Duration Estimates Project
PMBOK v8 Definition
Duration estimates are quantitative assessments of the likely number of time periods that are required to complete an activity, phase, or project. Duration estimates do not include any lags. Duration estimates may include some indication of the range of possible results.
Estimating effort and duration is about determining the number of work periods (hours, days, weeks, or other) needed to complete individual activities with estimated resources. This process uses information from the scope of work, required resource types or skill levels, estimated resource quantities, and resource calendars.
Why It Matters for the Exam
Duration estimates appear frequently in PMI exam questions related to Schedule Management, particularly in scenario-based questions where you must distinguish between effort and duration. Questions often test your understanding that duration estimates exclude lags and may include range indications, and that they are derived from scope, resources, and resource calendars.
Key Points to Remember (for the exam)
- Definition: Duration estimates are quantitative assessments of likely time periods required to complete an activity, phase, or project
- Exclusion: Duration estimates do NOT include any lags
- Range Indication: Duration estimates may include some indication of the range of possible results (e.g., ±10%)
- Work Periods: Estimating duration uses hours, days, weeks, or other work periods
- Key Inputs: Scope of work, required resource types/skill levels, estimated resource quantities, and resource calendars
- Common Confusion: Duration ≠ Effort; duration is calendar time, effort is person-hours
- Process Context: Estimating effort and duration provides the amount of time and effort each activity will take to complete
Typical PMI Exam Example
A project manager is estimating the duration for a software development activity. The team estimates the work will require 80 person-hours of effort. Two developers are available full-time (8 hours/day). What is the duration estimate for this activity? The answer is 5 work days (80 hours ÷ 2 resources ÷ 8 hours/day), assuming no lags.
PMI Exam Traps
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Trap: Confusing duration with effort
- Reality: Duration is calendar time periods; effort is person-hours of work
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Trap: Including lags in duration estimates
- Reality: Duration estimates explicitly exclude any lags
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Trap: Assuming duration estimates are single-point values
- Reality: Duration estimates may include a range of possible results
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Trap: Ignoring resource calendars when estimating duration
- Reality: Resource calendars are a key input to estimating duration
Important PMI Connections
| Related Concept | Relationship Type | Exam Attention Point |
|---|---|---|
| Development Approach | Influences estimation method | Predictive uses detailed estimates; adaptive uses relative sizing |
| Deliverable | Defines scope for estimation | Duration estimates are based on deliverables to be produced |
| Resource Calendars | Key Input | Determines availability that affects duration |
| Cost Forecasts | Related Output | Duration estimates feed into cost forecasts (EAC) |
Quick Review Questions
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What is the key difference between a duration estimate and effort estimate?
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Are lags included or excluded from duration estimates according to PMBOK v8?
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What three types of information from the scope and resources performance domains are used to estimate effort and duration?
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Can a duration estimate include a range of possible results? If so, what does this look like?
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How does the development approach (predictive vs. adaptive) affect how duration estimates are created?
PMBOK v8 Reference
Section 4.2 - Project Development Approaches Section 2.2 - Scope Performance Domain Section 2.6 - Resources Performance Domain Step 3: Estimate Effort and Duration