HKSM

Duration estimates quantify the time needed to complete activities with the planned resources, expressed in calendar units. They can be single-point values or ranges and should state assumptions and confidence levels.

Key Points

• Duration reflects calendar time, not effort hours; resource availability and calendars matter.
• Common techniques include expert judgment, analogous, parametric, three-point (PERT), and bottom-up estimating.
• Estimates can be deterministic (single value) or probabilistic (range with confidence).
• Risks, constraints, and resource productivity strongly influence duration outcomes.
• Documenting the basis of estimate, assumptions, and data sources improves credibility.
• Reserve (contingency) is planned for known-unknowns; avoid hidden padding.

Purpose of Analysis

To forecast how long activities and the overall schedule will take so the team can build a realistic plan, identify the critical path, and set stakeholder expectations. Duration estimates support resource planning, cost forecasts, risk responses, and schedule commitments.

Method Steps

• Confirm the activity list and required deliverables are clear and complete.
• Identify assigned resources, their skills, availability, and productivity rates.
• Select estimating approach(es): analogous, parametric, expert judgment, bottom-up, or three-point.
• Estimate each activity’s duration considering scope, methods, resource limits, and calendars.
• For three-point, capture optimistic, most likely, and pessimistic values and compute expected duration and range.
• Factor in known risks, dependencies, and constraints; determine needed contingency reserve.
• Review estimates with the team, compare to historical data, and document the basis of estimate.
• Update the schedule model and analyze the impact on the critical path and milestones.

Inputs Needed

• Defined activities with descriptions, assumptions, and dependencies.
• Resource plan, resource calendars, and availability constraints.
• Productivity rates, performance data, and organizational metrics.
• Historical information and lessons learned from similar work.
• Risk register entries that may affect time (threats and opportunities).
• Project constraints, policies, and external factors such as mandated dates.

Outputs Produced

• Activity duration estimates (single-point or ranges with confidence).
• Basis of estimates, including methods used, data sources, and assumptions.
• Identified reserve needs (contingency and, if applicable, management reserve).
• Updates to the schedule model, activity attributes, and risk register.

Interpretation Tips

• Ranges communicate uncertainty; a narrow range suggests higher confidence than a wide one.
• Check how estimates affect the critical path and near-critical paths.
• Differentiate effort from duration; multiple resources do not always reduce duration linearly.
• Validate estimates against benchmarks or past projects to spot optimism bias.
• Ensure reserves are visible and justified rather than hidden in activity padding.

Example

Using three-point estimating for an activity: optimistic 4 days, most likely 6 days, pessimistic 10 days. The expected duration is (4 + 4×6 + 10) ÷ 6 = 6.3 days, with a range of 4–10 days. You record the basis: two experienced team members, historical data from a similar task, and one risk that could add up to 2 days if triggered.

For a parametric example: installing 50 identical units at 0.5 hours each with one technician available 7 productive hours per day yields expected duration ≈ (50 × 0.5) ÷ 7 ≈ 3.6 working days, before considering risks and setup time.

Pitfalls

• Confusing effort hours with calendar duration.
• Ignoring resource availability and team calendars.
• Providing single-point estimates where risk is high and uncertainty is known.
• Omitting the basis of estimate, making later review and negotiation difficult.
• Double-counting reserve or hiding padding inside activity estimates.
• Assuming perfect productivity and no interruptions (optimism bias).

PMP Example Question

A team estimates an activity at 120 hours of effort. One full-time resource can provide 6 productive hours per day. What is the most realistic duration for the activity?

1. 15 working days
2. 20 working days
3. 10 working days
4. 24 working days

Correct Answer: B — 20 working days

Explanation: Duration is effort divided by productive hours per day: 120 ÷ 6 = 20. Duration reflects calendar time with resource productivity, not effort alone.