What Is a Basis of Estimate (BoE)? A Checklist for Capital Projects
Updated: 10 hours ago
Basis of Estimate (BoE) in Capital Projects | ROMAN Consulting Group
Why the Basis of Estimate Matters
A strong Basis of Estimate is the audit trail for your numbers. It clarifies scope and boundaries, shows how the estimate was built, records the data sources and dates behind it, and makes uncertainty visible so leaders can judge credibility.
A number without a BoE is really just a guess dressed up as an estimate.
Build the BoE in parallel with—or even ahead of—the estimate and write it so a reviewer who did not build the estimate can follow the logic.
AACE International Recommended Practice 34R-05 sets the standard: anyone with capital project experience should be able to understand and assess the estimate from the BoE alone.
The BoE also becomes the reference for change management after approval. The scope it records today is the scope every later change is measured against.
What Decision Makers Actually Need from a BoE
Replicable logic: another estimator can follow your steps and recreate the numbers.
Traceability: major assumptions and inputs are easy to find and linked to the WBS.
Currency: prices, labor bases, and indices carry a documented base date so updates are disciplined.
Separation of uncertainty: contingency and any management reserve are held separately.
Reconciliation: it is clear how and why the numbers changed since the last gate.
Five Habits That Lift BoE Quality from Complete to Decision Ready
1. Document assumptions clearly
Include the assumptions necessary for a knowledgeable reader to understand and, if needed, recreate the estimate. Where helpful, point to the WBS element the assumption influences.
Dollarizing is not required in the BoE. Record minor assumptions too, since RP 34R-05 notes that minor assumptions can become major ones over the life of a project.
Example of a traceable assumption entry:
A-07: Cooling water is supplied from the existing plant system, which has adequate spare capacity. No new cooling tower is included. (WBS: 300, Utilities)
2. Document the date basis and plan escalation
For each major commodity and labor basis, include the base date, any quote validity window, and the escalation index family you intend to use. Keep a short quote log in the BoE and put the detailed log in the backup.
This prevents quiet pricing drift and makes roll forwards consistent.
3. Show how the numbers moved
Use a simple waterfall from the prior estimate that isolates changes from:
Scope
Quantity changes
Quoted price or commodity updates
Wage rates and productivity refinements
Others
Place detailed trending in the attachments. Each line should point to the change log entry that explains it, so an approver can see where most of the movement came from.
4. Separate uncertainty tools cleanly
Risk mitigations: actions included in the estimate to reduce risk, inside the base cost.
Contingency: allowance for inherent variability within defined scope, inside the estimate, with the method stated.
Management reserve: funds for potential scope change, outside the estimate.
Labeling these avoids double counting and stops scope gaps from hiding inside contingency
5. Design for an independent read
Use the same code of accounts the estimate uses, define units and currency, and write plainly. If a reviewer cannot follow the BoE without tribal knowledge, approvals may be delayed.
This is also what makes an independent estimate review fast and useful. AACE describes the review process itself in RP 31R-03.
Basis of Estimate Guidance by FEL Stage
FEL 1 (Class 5): Assumptions carry the numbers
Keep it concise but explicit on boundaries, status of definition, and methods by area such as parametric and factored approaches.
A Class 5 BoE can need more documentation than one might think, because more of the numbers rests on assumptions.
Using PDRI can help structure definition.
Document the assumptions necessary for transparency and replication, and tie them to allowances or WBS elements where useful.
Record a pricing base date and the intended escalation approach to avoid false precision later.
For how early risk framing feeds the BoE, see When to Start Risk Analysis in Front End Loading.
FEL 2 (Class 4): Quantities and method take the lead
Shift from factors to traceable quantities and a dated quote log.
Explain how missing MTOs are bridged and when they will be replaced.
Develop a short complementary benchmark table such as unit costs or TIC per major block.
Keep a visible change log so approvers see what shifted since FEL 1 and why.
For a companion method that supports commercial leverage, see Should-Cost Estimating.
FEL 3 (Class 3): The BoE becomes the baseline
Attach an estimate deliverables checklist that compares the maturity each deliverable should have for the class with what was actually available. Asking the design team to state expected maturity before the estimate starts, then checking it at estimate time, shows the gaps early. A simple heat map makes them visible at a glance.
Summarize the execution assumptions the numbers depend on, such as contracting strategy, labor basis, modularization, and key schedule events.
Record and track the estimate reviews completed and any still planned before the funding decision.
Basis of Estimate Checklist
Boundaries
Purpose, decision context, and estimate class, with the reason for the class
Scope boundaries and what is out, aligned to the WBS
Exceptions: any deliverables normally required for the class that were not available
Methods
Methods, tools, codes, and data sources by area or discipline
Assumptions are documented clearly and easy to find
Quantity traceability, with gaps and allowances listed
Dates
Pricing sources with dates, escalation basis, and a quote log noted
Uncertainty
Risks, mitigations, contingency method and confidence, and management reserve are defined and separate
Change
Reconciliation waterfall to the prior estimate, with deeper trending attached
Estimate reviews completed to date and planned
Attachments
Full quote log, key references, risk notes, escalation calculations, and benchmarking
Common BoE Pitfalls with Fast Fixes
Two problems come up more than any others in the reviews I've been part of: a "Class 3" estimate that is really a Class 4, and a reconciliation that is either missing or buried in spreadsheets no one wants to open.
Implied scope not called out (owner's costs, utility tie-ins, or land) Fix: add an "items a reviewer might expect" list under Exclusions.
Expired quotes with without a plan Fix: add base dates and validity windows and state how you will roll forward, e.g., included in escalation.
Contingency hiding scope Fix: move unclear scope to assumptions or allowances and keep contingency for variability, not omissions.
No reconciliation to the prior baseline Fix: add the one-page waterfall and link to trending.
A class claimed without the deliverables to support it Fix: attach the deliverables checklist and list the exceptions.
Independent Basis of Estimate Reviews
At ROMAN Consulting Group, our work is independent and front end by design. Our aim is simple: reduce project cost uncertainty so leaders can make stronger investment decisions.
We provide independent estimating support and independent estimate reviews early, when a clear record of scope, methods, assumptions, and market basis can still shape choices. Our reviews are objective and practical, bringing structure and rigor to the front end of projects so owners move faster with fewer surprises.
Key Takeaways
A BoE should let someone who did not build the estimate follow and recreate it.
Document every pricing basis and show how the numbers moved since the last gate.
Keep mitigations, contingency, and management reserve separate and labeled.
Class 5 and Class 4 estimates often need a more thorough BoE than expected, because assumptions carry the numbers.
By FEL 3, the BoE becomes the baseline for change management and the funding decision.
Frequently Asked Questions
What is a Basis of Estimate in capital projects?
A Basis of Estimate is the documented foundation of a cost estimate that explains scope, methods, data and dates, key assumptions, risk and mitigations, and reconciliation to prior estimates. AACE International RP 34R-05 provides the standard structure.
What should a BoE include at FEL 1, FEL 2, and FEL 3?
At FEL 1, focus on boundaries, status of definition, and clear assumptions. At FEL 2, shift to traceable quantities, a dated quote log, benchmarking, and a visible change log. At FEL 3, add the deliverables checklist, execution assumptions, and a record of estimate reviews.
Do I need to quantify every assumption in the BoE?
No. Document assumptions clearly so a knowledgeable reader can understand and, if needed, recreate the estimate.
How do risk mitigations, contingency, and management reserve differ?
Risk mitigations are actions included in the base estimate to reduce risk. Contingency covers inherent variability within defined scope. Management reserve sits outside the estimate for potential scope change.
How often should a BoE be updated?
Update the BoE at each gate and whenever decisions change scope, quantities, pricing bases, or execution. Use a short reconciliation waterfall to show what moved and why.
Who should review a Basis of Estimate before a funding decision?
An experienced estimator who did not build the estimate, so the review tests the logic rather than repeating it. Many owners bring in an independent estimate reviewer at FEL gates, before funding approval.
Is an estimate complete without a Basis of Estimate?
No. Without a BoE, an estimate cannot be reviewed, defended, or reconciled at the next gate, however well the numbers themselves were built.
Reference
AACE International Recommended Practice No. 34R-05, Basis of Estimate, Rev. October 5, 2021.
Related AACE RPs: 18R-97 (estimate classification), 31R-03 (reviewing, validating, and documenting the estimate), and 110R-20 (estimate validation)
Reducing project cost uncertainty for stronger investment decisions.
Comments