Calculate a three-point estimate from optimistic, pessimistic and most likely durations.
Project Management
Project Estimating with Three-Point, Parametric and Reference Class Forecasting
A technical course on estimating project duration and cost using three-point, parametric and reference class forecasting methods, and on correcting for optimism bias in estimates.
🗓️Duration5 training days
📚Content4 modules · 8 sessions
🎓On completionAccredited attendance certificate
About the programme
Course Overview
Most project estimates are wrong in the same direction: too optimistic, anchored on a single confident number, and disconnected from how similar work has actually performed before. This course treats estimating as a technical skill rather than a guess dressed up in a spreadsheet, working through three distinct methods and when each applies. Three-point estimating turns a single guess into a range built from optimistic, pessimistic and most likely scenarios. Parametric estimating uses a statistical relationship between a measurable driver, such as area or unit count, and cost or duration, so estimates scale properly as project size changes. Reference class forecasting sets the specifics of the current project aside altogether and starts from the outcomes of a class of similar past projects, directly correcting for the optimism bias that affects even experienced estimators. Sessions include worked calculations, not just formulas, and tackle the practical problem of presenting a range estimate to a sponsor who wants a single number. The result is an estimator who can select and apply the right method for a given project, and defend the resulting estimate under pressure to compress it.
Expected Learning Outcomes
Apply parametric estimating using a measurable cost or duration driver from past project data.
Build a reference class from comparable past projects and adjust it for known differences.
Identify optimism bias and strategic underestimation in an existing project estimate.
Present a range estimate to a sponsor without it being collapsed back into a single number.
Select the estimating method appropriate to the data available and the stage of the project.
Recalculate an estimate when new information changes the assumptions it was built on.
Who Should Attend
Project managers and schedulers responsible for producing duration and cost estimates.
Cost engineers and estimators working on capital, construction or engineering projects.
Project management office staff setting estimating standards across a portfolio.
Programme managers reviewing estimates submitted by project teams before funding approval.
Bid managers preparing cost and schedule estimates for competitive proposals.
Anyone who must defend a project estimate to a sponsor pushing for a lower number.
Course Modules
Select any module to see its sessions and points.
01Three-Point Estimating
2 sessions · 8 points
Session 1Building a Three-Point Estimate
- Gather optimistic, pessimistic and most likely duration estimates for a specific task.
- Calculate an expected duration using the standard three-point weighted average formula.
- Estimate the standard deviation of a task to express how much confidence the estimate deserves.
- Distinguish genuine uncertainty from a task owner's reluctance to commit to a number.
Session 2Aggregating Three-Point Estimates Across a Schedule
- Combine three-point estimates across a sequence of tasks to estimate overall project duration.
- Identify which tasks contribute most to overall schedule uncertainty and deserve closer attention.
- Express an aggregated schedule estimate as a range rather than a single finish date.
- Explain why simply adding most-likely durations understates total schedule risk.
02Parametric Estimating
2 sessions · 8 points
Session 1Building a Parametric Model
- Identify a measurable driver, such as area, volume or unit count, that correlates with cost.
- Derive a cost or duration rate per unit from historical project data.
- Apply a parametric model to a new project and sense-check the result against experience.
- Recognise when a parametric model no longer fits because project characteristics have changed.
Session 2Validating and Adjusting Parametric Estimates
- Test a parametric estimate against at least one independent estimating method.
- Adjust a parametric rate for factors the model does not capture, such as site access or complexity.
- Maintain a database of historical rates so parametric estimates improve on future projects.
- Communicate the assumptions behind a parametric estimate so reviewers can challenge them properly.
03Reference Class Forecasting and Bias
2 sessions · 8 points
Session 1Building a Reference Class Forecast
- Select a reference class of genuinely comparable past projects for the forecast.
- Extract the actual outcome distribution, including overruns, from the reference class.
- Position the current project within that distribution based on known similarities and differences.
- Produce an uplift or adjustment to the base estimate derived from the reference class.
Session 2Correcting for Optimism Bias and Strategic Misrepresentation
- Distinguish optimism bias from deliberate strategic underestimation in a submitted estimate.
- Identify the typical points in an estimate where optimism bias tends to concentrate.
- Apply a bias correction derived from reference class evidence rather than an arbitrary buffer.
- Challenge an estimate that has been revised downward without a corresponding change in scope.
04Presenting and Defending Estimates
2 sessions · 8 points
Session 1Communicating Range Estimates to Sponsors
- Present a range estimate with enough explanation that a sponsor understands what drives the range.
- Respond to pressure to quote a single number without abandoning the underlying range.
- Link contingency and reserve levels visibly back to the estimating method used.
- Document estimating assumptions so they can be revisited when the project is re-baselined.
Session 2Choosing and Combining Estimating Methods
- Match an estimating method to the amount and quality of data available at the time.
- Combine three-point, parametric and reference class results into a single justified estimate.
- Update an estimate through the project life cycle as actual data replaces early assumptions.
- Record estimating accuracy after completion to build the reference data for future projects.
What the participant receives
4 course modules
A structured syllabus
8 training sessions
across 5 days
32 detailed points
Applied, detailed content
Accredited attendance certificate
On completing the programme
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