AACE CCP common mistakes
AACE CCP · Understand the traps and how to avoid them.
Assigning an estimate class by how much work has been done on the deliverable, rather than by the dual criteria: the maturity level of project definition (percent of engineering/definition complete) and the expected accuracy range. Candidates label a screening estimate 'Class 3' because 'it feels mid-stage', then pick accuracy ranges that do not match the class.
The class table is memorized as a single ordered list ('Class 5 is worst, Class 1 is best') rather than as a two-dimensional matrix, so the definition-maturity column is dropped under time pressure.
What to do instead
Build a one-page matrix with two columns (definition maturity %, accuracy range low/high) for Classes 5 through 1 and reproduce it from memory weekly until it is exact. On every practice item, write down both the maturity percentage given in the stem and the range before looking at the options.
Treating escalation as a flat percentage added once to a base-year cost, or applying a cost index to the wrong base (e.g., dividing when the index should be multiplied). Similarly, compounding escalation by adding the annual rate times the number of years instead of compounding it.
Escalation is confused with contingency, and index arithmetic is done by feel ('the index went up, so the cost goes up') without anchoring to the base year stated in the stem.
What to do instead
Always write the ratio explicitly with labels before computing: Cost(n) = Cost(base) x Index(n) / Index(base). For multi-year escalation, write the compounding exponent for each year on the timeline. Do ten index and ten escalation drills until the direction of the ratio is automatic.
Applying a learning-curve percentage to each individual unit's hours instead of to the cumulative average hours, and forgetting that unit cost requires hours multiplied by the fully burdened labour rate (base wage plus fringes plus overhead), not the base wage alone.
The '80% curve' is remembered as 'each unit takes 80% of the previous unit', which is the unit-curve convention, not the cumulative-average convention that most exam items intend; burden is skipped because the stem quotes an hourly wage prominently.
What to do instead
Before solving, write one line stating which convention applies and the doubling rule you will use. Set up a small table with columns: unit number, cumulative average hours, total hours, incremental hours. Convert to dollars only in the last step, using the burdened rate.
Reporting total float when the question asks for free float (or vice versa), and freezing when a constraint or an out-of-sequence relationship produces negative float instead of treating negative float as a signal that the constrained finish date is unachievable without acceleration.
Both terms are learned as 'slack', so candidates substitute one for the other; negative float is treated as an error in the calculation rather than as a legitimate result of a imposed date.
What to do instead
Drill the definitions until they are reflexive: total float = late finish minus early finish (shared along the path); free float = early finish minus early start of the earliest successor. For negative float, always trace which constraint or external date is driving it and state that mitigation is required.
Ignoring lags and leads when summing path durations, dropping a path because it 'looks short' without summing every path, and mixing calendars (a 5-day and a 7-day calendar in the same network) without converting durations to a common basis.
Candidates scan the diagram for the visually longest chain rather than enumerating all paths, and lags are drawn as small annotations that are easy to overlook; multiple calendars are rarely encountered in day-to-day scheduling.
What to do instead
Enumerate every path start-to-finish on scratch paper, writing the sum including each lag with its sign. If more than one calendar appears, convert all durations to working days (or calendar days) first and note the conversion. Confirm the critical path by comparing the longest path total to the backward-pass result.
Using one forecast formula for every EAC question - most often EAC = BAC/CPI - even when the stem describes a one-time, non-recurring variance, or when the schedule is driving cost. Also using the composite EAC = ACWP + (BAC - BCWP)/(CPI x SPI) when the stem says the cost variance is atypical.
One formula gets memorized as 'the' EAC formula during last-minute review, and the diagnostic question implied by the stem (will the variance continue?) is never asked.
What to do instead
Before computing, classify the variance out loud: (a) atypical/one-time, (b) typical cost performance, (c) both cost and schedule performance driving. Then select: (a) AC + (BAC - EV); (b) AC + (BAC - EV)/CPI; (c) AC + (BAC - EV)/(CPI x SPI). Practise ten stems where the only difference is that classification sentence.
Accepting a percent-complete figure based on cost incurred, elapsed time, or units installed when the stem specifies a different measurement basis, and conflating BCWP with the percent complete reported by the performing organization. Level-of-effort and apportioned activities are also treated as if they earned value on physical progress.
Percent complete is treated as a single universal number rather than a method-dependent metric; earned value and reported progress are assumed to be the same thing because both are 'how much is done'.
What to do instead
Memorize the four measurement bases (units completed, incremental milestones, percent complete with fixed formula, level of effort/apportioned) and their appropriate use. On any progress item, underline the measurement basis named in the stem and reject options built on a different basis, even if the arithmetic is correct.
Using contingency, management reserve, and escalation as interchangeable terms - for example, charging an identified-but-unquantified scope risk to management reserve, or adding escalation into the contingency line so it is counted twice. Related: attributing approval authority for management reserve to the project manager.
In practice these are often blended in a single 'reserve' spreadsheet line, and the exam tests the formal distinction between known-unknowns owned by the project manager and unknown-unknowns owned by management above the project.
What to do instead
Write a three-row comparison card: contingency (known-unknowns, inside the cost baseline, PM authority), management reserve (unknown-unknowns, outside the baseline, sponsor/management authority), escalation (identified time-based price movement, treated explicitly in the base estimate or as a separate allowance). Recite it before any reserve question.
Choosing the alternative with the highest IRR over the one with the highest positive NPV when the two are mutually exclusive, or accepting an IRR result on a cash flow stream with more than one sign change without checking for multiple roots. Also rejecting a project whose IRR exceeds the hurdle rate but whose NPV is negative due to a discounting error.
IRR is expressed as an intuitive percentage while NPV is an absolute dollar figure, so 'bigger percentage' feels like 'better project'; scale and timing differences between alternatives are not considered.
What to do instead
Adopt a fixed decision hierarchy to apply mechanically: for mutually exclusive alternatives, rank by NPV at the given discount rate; use IRR only for screening against the hurdle rate and for independent projects. When cash flows change sign more than once, note that IRR is not a reliable ranking tool and state the MIRR or NPV basis instead.
Mixing constant-value (real) dollars with then-current (nominal) dollars in the same analysis, or discounting nominal cash flows at a real discount rate. Related: applying the escalation rate as the discount rate, and mishandling depreciation and taxes in after-tax cash flow by deducting the full capital cost and also deducting depreciation.
The words 'escalation' and 'discount rate' both describe money changing over time, so the two get collapsed into one rate; capital cost is double-counted because it 'feels' like both an outflow and a tax shield.
What to do instead
Write the rule at the top of your scratch paper before any economic item: nominal cash flows with nominal rates, or constant dollars with real rates - never mixed. For after-tax flows, build a small year-by-year table with rows for revenue, operating cost, depreciation (non-cash), taxable income, tax, and net cash flow; never deduct capital cost twice.