with project objectives.
  5. Stakeholder Involvement: Change requests involve relevant stakeholders in the change management process, ensuring that proposed changes are reviewed and approved by those impacted by or responsible for the project. This promotes collaboration, communication, and alignment among project stakeholders, fostering consensus and buy-in for approved changes.
  6. Change Control Board (CCB) Review: In many organizations, change requests are reviewed and evaluated by a Change Control Board (CCB) or similar governing body responsible for overseeing project changes. The CCB assesses change requests based on predefined criteria, such as their impact, urgency, and alignment with project objectives, and makes decisions on whether to approve, reject, or defer proposed changes.
  7. Risk Management: Change requests help mitigate risks associated with changes to the project baseline by ensuring that changes are carefully evaluated and controlled. By following a formal change management process, project managers can identify potential risks associated with proposed changes and implement appropriate mitigation strategies to address them.

Overall, change requests play a vital role in managing changes to the project baseline, providing a structured and controlled approach to evaluating, approving, and implementing alterations while minimizing disruption and maintaining project alignment with objectives.

At the same time, new risks and other events impacting the project should be identified.

Alongside managing change requests, it’s essential to continuously identify new risks and other events impacting the project. Here’s why this proactive approach is crucial:

  1. Risk Management: Identifying new risks allows the project team to assess potential threats to the project’s success and implement appropriate risk responses to mitigate their impact. By staying vigilant and proactive in identifying risks, project managers can prevent or minimize the likelihood and impact of adverse events on project objectives.
  2. Opportunity Management: In addition to threats, identifying new events also includes recognizing potential opportunities that may arise during the project lifecycle. These opportunities could include technological advancements, market trends, or changes in stakeholder needs that could positively impact project outcomes. By identifying and capitalizing on opportunities, project managers can enhance project success and deliver greater value to stakeholders.
  3. Change Management: New events may also trigger changes to the project scope, schedule, or resources, necessitating the submission of change requests. Identifying these events early allows project managers to assess their impact on the project baseline and initiate the appropriate change management processes to address them effectively.
  4. Stakeholder Communication: Identifying new risks and events provides valuable information that can be communicated to stakeholders, promoting transparency and awareness of potential project challenges and opportunities. Effective communication ensures that stakeholders are informed and engaged in decision-making processes, fostering trust and confidence in project management practices.
  5. Adaptation to Project Environment: Projects operate within dynamic and uncertain environments, where new risks and events may arise unexpectedly. Identifying and responding to these changes in the project environment allows project managers to adapt their strategies and plans accordingly, ensuring that the project remains resilient and capable of achieving its objectives despite external uncertainties.
  6. Continuous Improvement: Actively identifying new risks and events fosters a culture of continuous improvement in project management. By learning from past experiences and staying attuned to changes in the project environment, project managers can refine their risk management processes, enhance their ability to anticipate and address potential threats, and drive better project outcomes in future endeavours.

Overall, continuously identifying new risks and events impacting the project is essential for effective project management. By staying proactive and responsive to changes in the project environment, project managers can mitigate risks, capitalize on opportunities, adapt to evolving circumstances, and ultimately deliver successful project outcomes.

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Pretesh Biswas has wealth of qualifications and experience in providing results-oriented solutions for your system development, training or auditing needs. He has helped dozens of organizations in implementing effective management systems to a number of standards. He provide a unique blend of specialized knowledge, experience, tools and interactive skills to help you develop systems that not only get certified, but also contribute to the bottom line. He has taught literally hundreds of students over the past 5 years. He has experience in training at hundreds of organizations in several industry sectors. His training is unique in that which can be customized as to your management system and activities and deliver them at your facility. This greatly accelerates the learning curve and application of the knowledge acquired. He is now ex-Certification body lead auditor now working as consultancy auditor. He has performed hundreds of audits in several industry sectors. As consultancy auditor, he not just report findings, but provide value-added service in recommending appropriate solutions. Experience Consultancy: He has helped over 100 clients in a wide variety of industries achieve ISO 9001,14001,27001,20000, OHSAS 18001 and TS 16949 certification. Industries include automotive, metal stamping and screw machine, fabrication, machining, assembly, Forging electrostatic and chrome plating, heat-treating, coatings, glass, plastic and rubber products, electrical and electronic equipment, assemblies & components, batteries, computer hardware and software, printing, placement and Security help, warehousing and distribution, repair facilities, consumer credit counseling agencies, banks, call centers, etc. Training: He has delivered public and on-site quality management training to over 1000 students. Courses include ISO/TS -RAB approved Lead Auditor, Internal Auditing, Implementation, Documentation, as well as customized ISO/TS courses, PPAP, FMEA, APQP and Control Plans. Auditing: He has conducted over 100 third party registration and surveillance audits and dozens of gap, internal and pre-assessment audits to ISO/QS/TS Standards, in the manufacturing and service sectors. Other services: He has provided business planning, restructuring, asset management, systems and process streamlining services to a variety of manufacturing and service clients such as printing, plastics, automotive, transportation and custom brokerage, warehousing and distribution, electrical and electronics, trading, equipment leasing, etc. Education & professional certification: Pretesh Biswas has held IRCA certified Lead Auditor for ISO 9001,14001 and 27001. He holds a Bachelor of Engineering degree in Mechanical Engineering and is a MBA in Systems and Marketing. Prior to becoming a business consultant 6 years ago, he has worked in several portfolios such as Marketing, operations, production, Quality and customer care. He is also certified in Six Sigma Black belt .

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