Contingency Sizing: Why 5% of EPC Gives the Riskiest Project the Least Protection

Take two projects with identical $230m budgets. Project A has $190m of firm-priced EPC and $20m of interconnection under an executed agreement. Project B has $150m of EPC and $60m of interconnection still resting on a cluster study.

Apply an illustrative five-percent-of-EPC rule and A gets $9.5m while B gets $7.5m.

Run the worked assumptions used in this article and A's contingency sits at the P84 confidence level while B's sits at P55. Those percentiles are outputs of the assumed distributions and correlations; they are not market facts.

The convention gives the riskier project less money and a coin-flip level of protection, for exactly the reason that makes it riskier: its uncertainty is concentrated in a line the percentage is not applied to.

This post closes Project Finance Mechanics with a risk-driven contingency framework: use estimate maturity as one input, identify the risk drivers, model correlations and discrete events where relevant, and report what confidence level the carried contingency actually represents.

ℹ️ Note: All distributions and figures are labelled assumptions. The method is the point; the ranges should come from your own estimate classification and risk register.

What Is Contingency For?

A quantified allowance for uncertainty and risk within the scope and risk definition chosen for the estimate.

That wording matters because “contingency” is not one universal bucket. AACE's general principles say the client and practitioner should first agree what “risk” and “contingency” mean for the application, what decision the analysis supports, and what risk tolerance is being targeted.

The useful sequence is:

1. define the base estimate and scope;
2. identify the risk drivers;
3. distinguish inherent estimate uncertainty from project-specific risk events and systemic risks;
4. choose a fit-for-use quantification method;
5. select the confidence level or other decision output;
6. connect the contingency to the project's funding and cost-to-complete controls.

A flat percentage skips steps 2 through 5. It can still happen to land at a sensible number, but it does not tell the credit committee what protection that number actually buys.

What AACE Actually Says

AACE estimate classes are primarily classifications of project-definition maturity, not automatic contingency percentages.

AACE Recommended Practice 18R-97 provides example accuracy ranges for the process industries and explicitly says the ranges vary with project circumstances, technology, complexity, estimating quality, market conditions and other systemic risks. It also says the accuracy range should be determined through risk analysis of the specific project rather than pre-determined from the class.

That limitation matters for renewable project finance. RP 18R-97 expressly applies to process-industry EPC estimates and says it excludes power-generating facilities. Its table is therefore useful for understanding the concept of estimate maturity, but it should not be copied into a solar, wind or BESS financing as if AACE prescribed those percentages for power projects.

AACE RP 118R-21 is even more specific about the Monte Carlo method used in this article. Estimate-ranging Monte Carlo is recommended as a sole method only where scope is well-defined — Class 3 or better — with no new technology, minimal complexity and no significant project-specific risk events. Where those event risks or execution complexities matter, AACE recommends a hybrid or alternative risk-driven approach rather than line-item ranging alone.

AACE RP 40R-08 provides the higher-level rule: contingency estimating should be fit for use, should start with identifying risk drivers, and should link those risks to cost / schedule outcomes.

So the framework for this post is:

Estimate maturity            → informs inherent uncertainty
Risk register / event risks  → separate discrete-event analysis
Execution / technology risk  → systemic-risk treatment
Correlation                  → prevents false diversification
Target confidence            → management / lender risk tolerance

That is more work than multiplying EPC by 5%, but it is also what turns contingency into a credit decision rather than a convention.

The Problem With a Single Percentage

A financing budget contains lines with different contractual certainty and different risk drivers.

For the worked example below, assume — illustratively, not as AACE-prescribed ranges:

Line	Amount	Worked risk assumption	Illustrative upside
Firm-priced EPC scope	$190m	residual change-order / claim uncertainty	+6%
Owner-supplied equipment	$12m	procurement / logistics range	+20%
Interconnection / upgrades	$20m	immature estimate / allocation risk	+50%
Land, permitting, development	$8m	residual development uncertainty	+20%

A signed fixed-price EPC can narrow price uncertainty but does not eliminate scope change, claims, interface risk or contractor credit. An interconnection estimate may be far less mature and may contain discrete restudy / allocation risks that a simple continuous percentage distribution does not represent well.

Applying one percentage only to EPC therefore has no guaranteed relationship to the uncertainty of the whole project budget. The worked Project A / Project B comparison is designed to show that modelling point, not to establish a market contingency level.

Why Adding Every Individual High Case Can Overstate the Aggregate

Under the article's illustrative ranges:

EPC                        $190m × 6%      = $11.4m
Owner equipment             $12m × 20%     =  $2.4m
Interconnection             $20m × 50%     = $10.0m
Development                  $8m × 20%     =  $1.6m
                                              ------
Sum of individual highs                     = $25.4m

That sum treats every line as reaching its selected high case simultaneously.

Whether that is conservative or realistic depends on correlation and common risk drivers. Module escalation and EPC claims may move together. Schedule delay can increase IDC, owner costs and contractor claims at the same time. Interconnection delay can also move schedule and financing costs together.

So the correct alternative is not “assume diversification.” It is to model the dependencies explicitly.

The Worked Monte Carlo: Combine Distributions, Correlations and Events

For the simplified Project A illustration, assign distributions to the four budget lines and simulate total cost.

On the article's original independent triangular assumptions, the results are:

Confidence	Total cost	Contingency	As % of base
P50	$234.64m	$4.64m	2.0%
P80	$238.75m	$8.75m	3.8%
P90	$240.93m	$10.93m	4.8%
P95	$242.70m	$12.70m	5.5%

Under those assumptions, a $9.5m contingency is approximately P84.

Do not generalize that percentile. Three modelling choices can move it materially:

Correlation. Positive correlation widens the aggregate distribution relative to an independence assumption. AACE RP 118R-21 specifically calls out correlation as an important Monte Carlo consideration.

Discrete risk events. A tariff change, contractor insolvency, major restudy or permit challenge should not be smuggled into a smooth line-item range if it is a separate event with its own probability and impact. RP 118R-21 warns that estimate ranging used alone can understate contingency when significant project-specific events exist.

Bias / estimate quality. A base estimate that is already optimistic cannot be repaired merely by attaching a symmetric distribution around it.

The useful output is therefore not “Monte Carlo says P80 = $8.75m.” It is:

Base estimate quality
+ inherent uncertainty model
+ correlated / systemic effects
+ discrete event-risk model
= total cost distribution

Then compare the carried contingency with that distribution.

Now Change the Mix

Project B keeps the same $230m total base budget but shifts more cost into the higher-uncertainty interconnection line: $150m EPC and $60m interconnection.

Using the same illustrative distributions and the same simplifying independence assumption:

Confidence	Contingency	As % of base
P50	$6.08m	2.6%
P80	$16.05m	7.0%
P90	$21.09m	9.2%
P95	$24.74m	10.8%

An illustrative five-percent-of-EPC rule would carry $7.5m, approximately P55 under this model.

That does not prove that five percent of EPC is “wrong.” It proves that one percentage applied to one budget line can imply radically different confidence when the composition and risk drivers of total project cost change.

Re-run the same case with realistic positive correlations or discrete interconnection-event risks and the percentile will move again. That is why the confidence level is an output of the risk model, not a property of the contingency percentage.

Contingency, Management Reserve and Sponsor Support Are Different Buckets

Organizations use these labels differently, which is precisely why AACE RP 40R-08 says the meaning of “risk” and “contingency” should be agreed for the application.

For project-finance modelling, keep three concepts separate even if the transaction uses different names:

Budget contingency. Amount included in project uses and available under the construction budget subject to the draw controls in the financing documents.

Sponsor / management reserve. Capital held outside the project budget or lender-controlled sources and made available only if the sponsor chooses or is required to contribute it.

Committed cost-overrun support. Legally enforceable equity, subordinated debt, guarantee or other support that the lenders can call when available construction funds are insufficient.

The economic distinction is more important than the label. A dollar of financed contingency may be partly debt-funded; a dollar of external sponsor reserve may be 100% sponsor capital; committed support can exist without cash being funded on day one.

The Monte Carlo model must also state what it covers. A line-item estimate-ranging model can quantify inherent uncertainty. Discrete risk events need separate treatment where material. A sponsor reserve may be intended to protect against risks that were deliberately not included in the financed contingency.

Who Controls It, and When Is It Spent?

The construction credit agreement and approved budget determine control.

Filed project facilities show lenders and independent engineers monitoring budget sufficiency, remaining project costs and contingency. Some agreements restrict budget reallocations or require consent above specified thresholds; others allow transfers among categories within defined limits.

The monitoring metric worth building is:

Contingency used / contingency carried
vs
Physical completion / cost completion

A project consuming contingency faster than construction progresses can be an early warning that the cost-to-complete cushion is eroding.

Do not assume unspent contingency can simply be drawn at completion. Availability conditions, eligible-cost definitions, commitment reductions and final cost-to-complete certification determine whether unused capacity disappears, is reallocated, or remains available.

What About Schedule Contingency?

The other kind, and it is not interchangeable with the money kind.

Schedule contingency is float — time built into the programme beyond the critical path requirement. It protects the dates, and contracts and legal material established how many dates a project actually has: guaranteed substantial completion under the EPC contract, the PPA's guaranteed commercial operation date, the longstop date, and the tax credit placed-in-service deadline.

Two things make schedule contingency harder to size than cost contingency.

Float is consumed by events that do not cost money. A permit appeal, a grid outage postponing energisation, a weather window missed. None of those draws on the cost contingency and all of them consume the buffer protecting four different deadlines with four different consequences.

Converting time to money is not linear. The delay LD analysis showed that the cost of delay steps at each date rather than accruing smoothly — liquidated damages begin, then a cap exhausts, then a termination right arises, and the placed-in-service deadline is a cliff with no damages attached at all because there is no counterparty. A model that values float at a daily rate has assumed away the structure that makes delay dangerous.

The practical instruction is to size cost and schedule contingency separately, and to convert the schedule buffer into money using the date ladder rather than a flat daily figure. A project with sixty days of float against a longstop date and thirty days against a placed-in-service deadline is exposed on the second, whatever the first says — and it is the second that has no remedy.

What This Means in Practice

Three practical conclusions survive the corrections above.

Interconnection risk should be modelled on its own facts. A project with an immature network-upgrade estimate or material restudy / allocation exposure should not rely on a contingency percentage calibrated only to EPC cost.

Wrapping changes the risk allocation, not automatically the contingency answer. A fixed-price wrapped EPC can reduce some interface and price uncertainty, but change orders, exclusions, contractor credit and owner-retained scope still matter. Re-run the risk model after the contract structure is fixed rather than simply lowering contingency by convention.

Report confidence and uncovered event risks together. “P80 contingency” can sound comprehensive even when the simulation excludes contractor insolvency, tariff action or major schedule events. The credit committee should see both the percentile and the material risks outside the model.

How Do You Build This in Excel?

As a line-by-line distribution with a simulated total, and with the confidence level of whatever contingency you actually carry reported as an output.

The decomposition

For each budget line or risk driver:
   Base_Estimate
   Maturity / estimate basis
   Inherent uncertainty inputs
   Distribution choice
   Correlation group(s)
   Relevant discrete-event risks

The simulation

For each of N trials:
   1. Draw correlated inherent-uncertainty outcomes
   2. Draw material discrete risk events separately
   3. Apply event impacts to the affected cost / schedule lines
   4. Sum total project cost

Sort outcomes, then:
   PF_ContingencyP50 = PERCENTILE(Total, 50%) − Base
   PF_ContingencyP80 = PERCENTILE(Total, 80%) − Base
   PF_ContingencyP90 = PERCENTILE(Total, 90%) − Base

Excel can run the simulation with RAND()-driven inputs, data tables or workbook scripting. The required number of trials depends on the model and the stability of the percentile being reported; use a convergence check rather than a fixed “10,000 trials is always enough” rule.

The output that changes decisions

PF_ContingencyCarried        = the amount in the budget
PF_ImpliedConfidenceLevel    = percentile of (Base + Carried)

Project A:  $9,500,000  →  P84
Project B:  $7,500,000  →  P55

Publishing the implied confidence level is useful only together with the scope of the risk model. A P80 from a model that excludes a major discrete risk is not comparable with a P80 from one that includes it.

The cross-check against the cost-to-complete test

Contingency carried                              $7,500,000
Cost increase that fails cost-to-complete        = contingency remaining
→ At what percentage complete does the buffer run out?

The construction post identified the cost-to-complete test as the real completion covenant. Contingency is what stands between a cost increase and a failed test, so the two analyses belong together.

ℹ️ Note: Do not lift line-item ranges from an AACE process-industry class table into a renewable project. Use project-specific estimate maturity, historical data, contract scope, risk-register events and expert input. AACE itself says the selected risk method must be fit for use.

To build the decomposed contingency, the simulation and the implied confidence level, prompt Dezzmond with your budget lines and estimate classes.

What Do Sponsors and Lenders Actually Check?

• What confidence level does the carried contingency represent?
• Is contingency decomposed by line, or applied as a single percentage?
• What share of the budget sits outside the firm-priced EPC contract? That is where the uncertainty is.
• Is the interconnection estimate an executed agreement or a cluster study?
• Do the distributions and correlations reflect the actual risk drivers? Do not force asymmetry or independence merely because a generic example used them.
• Has the portfolio effect been applied, or is the total a sum of individual maxima?
• At what percentage complete does the contingency run out under an adverse case?

Frequently Asked Questions

What is contingency for?

A quantified allowance for the uncertainty and risks included within the estimate's defined scope. The exact definition should be agreed for the project, because organizations distinguish inherent uncertainty, event risks, contingency and management reserve differently.

Does AACE prescribe one accuracy range for each class?

No. AACE 18R-97 gives ranges of possible accuracy ranges for the process industries and says actual accuracy depends on project-specific systemic and event risks. It also expressly excludes power-generating facilities from that industry-specific practice. Use estimate class as a maturity indicator, not a renewable-project contingency lookup table.

Why not just add each line's high case?

That assumes the selected high outcomes occur together. A Monte Carlo model can represent how risks combine, but the result depends critically on correlation and event-risk assumptions. Independence can understate aggregate tail risk when multiple costs share the same driver.

Why can a percentage of EPC misstate protection?

Because EPC value is only one component of total project cost. If material uncertainty sits in owner-supplied equipment, interconnection, schedule, taxes or other owner-retained scope, an EPC-based percentage can imply a very different confidence level from project to project.

Is contingency the same as management reserve?

Not necessarily. Terminology and governance differ among organizations. For a financing model, distinguish the amount included in financed project uses, any sponsor-controlled reserve outside the budget, and any legally committed cost-overrun support.

Does cost contingency replace schedule-risk analysis?

No. Cost and schedule risks can interact, but schedule float, contractual milestone dates and statutory deadlines require their own analysis. An integrated cost-and-schedule risk model can capture those interactions where they are material.

What should be reported instead of only a percentage?

At minimum: the carried contingency, implied confidence level, risk-model scope, major exclusions, correlation assumptions and material discrete risks. “P80” without that context can be misleading.

Closing: The Number That Absorbs Every Other Error

Thirteen posts on project finance mechanics, and they end on the line that catches whatever the other twelve got wrong.

Contingency is the last defence in the capital budget. The sources and uses statement balances by adjusting equity; the cost-to-complete test forces the sponsor to fund a shortfall; and between those two sits contingency, which is supposed to absorb the ordinary variation so that neither mechanism has to be invoked.

Sizing it by convention means sizing the last defence without knowing how strong it is. And the convention has a specific and perverse failure: it scales with the firm-priced portion of the budget, so a project whose cost risk is concentrated in an unfixed interconnection estimate — which describes a great many projects in congested zones right now — receives the least protection precisely because it has the most exposure.

The fix is not more contingency. On Project A the convention was already generous at P84. The fix is to know which case you are in, which requires decomposing the budget by estimate class, combining the distributions rather than adding the maxima, and reporting a confidence level instead of a percentage.

That is a morning's work in a spreadsheet, and it converts the most-argued-about line in a capital budget into one of the few numbers in this series that can be compared directly across projects.

The returns and valuation collection begins next, on returns and valuation: what the different IRRs actually measure, and why the one most often quoted is the one that says least.

Sources: AACE RP 40R-08 — Contingency Estimating: General Principles · AACE RP 118R-21 — Cost Risk Analysis and Contingency Determination Using Estimate Ranging with Monte Carlo Simulation · AACE RP 18R-97 — Cost Estimate Classification for the Process Industries · Dezzmond analysis; Project A / B distributions and percentiles are illustrative.