When managing a project, determining how long each activity will take is crucial for developing an accurate schedule. But estimating activity durations isn’t as simple as just guessing. It requires carefully analyzing the work involved, resources available, and project constraints.
Whether you’re a Project Manager or project team member, understanding activity duration estimation helps you plan and execute projects successfully. This process involves various techniques from expert judgment to three-point estimating.
By learning when and how to apply these techniques, you can estimate realistic activity durations which allows you to meet deadlines, satisfy stakeholders, and keep your project on track.
This article will explore the key concepts and methods around estimating activity durations in project management.
What is the Estimate Activity Durations Process About?
The Estimate Activity Duration process focuses on analyzing each activity in a project to determine how long it will take to complete. An activity is a specific task that must be performed to create a project deliverable. The time required depends on the scope of work, assigned resources, activity relationships, and other constraints.
Estimating activity duration accurately relies on using specific tools and techniques to make reasonable time forecasts. The resulting duration estimates allow the project manager to develop the schedule and understand the feasibility of meeting deadlines. Accurate estimates also help determine project costs and measure performance against a baseline.
Continuous refinement of duration estimates is key as a project evolves and more details become known. While an early estimate might be rough, the methodology provides a scalable approach for progressive elaboration of the schedule.
What Are Activity Duration Estimates?
Activity duration estimates refer to the expected time required to complete project activities. They represent the total work periods needed to deliver each activity, measured in hours, days, weeks, or months.
For example, if a project involves developing a new website, some key activities could include:
- Conduct user research on desired features
- Create sitemaps and wireframes
- Write website content
- Develop page templates
- Build site pages and functionality
- Test website and fix bugs
- Deploy live site
The Project Manager would estimate how long each of these activities will take based on the scope of work involved. Accurate estimates depend on understanding the resources available, their skills and availability calendars, activity relationships, and other project constraints.
Estimating techniques like expert judgment, analogous estimating, or three-point estimating help forecast realistic activity durations. These estimates may be refined throughout the project life cycle as more details emerge.
Reliable activity duration estimates allow you to develop an achievable schedule, validate team capabilities, inform stakeholders, and more accurately estimate project costs. They are a fundamental input for successful project planning and execution.
What is the Basis of (Duration) Estimates?
The basis of estimates explains the methodology and assumptions behind activity duration forecasts.
Documenting your estimation basis is crucial for maintaining consistency across a project and facilitating updates when factors change. The basis should cover:
- Estimation techniques used
- Description of data sources
- Assumptions made
- Any constraints or risks considered
- Range of possible outcomes
- Level of confidence in the duration estimates
A strong basis puts estimates in context, provides justification, and allows for refinement over time. For example, an early estimate of 10 days for testing may get updated to 15 days once the scope of features is finalized.
By tracking your estimation basis, you enable continuous improvement in predicting activity durations throughout and across projects. Maintaining this estimate documentation is a best practice that builds stakeholder confidence in your schedules.
Importance of Activity Duration Estimates
Accurate activity duration estimates are vital for project success. Key benefits include:
- Developing the Schedule: Duration estimates enable the creation of a realistic schedule. By sequencing and scheduling activities, you can meet deadlines.
- Validating Team Capabilities: The aggregated estimates act as a litmus test for your team’s ability to deliver within given constraints. You can then adjust resources based on activity time forecasts.
- Communicating Plans: Sharing activity estimates with stakeholders sets aligned expectations around timelines and demonstrates diligent planning.
- Monitoring Progress: You can compare actual performances vs estimates to track project performance. Where there are significant deviations, then that’s a signal for the need for intervention.
- Estimating Project Costs: Since certain resources are costed per hour, activity durations help estimate the overall project budget.
- Establishing a Baseline: Duration estimates provide a baseline to assess if the project is on track or slipping.
- Identifying Risks: Estimating reveals risks like resource bottlenecks. You can build contingencies into the schedule.
- Optimizing Efficiency: Analyzing duration drivers helps find ways to accelerate activities, like adding resources or improving processes.
Estimate Activity Durations Process Activities
The estimate activity durations process involves core steps to forecast the time needed for each activity. Key activities include:
- Determine Level of Accuracy Needed: Consider how precise your estimates must be at this stage. Early phases may allow rough estimates, while execution needs more precision.
- Review Activity Attributes: Gather details like activity scope, required resource types, projected start and finish dates, predecessors, and sequence.
- Choose Estimating Technique(s): Select technique(s) like analogous, parametric, or three-point estimating based on data available, time, and accuracy needed.
- Identify Assumptions: Note assumptions that underpin the duration estimate, like resource productivity, workdays per week, or process efficiencies.
- Estimate Duration: Apply selected technique(s) to forecast the time needed for each activity.
- Document Estimation Basis: Record data sources, assumptions, ranges, and confidence to justify the estimate.
- Develop Activity Schedule: Sequence activities and determine project time span. Assess feasibility relative to milestones and constraints.
- Refine as Needed: Progressively elaborate estimates as more details emerge through project execution.
Estimate Activity Durations Inputs
The PMBOK Guide lists key inputs for estimating accurate activity durations:
- Activity List: These are the activities that define the work involved requiring duration estimates.
- Activity Attributes: Details like activity predecessors, resource needs, and start/end dates.
- Resource Calendars: Working days and non-working days for resources tied to activities.
- Risk Register: Risks that may impact activity durations, like staff turnover or technical hurdles.
- Activity Cost Estimates: Budget factors that may constrain durations, like fixed hourly rates.
- Project Scope Statement: Deliverables, assumptions, and constraints that frame the work effort.
- Organizational Process Assets: Policies, past project data, and lessons learned that inform estimates.
Estimate Activity Durations Tools and Techniques
The PMBOK Guide likewise outlines several tools and techniques to forecast activity durations. Choosing the right approach or combination of approaches depends on the project lifecycle stage, availability of data, time constraints, required accuracy, and other factors. These include:
1. Expert Judgment
This entails leveraging subject matter experts (SMEs) with historical experience performing similar activities to provide duration estimates based on their expertise.
The SMEs should be able to explain their full rationale including assumptions, prior examples, and data that informs their recommendation. Also, consider potential biases based on any unjustified optimism or oversights on their part.
Supplement expert input with detailed metrics from previous comparable projects where available. This technique is heavily dependent on the reliability, due diligence, and objectivity of the experts.
2. Analogous Estimating
Analogous estimating uses actual durations from a comparable past activity as the basis for estimating the current activity duration.
However, ensure the historical reference project has very significant similarities to the current project in terms of scope, complexity, team composition, tools/techniques used, operational environment, etc. to make the analogy truly meaningful.
For example, if a prior project took 5 days to develop user acceptance testing scenarios for a 50-page requirements document, you could estimate 5 days for UAT scenario development in the current project for a 60-page requirements document, adjusting upward or downward as necessary for any differences.
This technique can be quite helpful when you have completed very similar work before, but accuracy depends heavily on the close applicability of the reference data. Document all details of the analogous project and clearly justify any duration adjustments made.
3. Parametric Estimating
Parametric estimating uses a mathematical model that multiplies the quantity of work by a productivity factor to calculate duration.
For example, Duration = Number of Features to be Tested / Average Testing Productivity per Day.
Such models should be developed based on a sizable dataset of historical projects (e.g. >30 projects) to ensure statistical significance of the productivity metrics. Continuously refine the productivities over time by calibrating them with data from each new completed project.
This technique can provide calculated data-driven estimates, but relies heavily on having valid productivity metrics that translate accurately and appropriately to the current project’s parameters. The models must be carefully calibrated and refreshed regularly to remain relevant over time.
3. Three-Point Estimating
Three-point estimating technique develops an optimistic, most likely, and pessimistic duration estimate for each activity. Then uses a weighted average formula such as:
Estimated Duration = (Optimistic Duration + 4 x Most Likely Duration + Pessimistic Duration) / 6.
The optimistic estimate represents the minimum time required in ideal conditions, while the pessimistic reflects the maximum duration given potential issues arising. This helps account for the uncertainty inherent in estimating.
However, it can be time-consuming to create multiple estimates per activity. Document the underlying assumptions and rationale used to develop the three scenarios. Accuracy is still dependent on the rigor, objectivity, and care put into creating the three estimates.
4. Group Decision-Making Techniques
This entails leveraging group techniques like brainstorming, Wideband Delphi technique, and nominal group technique to gather input from a diverse set of experts or team members.
This is useful for reaching consensus from different perspectives, provided the sessions are facilitated effectively by an experienced moderator. Outcomes depend heavily on the group dynamics and mitigation of biases.
The rotation of participants in each round can increase objectivity. Also, actively challenge any groupthink by encouraging dissenting perspectives and playing devil’s advocate.
Have participants independently estimate durations before the group session to avoid anchoring bias, and document all individual estimates for future reference and calibration.
5. Reserves Analysis
This technique assesses all known risks to determine contingency reserves that may be required to account for estimated activity delays or obstacles.
For example, adding 2 extra days to the testing timeline to account for critical bugs that may be found in preceding development work. This helps pad the project schedule with safety buffers as appropriate.
However, risk identification can be challenging and reserves may still prove to be insufficient if new risks emerge over the course of the project. As a starting point, have SMEs estimate the reserve impact of any ‘known unknowns’.
6. Data Analysis
Data analysis reviews detailed historical data from a sufficiently large sample of comparable completed projects to inform the activity duration estimates. For example, evaluating metrics like average actual time per test case in prior projects.
This provides data-driven estimates, but depends heavily on the availability of reliable, directly applicable historical data matching the current project parameters. It’s important to assess data cleanliness and consistency before use.
7. Project Management Software
This involves using tools like Gantt charts, critical path analysis, scheduling/timing analysis, Monte Carlo simulations, and resource leveling capabilities to model, analyze, and refine preliminary activity duration estimates.
This requires developed skills in the specific software used. While these software automate some of the analytical aspects of estimating, they should however be used to supplement rather than replace the other techniques where possible.
Estimate Activity Durations Outputs
The key outputs from estimating activity durations include:
- Activity Duration Estimates: This is the time duration forecasted for each activity using chosen techniques. For clarity, the basis of estimates should be documented.
- Activity Attributes Updates: Any changes to activity attributes like dependencies or resource requirements stemming from duration analysis.
- Project Schedule: An initial high-level schedule depicting sequenced activities with start/finish dates based on estimated durations.
- Project Documents Updates: Updates to documents like the schedule baseline, activity list, and assumptions log based on new estimates.
- Lessons Learned: Insights gathered during estimation to improve the accuracy of future estimations.
Activity Durations Estimate Example
Consider a project to deploy a new call center technology solution. In this scenario, the Project Manager needs to estimate the duration of key activities like:
- Configure Hardware: Setup the servers, computers, headsets, and other devices needed for the call center.
- Develop Training Materials: Create user manuals, quick reference guides, presentations, and demos to train call center staff on using the new system.
- Validate Requirements: Review requirements with stakeholders to finalize them for development.
- Customize Software: Modify the vendor platform based on configured requirements for the organization.
- User Acceptance Testing: Have call center teams test the customized solution.
The PM starts by reviewing historical data from prior call center deployments to gather inputs on activity durations. She also interviews call center staff to determine resource factors that may impact the timeline.
Considering these considerations, the PM chooses to leverage analogous estimating for activities performed before and three-point estimating for new activities. She develops an initial optimistic, pessimistic, and most likely duration estimate for each task.
Using the data collected and selected techniques, the PM forecasts the duration of each activity and will refine the estimates as needed as the project progresses.
Conclusion
Accurately estimating activity durations is a core project management skill that improves your ability to develop realistic schedules and plans. You have your pick of techniques to do this, like analogous or 3-point estimating based on your context.
Leverage inputs like past data, expert judgment, and software tools to forecast task timelines, and refine estimates as the project progresses. Honing your estimating approach takes practice but is vital for project success.
Effective activity duration estimating helps you manage scope, resources, risks, and quality. So make this an essential part of your PM toolkit.
