Demystifying Estimate Accuracy: What Actually Breaks Down, and Why It Persists

Why Estimate Classification Alone Does Not Guarantee Estimate Accuracy | ROMAN Consulting Group

Many capital projects assume that assigning the correct estimate class automatically defines estimate accuracy. In reality, estimate classification and estimate accuracy answer two different questions. Classification reflects the maturity of project scope and deliverables, while accuracy reflects the uncertainty remaining in the estimate based on quantified project risk. When these concepts are treated as interchangeable, organizations can develop false confidence in cost estimates and make investment decisions based on misleading assumptions.

Drawing on Martin Darley's 2026 AACE International paper, this article explores how estimate accuracy can break down across every stage of Front-End Loading (FEL), from Class 5 through Class 3 estimates. It highlights common issues such as overstated scope maturity, methodology mismatches, incomplete engineering deliverables, and underestimated indirect costs that can undermine estimate credibility long before construction begins.

As an example: a Class 3 label paired with a lower-maturity FEL score describes two different realities. When they diverge, as they often do at this class, the stated accuracy range no longer reflects the project's actual maturity.

Estimate Classification vs. Estimate Accuracy: Demonstrates how estimate classification reflects project definition maturity while estimate accuracy depends on quantified uncertainty, emphasizing that the two should never be used interchangeably.

The same credibility gap shows up differently at every stage: alternatives mismanaged at Class 5, methodology mismatched at Class 4, indirect costs miscounted at Class 3.

Where Estimate Accuracy Breaks Down: Illustrates common failure patterns across Class 5, Class 4, and Class 3 estimates, including alternative selection bias, methodology drift, incomplete engineering definition, and indirect cost estimation challenges.

The article explains why stronger estimate governance requires organizations to:

• Distinguish estimate classification from estimate accuracy

• Align estimate class with actual scope maturity and engineering deliverables

• Validate estimate accuracy through structured risk analysis rather than standard accuracy tables

• Recognize how indirect costs and incomplete project definition influence estimate reliability

• Strengthen front-end governance through independent estimate reviews and project maturity assessments

Rather than viewing estimate accuracy as a fixed percentage associated with an estimate class, the article encourages owners and project teams to treat it as the outcome of disciplined project definition, structured risk analysis, and transparent estimating practices that improve confidence in capital investment decisions.

At ROMAN Consulting Group, we help owners, developers, and EPC contractors strengthen estimate credibility through independent estimate reviews, Basis of Estimate (BoE) evaluations, Project Definition Rating Index (PDRI) assessments, and front-end estimating support. Our objective is to ensure estimate classifications reflect actual project maturity, estimate accuracy is supported by quantified uncertainty, and investment decisions are based on transparent, defensible cost information.

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