PSP — AACE Planning & Scheduling Professional Quick Reference

Last revised: July 1, 2026

Compact PSP exam reference for AACE International Planning & Scheduling Professional candidates: CPM, float, updates, controls, risk, resources, and delay analysis.

Exam Identity and Use

This Quick Reference supports independent review for the AACE International AACE Planning & Scheduling Professional (PSP) exam, code PSP. It is designed for fast recall of planning, scheduling, controls, and delay-analysis concepts commonly tested in professional scheduling contexts.

Use it to check:

CPM network calculation steps
Float, logic, constraint, and calendar distinctions
Schedule development and update workflow
Baseline, progress, and forecast terminology
Earned value and schedule-control formulas
Resource, risk, and delay-analysis decision points

Core Planning vs. Scheduling Distinctions

Concept	Planning emphasis	Scheduling emphasis	Exam trap
Purpose	Define scope, strategy, sequence, means and methods	Time-phase the plan into activities, logic, dates, resources	A schedule without a credible plan is just dated activity data
WBS	Deliverable-oriented decomposition	Basis for activity coding and reporting	WBS is not automatically the activity list
Activity	Work package or task to be performed	Network element with duration, logic, calendar, responsibility	Activities need measurable scope and update rules
Milestone	Key event or decision point	Zero-duration network marker	Milestones should have logic, not just imposed dates
Baseline	Approved plan for comparison	Frozen schedule/cost/time reference	Do not overwrite baseline with current forecast
Forecast	Current prediction of future outcome	Updated projected dates and completion	Forecast variance is measured against baseline or target
Control	Compare, analyze, act	Update, report, correct, reforecast	Reporting variance is not the same as controlling it

Planning and Scheduling Lifecycle

Step	Main output	Key checks
Define scope and execution strategy	WBS, scope basis, sequencing assumptions	Scope completeness, interfaces, constraints
Develop activity list	Activities, milestones, codes	Measurable work, appropriate level of detail
Sequence work	Network logic	Mandatory vs discretionary logic; no open ends unless justified
Estimate durations	Activity durations and basis	Quantity, production rate, crew, calendar, risk allowance
Assign calendars/resources	Calendars, resource plan, cost loading if required	Calendar consistency; resource feasibility
Calculate CPM	Early/late dates, float, critical path	Logic-driven path, not just longest activity chain
Review and baseline	Approved baseline schedule	Quality checks, stakeholder acceptance, change-control readiness
Update progress	Actuals, remaining durations, data date status	No actuals after data date; no planned work before data date
Analyze variance	Variance, trend, recovery options	Separate cause, effect, and corrective action
Forecast and control	Updated forecast, reports, mitigation	Forecast must reflect current logic and remaining work

Schedule Model Building Blocks

Element	What it represents	Good practice	Common PSP-style trap
Activity ID	Unique identifier	Stable coding convention	Renumbering can disrupt traceability
Activity description	Clear work statement	Verb + object + location/system	Vague descriptions weaken progress measurement
Duration	Planned work time	Based on quantity, productivity, calendar	Duration is not the same as work-hours
Logic predecessor/successor	Network dependency	Mostly finish-to-start where appropriate, with justified alternatives	Excessive lags can hide work scope
Calendar	Working/nonworking time	Match trade, shift, weather, contract rules	Calendar differences affect float and criticality
Constraint	Date restriction	Use only when externally justified	Hard constraints can override logic and create misleading float
Resource	Labor, equipment, material, crew	Use for feasibility and histograms	Resource leveling can change critical path
Activity code	Classification attribute	WBS, area, phase, discipline, contractor	Codes support filtering but do not replace logic
Baseline	Approved reference	Preserve for comparison	Updating baseline without approval destroys variance history

CPM Calculation Reference

Forward and Backward Pass

Use the date convention stated in the problem or schedule tool. Two common conventions appear in exam-style questions:

Convention	Forward pass	Backward pass	Float
Zero-based / elapsed time	EF = ES + duration	LS = LF - duration	TF = LS - ES = LF - EF
Inclusive day numbering	EF = ES + duration - 1	LS = LF - duration + 1	TF = LS - ES = LF - EF

If the question gives activities starting at day 0, use elapsed-time math. If it gives work starting on day 1 and counts both first and last day, use inclusive math.

Core CPM Terms

Term	Meaning	Formula or rule
ES	Earliest an activity can start	Maximum of predecessor-driven start dates
EF	Earliest an activity can finish	ES + duration, or ES + duration - 1 under inclusive convention
LF	Latest an activity can finish without delaying required completion	Minimum of successor-driven late dates
LS	Latest an activity can start without delaying required completion	LF - duration, or LF - duration + 1 under inclusive convention
Total float	Time activity can slip without delaying project completion or required finish	LS - ES, or LF - EF
Free float	Time activity can slip without delaying an immediate successor’s early start	Minimum successor ES - activity EF, adjusted for convention and relationship
Critical path	Longest path or path with least total float	Can have zero, positive, or negative float depending on required finish
Negative float	Required date is earlier than logic-driven completion	Indicates compression need, constraint issue, or missed requirement
Near-critical path	Path close to critical	Watch for risk; may become critical after updates
Longest path	Driving path to completion based on continuous logic	Often more reliable than simply filtering zero float when constraints exist

Logic Relationship Reference

Relationship	Meaning	Successor timing condition, elapsed convention
FS	Finish-to-start: successor starts after predecessor finishes	Succ ES >= Pred EF + lag
SS	Start-to-start: successor starts after predecessor starts	Succ ES >= Pred ES + lag
FF	Finish-to-finish: successor finishes after predecessor finishes	Succ EF >= Pred EF + lag
SF	Start-to-finish: successor finishes after predecessor starts	Succ EF >= Pred ES + lag

Lead and Lag

Item	Meaning	Use carefully
Lag	Waiting time between related activities	May represent curing, delivery, review period, or hidden work
Lead	Negative lag allowing overlap	Often increases risk; should not replace proper activity breakdown
Excessive lag	Large unexplained delay	Can mask missing activities or poor planning
Prefer activity over lag when	The time interval consumes resources, has risk, or needs tracking	Example: “submittal review” is usually better as an activity than a long lag

Float Types and Interpretation

Float type	Definition	Exam-relevant interpretation
Total float	Delay allowed before project/required completion is delayed	Shared by activities on the same path
Free float	Delay allowed before delaying immediate successor early date	Belongs to the activity relative to its successors
Interfering float	Portion of total float beyond free float	Delay may affect successor early dates but not final completion
Independent float	Delay possible without affecting predecessors or successors	Usually limited; less common in practical software reporting
Negative float	Amount by which schedule misses imposed/required date	Not “extra critical”; it signals required recovery or date conflict
Float ownership	Contractual/governance issue	Do not assume contractor or owner owns float unless the governing documents say so

Critical Path and Constraint Traps

Situation	What can go wrong	Better exam answer
Hard finish constraint	Activity appears critical because of imposed date	Check logic-driven longest path and constraint impact
Must-start constraint	Forces activity to start despite predecessor logic	Challenge if not externally required
Open-ended activity	Missing predecessor or successor gives false float	Add appropriate logic unless it is a legitimate start/finish milestone
Out-of-sequence progress	Actual progress violates planned logic	Decide whether to retain logic, override logic, or revise logic based on update rules
Calendar mismatch	Same logic produces unexpected float	Check calendars before concluding calculation error
Multiple calendars on one path	Criticality can shift unexpectedly	Confirm driving relationships and working-day assumptions
Resource leveling	Dates change due to resource limits	Resource-critical path may differ from pure CPM path
Excessive constraints	CPM becomes date-pushed instead of logic-driven	Use constraints sparingly and document the reason

Schedule Quality Review Checklist

Check	What to look for	Why it matters
Complete logic	Activities generally have predecessors and successors	Open ends distort CPM
Valid activity scope	Activities have clear deliverables or measurable work	Enables reliable updates
Reasonable durations	Not too long for meaningful control	Long activities hide variance
Proper milestones	Zero duration, logically tied	Date markers should be driven or justified
Limited hard constraints	Externally justified only	Constraints can mask true critical path
Limited leads/lags	Documented and reasonable	Hidden work or risk may be missed
Calendar review	Correct work periods, holidays, shifts	Dates and float depend on calendars
Cost/resource loading	Matches estimate and execution plan	Supports S-curves, histograms, EV analysis
Baseline integrity	Approved and preserved	Enables variance analysis
Update validity	Actual dates, remaining durations, data date logic are coherent	Prevents invalid forecasts

Duration Estimating and Productivity

Common Duration Logic

Duration is often derived from quantity, production rate, and crew/calendar assumptions:

\[ \text{Duration} = \frac{\text{Quantity}}{\text{Production Rate per Time Period}} \]

If production rate is crew-dependent:

\[ \text{Duration} = \frac{\text{Quantity}}{\text{Crew Size} \times \text{Productivity per Crew Member per Period}} \]

Three-Point Estimating

\[ \text{PERT Expected Duration} = \frac{O + 4M + P}{6} \]\[ \text{PERT Standard Deviation} = \frac{P - O}{6} \]\[ \text{PERT Variance} = \left(\frac{P - O}{6}\right)^2 \]

Symbol	Meaning
O	Optimistic estimate
M	Most likely estimate
P	Pessimistic estimate

Estimate type	Formula	Use
Deterministic	Single duration	When uncertainty is low or detail is sufficient
Triangular mean	(O + M + P) / 3	Simple three-point average
PERT beta mean	(O + 4M + P) / 6	Weights most likely estimate more heavily
Parametric	Quantity / production rate	Good when measurable quantities and historical rates exist
Analogous	Based on similar past work	Useful early, less precise

Schedule Updating Reference

Update item	Correct treatment
Data date	Boundary between actual performance and forecast work
Actual start	Enter when work has actually begun
Actual finish	Enter when activity is complete
Remaining duration	Best forecast of time required after data date
Percent complete	Must match the method used: duration, physical, units, or cost
Expected finish	Forecast finish based on remaining work and logic
Suspended work	Reflect with actuals, remaining duration, and sometimes split activity if allowed
Deleted work	Remove or zero out only under approved change/update procedure
Added work	Add activities with proper logic, codes, baseline/change treatment
Out-of-sequence progress	Apply project update policy; analyze impact on logic and forecast

Percent Complete Types

Type	Based on	Useful when	Trap
Duration percent complete	Time elapsed versus planned/current duration	Work progresses roughly with time	Can overstate progress when little physical work is done
Physical percent complete	Measured installed/complete work	Quantity-based field work	Requires objective measurement rules
Units percent complete	Installed quantity / total quantity	Repetitive measurable work	Quantity installed may not equal earned value if weighting differs
Cost percent complete	Cost incurred / budget	Cost-tracked work	Spending money is not the same as earning progress

Baseline, Current, Forecast, and As-Built

Schedule version	Meaning	Used for
Baseline schedule	Approved original or approved revised plan	Variance and performance comparison
Current schedule	Latest updated schedule model	Status reporting and forecast
Forecast schedule	Projection from data date forward	Completion prediction and mitigation
Recovery schedule	Plan to regain required dates	Acceleration, resequencing, added resources
What-if schedule	Scenario analysis copy	Decision support, not the official record
As-built schedule	Actual sequence and dates of completed work	Delay analysis and lessons learned
Fragnet	Fragmentary network representing a change or delay event	Time impact analysis and change evaluation

Variance and Earned Value Formula Sheet

Metric	Plain formula	Meaning
PV	Planned Value	Budgeted value of work planned by status date
EV	Earned Value	Budgeted value of work actually performed
AC	Actual Cost	Actual cost incurred for performed work
BAC	Budget at Completion	Total approved budget
CV	EV - AC	Cost variance
SV	EV - PV	Schedule variance in value terms
CPI	EV / AC	Cost efficiency
SPI	EV / PV	Schedule efficiency by earned value
EAC	AC + ETC	Forecast final cost
EAC, CPI method	BAC / CPI	Assumes future cost efficiency follows current CPI
ETC	EAC - AC	Forecast cost to complete remaining work
VAC	BAC - EAC	Variance at completion
TCPI to BAC	(BAC - EV) / (BAC - AC)	Required future efficiency to meet BAC
TCPI to EAC	(BAC - EV) / (EAC - AC)	Required future efficiency to meet EAC

Earned Value Interpretation

Condition	Meaning
CV > 0	Under budget for work performed
CV < 0	Over budget for work performed
SV > 0	More value earned than planned by status date
SV < 0	Less value earned than planned by status date
CPI > 1.0	Cost efficiency favorable
CPI < 1.0	Cost efficiency unfavorable
SPI > 1.0	EV progress ahead of planned value
SPI < 1.0	EV progress behind planned value

PSP trap: EV schedule variance does not identify the CPM critical path. A project can have favorable SPI while a critical milestone is forecast late.

Schedule Variance and Date Metrics

Metric	Formula or method	Notes
Finish variance	Forecast finish - baseline finish	Positive/negative convention may vary; read the question
Start variance	Actual or forecast start - baseline start	Useful for early detection
Total float variance	Current float - baseline float	Float erosion can signal risk
Critical path drift	Compare baseline critical path to current driving path	Path may shift after updates
Milestone slip	Forecast milestone date - baseline milestone date	Report key contractual or management dates
Progress planned vs actual	Actual quantity or EV compared with planned	Needs consistent measurement basis

Resource Planning and Leveling

Term	Meaning	Exam distinction
Resource loading	Assigning labor/equipment/material quantities to activities	Supports histograms, cost loading, feasibility
Resource histogram	Time-phased resource demand chart	Shows peaks, shortages, staffing needs
Resource leveling	Adjusting dates to resolve resource overallocations	May delay completion and change critical path
Resource smoothing	Adjusting within available float	Does not delay required completion if float is sufficient
Crew logic	Sequencing based on crew movement or production flow	Important for repetitive work
Cost loading	Assigning budget/cost to activities	Supports cash flow and earned value
S-curve	Cumulative planned/earned/actual value or quantity	Used for trend and progress comparison

Leveling vs. Smoothing

Question clue	Better answer
Resource limit cannot be exceeded and completion may move	Resource leveling
Completion date must remain unchanged and only float may be used	Resource smoothing
Need to show labor demand by week/month	Resource histogram
Need cumulative planned vs actual cost/progress	S-curve
Need optimize repetitive crew production	Line-of-balance or location-based planning concept

Schedule Compression

Method	What it does	Advantages	Risks
Crashing	Adds resources, overtime, shifts, or methods to shorten duration	Can preserve sequence	Higher cost, congestion, productivity loss
Fast tracking	Overlaps activities previously planned in sequence	May save time without added direct resources	Rework, coordination risk, quality issues
Resequencing	Changes logic or work packaging	May remove inefficiencies	Must remain technically feasible
Scope reduction	Removes or defers work	Direct schedule relief	Requires approval and may affect objectives
Calendar change	Adds workdays/shifts	Simple to model	Labor, fatigue, access, cost, and productivity impacts

Compression Decision Table

If the issue is…	Consider first	Avoid assuming
Negative float from imposed finish	Validate constraint and longest path	That all critical activities need crashing
One delayed procurement item	Alternative supplier, resequencing, mitigation fragnet	That field labor acceleration solves it
Critical activity has high labor content	Crashing or shift work	Linear productivity improvement
Critical path has finish-to-start logic with feasible overlap	Fast tracking	No rework risk
Noncritical activity is late but has float	Monitor or use float	That every late activity delays the project
Resource overload drives delay	Leveling alternatives, smoothing, added crews	That CPM float alone solves resource limits

Risk and Uncertainty in Schedules

Concept	Meaning	PSP-relevant use
Schedule risk	Uncertainty affecting activity durations, logic, resources, calendars, or external events	Drives contingency and confidence analysis
Risk register	List of risks, causes, effects, responses, owners	Links risk to schedule activities where possible
Contingency	Time or cost allowance for identified risk	Should be transparent and governed
Management reserve	Allowance for unknowns or management-controlled risk	Not the same as activity padding
Monte Carlo simulation	Repeated sampling of uncertain durations/risks	Produces date confidence ranges
Criticality index	Frequency activity appears on critical path in simulation	Shows probabilistic importance
Sensitivity analysis	Shows variables most affecting outcome	Helps target mitigation

Risk Formulas

\[ \text{Expected Monetary Value} = \text{Probability} \times \text{Impact} \]\[ \text{Expected Duration Impact} = \text{Probability} \times \text{Duration Impact} \]

Risk response	Use when
Avoid	Change plan to eliminate threat
Mitigate	Reduce probability or impact
Transfer	Shift responsibility by contract, insurance, or supplier arrangement
Accept	Monitor and use contingency if risk occurs
Exploit	Ensure an opportunity occurs
Enhance	Increase probability or benefit of an opportunity
Share	Allocate opportunity ownership to party best able to capture it

Change Control and Fragnets

Item	Role in scheduling
Change event	New scope, delay, disruption, acceleration, or changed condition
Fragnet	Network fragment showing added/changed work and logic ties
Time impact analysis	Prospective insertion of fragnet into an accepted schedule update
Approved change	May justify baseline revision or separate change log
Pending change	Often tracked in current forecast but not baseline until approved
Change log	Records description, status, cost/time impact, responsibility

Change-Control Decision Table

Scenario	Scheduler’s best next step
New work is authorized	Add activities/fragnet, logic, resources, and baseline/change coding
Potential change is not yet approved	Model what-if or pending impact per procedure; do not silently alter baseline
Change affects critical path	Analyze time impact against data date and current accepted schedule
Change affects only noncritical work	Check float consumption and milestone effects
Owner requests recovery plan	Preserve current update, create recovery scenario, document assumptions
Baseline revision requested	Confirm approval path and retain prior baseline for audit trail

Delay Analysis Quick Reference

Method	Basic idea	Best suited for	Limitations
As-planned vs. as-built	Compare planned dates/sequence to actual dates/sequence	Simple overview	May ignore changing critical path and updates
Impacted as-planned	Insert delay events into baseline/as-planned schedule	Prospective or simple event modeling	Can ignore actual progress and later changes
Time impact analysis	Insert fragnet into current accepted update at time of event	Prospective change/time extension analysis	Depends on quality of update and fragnet logic
Windows analysis	Evaluate delay in discrete time windows using updates	Projects with periodic updates	Requires reliable updates and careful window selection
Collapsed as-built	Remove delay events from as-built to estimate but-for completion	Retrospective analysis	Sensitive to logic reconstruction assumptions
Contemporaneous period analysis	Uses schedule updates and records from the time	Retrospective with project records	Data quality is critical

Delay Classification

Classification	Meaning	Possible schedule result
Excusable delay	Delay not caused by contractor, often beyond contractor control	May support time extension
Non-excusable delay	Delay caused by contractor responsibility	Usually no time extension
Compensable delay	Delay for which additional compensation may be allowed under governing documents	Time and cost may be considered
Non-compensable delay	Time may be allowed without additional compensation	Depends on governing documents
Concurrent delay	Separate delays by different parties affect critical path during same period	Requires careful critical-path and responsibility analysis
Pacing delay	One party slows work because another delay already controls completion	Requires evidence of intent and criticality

Do not assume legal entitlement from a schedule calculation alone. PSP questions usually require separating technical schedule impact from contractual entitlement.

Concurrency and Criticality Traps

Trap	Correct reasoning
Two delays occur in the same month, so they are concurrent	They must both affect critical completion during the same analysis period
A delay to a noncritical activity always has no effect	It may consume float and become critical later
A critical activity delay always delays project completion	Only if it affects the controlling path and is not offset by mitigation or float changes
Baseline critical path stays critical forever	Updates can shift the driving path
Delay days equal calendar days automatically	Check applicable activity calendars and nonwork periods
Float consumption equals compensable delay	Float use and entitlement are separate issues

Reporting and Communication

Report type	Shows	Use
CPM schedule report	Activity dates, logic, float, critical path	Technical schedule review
Milestone report	Key dates and variance	Executive and contractual reporting
Lookahead schedule	Near-term planned work, often 2-6 weeks	Field coordination
Variance report	Baseline vs current/forecast differences	Control and corrective action
Narrative report	Explanation of progress, critical path, delays, risks	Converts data into management meaning
S-curve	Cumulative planned, earned, actual	Trend and production/cost visibility
Resource histogram	Labor/equipment demand by period	Staffing and resource planning
Exception report	Late, critical, near-critical, constrained, missing logic	Focused schedule health review

Good Schedule Narrative Elements

Data date and reporting period
Work completed during the period
Current critical path and near-critical paths
Major variances from baseline or previous update
Delays, causes, and responsible mitigation actions
Changes added, pending, or approved
Forecast milestone and completion dates
Risks and recovery actions
Assumptions affecting the forecast

Artifact Selection Matrix

Need	Use this artifact
Decompose project scope	WBS
Show sequence and dependencies	CPM network
Show key contractual dates	Milestone schedule
Show near-term field commitments	Lookahead schedule
Show crew flow by location	Line-of-balance or location-based schedule
Show labor demand	Resource histogram
Show cumulative progress or cost	S-curve
Evaluate change impact	Fragnet and time impact analysis
Preserve approved comparison point	Baseline schedule
Analyze completed delay	As-built schedule and retrospective delay method
Track schedule risk	Risk register and schedule risk model

“What Should the Scheduler Do Next?” Decision Table

Situation in question	Best next action
Schedule has missing successors and predecessors	Correct logic before relying on float or critical path
Activity shows negative float	Identify imposed requirement/constraint and analyze recovery options
Actual work appears after the data date	Correct the update; actuals must not be in the future
Planned work remains before the data date	Update status and remaining duration or revise forecast
Critical path changed since last update	Explain why: progress, logic, calendar, resource, or constraint change
Stakeholder asks to shorten project	Analyze critical/near-critical paths before recommending crashing
Delay event occurs during active project	Use contemporaneous update and fragnet for time impact if appropriate
Progress percent seems high but quantities are low	Verify percent complete method
Resource histogram exceeds available labor	Level, smooth, resequence, or add resources; assess date impact
Baseline dates no longer match approved scope	Use formal change/baseline revision process
Report shows favorable SPI but completion is late	Check CPM critical path; EV SPI may not reflect milestone risk

High-Yield Formula Summary

\[ \text{Total Float} = LS - ES = LF - EF \]\[ \text{Free Float} = \text{Earliest Successor Start} - \text{Activity Early Finish} \]\[ \text{Duration} = \frac{\text{Quantity}}{\text{Production Rate}} \]\[ \text{CPI} = \frac{EV}{AC} \]\[ \text{SPI} = \frac{EV}{PV} \]\[ \text{CV} = EV - AC \]\[ \text{SV} = EV - PV \]\[ \text{EAC} = AC + ETC \]\[ \text{VAC} = BAC - EAC \]\[ \text{PERT Expected Duration} = \frac{O + 4M + P}{6} \]

Final Review Checklist

Before exam day, make sure you can:

Perform a forward and backward pass under the date convention given.
Identify total float, free float, negative float, and the controlling path.
Explain how constraints, calendars, lags, and resources can distort criticality.
Distinguish baseline, current, forecast, recovery, and as-built schedules.
Choose the correct artifact for planning, updating, reporting, change, or delay analysis.
Interpret EV metrics without confusing EV schedule variance with CPM delay.
Select an appropriate delay-analysis method from the facts given.
Recognize when the best answer is to validate the schedule model before calculating impact.
Separate technical schedule analysis from contractual entitlement assumptions.

For the next step, work timed PSP-style practice questions that require CPM calculations, update interpretation, variance analysis, and delay-method selection rather than only memorizing terms.

Scenario Guide

Conduct Planning Duties