Duration Estimating Worksheet
Calculate activity durations using parametric, analogous, and three-point (PERT) estimating techniques to build a realistic schedule baseline.
In this resource
§1 Purpose of the Estimating Worksheet
This worksheet documents the mathematical and historical basis for your schedule duration estimates, providing transparency into how timelines are calculated.
Project managers rarely rely on a single estimating method. Instead, they apply different techniques depending on the nature of the work and the historical data available. By documenting the exact parameters, multipliers, and PERT weightings used, the PM defends the schedule against arbitrary cuts and ensures the estimates can be independently validated.
- Parametric: Statistical scaling (e.g., 4 hours per page × 10 pages).
- Analogous: Historical comparison (e.g., "The last server migration took 5 days").
- Three-Point (PERT): Weighted average of Optimistic, Pessimistic, and Most Likely outcomes to manage high-uncertainty tasks.
§2 Blank Template
A structured format to break down the calculations for each estimating method.
DURATION ESTIMATING WORKSHEET
This worksheet documents the basis of duration estimates for the project. Three estimating techniques are used: parametric, analogous, and three-point (PERT).
Parametric Estimates
Formula: Duration = Effort ÷ (Resources × Hours/day × %Available × Performance Factor).
| ID | Effort Hours | Resource Quantity | % Available | Performance Factor | Duration Estimate |
|---|---|---|---|---|---|
| [ID] | [Hrs] | [Role/Count] | [%] | [1.0] | [Days] |
Analogous Estimates
Used when reliable history exists. Multiplier accounts for differences in scope, complexity, or team size.
| ID | Previous Activity | Previous Duration | Current Activity | Multiplier | Duration Estimate |
|---|---|---|---|---|---|
| [ID] | [Historical Task] | [Days] | [Current Task] | [1.0] | [Days] |
Three-Point (PERT) Estimates
PERT (beta) weighting: tE = (O + 4M + P) / 6. Used for activities with significant uncertainty.
| ID | Optimistic (O) | Most Likely (M) | Pessimistic (P) | Equation | Expected Duration |
|---|---|---|---|---|---|
| [ID] | [Days] | [Days] | [Days] | (O + 4M + P) / 6 | [Days] |
§3 Worked Example: Mary's Consulting
A completed example demonstrating how a PM calculates and justifies duration timelines across a mix of highly predictable and highly uncertain tasks.
DURATION ESTIMATING WORKSHEET
This worksheet documents the basis of duration estimates for the project. Three estimating techniques are used: parametric, analogous, and three-point (PERT).
Parametric Estimates
Formula: Duration = Effort ÷ (Resources × Hours/day × %Available × Performance Factor).
| ID | Effort Hours | Resource Quantity | % Available | Performance Factor | Duration Estimate |
|---|---|---|---|---|---|
| A006 | 30 hrs | 1 PM | 75% | 1.0 | 5 days |
| A014 | 100 hrs | 1 writer | 70% | 1.0 | 18 days |
| A016 | 60 hrs | 1 writer | 30% (waiting) | 0.5 | 25 days |
Analogous Estimates
Used when reliable history exists. Multiplier accounts for differences in scope, complexity, or team size.
| ID | Previous Activity | Previous Duration | Current Activity | Multiplier | Duration Estimate |
|---|---|---|---|---|---|
| A001 | Charter (prior internal project) | 5 days | Develop Project Charter | 1.0 | 5 days |
| A011 | Brand refresh (prior project) | 12 days | Develop Visual / Brand Design | 1.25 | 15 days |
| A039 | Prior site launch hypercare | 10 days | Post-Launch Hypercare | 1.0 | 10 days |
Three-Point (PERT) Estimates
PERT (beta) weighting: tE = (O + 4M + P) / 6. Used for activities with significant uncertainty.
| ID | Optimistic (O) | Most Likely (M) | Pessimistic (P) | Equation | Expected Duration |
|---|---|---|---|---|---|
| A009 | 3 | 5 | 9 | (O + 4M + P) / 6 | 5.3 → 5 days |
| A024 | 12 | 15 | 22 | (O + 4M + P) / 6 | 15.7 → 16 days |
| A032 | 5 | 8 | 14 | (O + 4M + P) / 6 | 8.5 → 8 days |
Fractional Availability
Observe A016 (Parametric). The writer only has 60 hours of active effort, but is waiting on 500+ consultants to reply. By setting "% Available" to 30%, the PM mathematically defends extending the duration to 25 days.
Multiplier Adjustment
In A011 (Analogous), the historical brand refresh took 12 days. However, the PM recognises the current project is more complex and applies a 1.25 multiplier to safely estimate 15 days.
PERT Weighting
The PERT formula uses a "Beta" distribution. By multiplying the Most Likely (M) estimate by 4, it heavily weights the average toward reality while still absorbing the outlier risk of the Pessimistic (P) scenario.