Estimate and Build the Schedule

Introduction

This lesson covers the first half of task 8 of the Process domain in the July 2026 PMP Examination Content Outline (Process carries 41% of the exam): determine the schedule approach that fits the development approach, coordinate with other projects and operations, estimate tasks, use benchmarks and historical data, build the network and find the critical path, and plan releases and iterations. The second lesson covers baselining, executing, compressing, and analyzing schedule variation.

Schedule questions combine calculations (forward and backward pass, float, three-point estimates) with judgement (which technique suits an agile team, how to handle a dependency on another project). After this lesson you will be able to choose a scheduling approach, estimate with several techniques, draw a network diagram, compute the critical path and float, and plan releases and iterations in an adaptive project.

Learning objectives

• Select a schedule approach that matches the development approach (predictive, agile, hybrid).
• Estimate durations with analogous, parametric, bottom-up, three-point, and relative techniques.
• Use benchmarks, historical data, and expert input to improve estimates.
• Identify task dependencies (finish-to-start and others, leads and lags) and the types of dependency.
• Compute early and late dates, total float, free float, and the critical path.
• Coordinate the schedule with other projects, operations, and resource calendars.
• Plan releases, iterations, and the roadmap for adaptive work.

1. Choose the schedule approach

The schedule approach follows the development approach selected during planning.

Rolling wave planning is common: work in the near term is planned in detail, and later work stays at a higher level until more is known. It is progressive elaboration applied to the schedule.

Example: two schedules in one project

A company builds a smart thermostat. The hardware team has a supplier lead time of 14 weeks for chips and a safety certification slot booked for week 30, so it uses a predictive network with fixed milestones. The firmware and app teams work in two-week sprints with a roadmap. The project manager keeps one integrated milestone schedule: chips arrive week 14, the firmware feature-complete release is week 24, certification starts week 30. Inside those milestones the software teams plan by sprint. A single method for everything would either over-plan the software or under-plan the hardware.

2. Define activities and sequence them

In a predictive project, work packages from the WBS are decomposed into activities that can be estimated, assigned, and tracked. In agile work, epics are split into user stories and then into tasks within the iteration.

Dependency relationships

Lead advances the successor (an overlap): start painting 2 days before the plaster finishes. Lag delays the successor: wait 3 days for the concrete to cure.

Dependency types by cause

• Mandatory (hard logic): required by physics or contract. You cannot test software before it exists.
• Discretionary (soft logic): preferred practice or best practice; can be changed to compress the schedule.
• External: relies on something outside the project, such as a regulator's approval or a supplier delivery.
• Internal: relies on another project activity or team.

Understanding the cause matters for compression: discretionary dependencies are the first candidates for fast tracking; external ones need negotiation.

3. Estimating

An estimate is a quantitative assessment of the likely amount or outcome. Estimates should state the basis of estimate (assumptions, constraints, range, confidence level).

Estimating techniques

Three-point estimates

• Triangular: E = (O + M + P) / 3
• Beta (PERT): E = (O + 4M + P) / 6, standard deviation = (P - O) / 6, variance = ((P - O) / 6) squared.

Worked example: PERT estimate

Scenario. An activity "configure the data pipeline" has optimistic 8 days, most likely 12 days, pessimistic 22 days. What is the expected duration and the range with about 68% confidence?

Step 1: PERT expected value. E = (8 + 4 x 12 + 22) / 6 = (8 + 48 + 22) / 6 = 78 / 6 = 13 days.

Step 2: standard deviation. (22 - 8) / 6 = 14 / 6 = 2.33 days.

Step 3: 68% range. 13 plus or minus 2.33 gives about 10.7 to 15.3 days. About 95% (two standard deviations) is 8.3 to 17.7 days.

Step 4: compare with the triangular estimate. (8 + 12 + 22) / 3 = 14 days. PERT weights the most likely value more heavily, so it is lower here.

Why other choices are weaker. Using only the most likely value (12) ignores risk of delay. Using the pessimistic value (22) for every activity builds a large padding that wastes time and funds. Padding each task secretly hides the risk and invites Parkinson's law (work expands to fill the time available).

Estimating in agile teams

Agile teams estimate in story points (relative size) using techniques such as planning poker or affinity grouping. The velocity (points completed per iteration) turns relative estimates into a forecast: if the backlog holds 240 points and the stable velocity is 30 points per iteration, the forecast is 240 / 30 = 8 iterations. Use a range (for example velocity between 26 and 34 gives 7.1 to 9.2 iterations) rather than a single number. Large items are split before they are estimated; items that are too big or too unclear are subjected to a time-boxed spike to reduce uncertainty.

Benchmarks and historical data

Organizational process assets such as past project schedules, productivity rates, lessons learned, and industry benchmarks improve estimates. Compare your estimate against benchmarks: if a similar mobile app took 24 to 30 weeks in four previous projects and your plan shows 12 weeks, either the scope differs or the estimate is optimistic. Document the reasoning. Beware of using data from teams with different skills or technology as if they were identical.

Cognitive traps

• Anchoring: the first number mentioned dominates.
• Optimism bias and planning fallacy: people underestimate time for their own work.
• Student syndrome: starting only at the last moment.
• Padding: each level adds a hidden buffer.

Counter them with ranges, reference-class data, independent review, and explicit schedule reserves.

4. Build the schedule: network diagram and critical path

The critical path method (CPM) finds the longest path through the network, which is the shortest possible project duration, and calculates float.

Definitions

• Early start (ES) and early finish (EF): earliest dates, found in the forward pass.
• Late start (LS) and late finish (LF): latest dates without delaying the project, found in the backward pass.
• Total float (slack): how much an activity can be delayed without delaying the project end = LS - ES = LF - EF.
• Free float: how much an activity can be delayed without delaying the early start of any successor.
• Critical path: the longest path; activities on it have zero total float (with an unconstrained end date).
• Near-critical path: a path with very little float, which could become critical.

Forward and backward pass

Using the convention that the first activity starts at day 0 and EF = ES + duration:

1. Forward pass: ES of an activity = the largest EF among its predecessors (all FS). EF = ES + duration.
2. Backward pass: start from the project end, where LF = EF of the final activity. LS = LF - duration. LF of an activity = the smallest LS among its successors.
3. Float: LS - ES.

Worked example: critical path and float

Scenario. A project has these FS activities.

Step 1: list the paths.

• A-B-D-F: 4 + 6 + 5 + 2 = 17
• A-C-E-F: 4 + 3 + 7 + 2 = 16

Step 2: forward pass. A: 0-4. B: 4-10. C: 4-7. D: 10-15. E: 7-14. F: ES = max(15, 14) = 15, EF = 17.

Step 3: backward pass. F: LF = 17, LS = 15. D: LF = 15, LS = 10. E: LF = 15, LS = 8. B: LF = 10, LS = 4. C: LF = 8, LS = 5. A: LF = min(LS of B = 4, LS of C = 5) = 4, LS = 0.

Step 4: float. A: 0. B: 4 - 4 = 0. D: 10 - 10 = 0. F: 0. C: 5 - 4 = 1. E: 8 - 7 = 1.

Step 5: answer. The critical path is A-B-D-F, duration 17 days. C and E each have 1 day of total float; path A-C-E-F is near-critical.

Why the other readings are wrong. The longest path is not the one with the most activities (A-C-E-F has the same count but is shorter). Activities C and E have float, but they share it: delaying C by 1 day consumes E's float too, since they are on the same path. The sum of durations of all activities (27) is not the project duration.

Gantt charts, milestones, and schedule reserve

A bar chart (Gantt) shows activities against time; a milestone chart shows only key events; a network diagram shows logic. Schedule reserves (contingency for identified risks) are included in the schedule and baseline; management reserves of time are outside it. Buffers in critical chain scheduling protect the chain's end rather than each task: resource constraints are addressed, safety margins are pooled, and a project buffer is placed at the end of the critical chain.

Resource-constrained schedules

CPM assumes unlimited resources. Resource leveling adjusts start and finish dates to resolve overallocation and can lengthen the schedule and change the critical path. Resource smoothing adjusts activities within their float without changing the end date. Both are explained further in the resource lesson. The schedule must be checked against real resource calendars (holidays, leave, shared specialists).

5. Coordinate with other projects and operations

Few projects are isolated. The project manager identifies dependencies with other projects, programs, and daily operations, and agrees dates with their owners.

• Shared resources: a specialist split across projects may be only 40% available. Plan with actual availability.
• Operational blackout periods: a retailer will not accept a system cutover in November and December. Add these constraints as calendars.
• Interproject dependencies: record them in the schedule and the risk register; agree interface milestones and escalation points.
• Change windows: production changes may be restricted to Sunday nights; plan deployments accordingly.
• Governance: align with the portfolio or program calendars, and raise conflicts to the steering committee or PMO.

Worked example: a blackout constraint

Scenario. A bank's ledger migration needs 9 working days in the production environment. The bank forbids production changes during the last 5 business days of every quarter. The quarter ends in 15 business days, and the migration cannot start until testing finishes in 10 business days.

Step 1: compute the window. The blackout starts after business day 10 (15 - 5), exactly when testing finishes. So no production days are available before the blackout, and the migration needs 9. The blackout lasts 5 days, so the earliest compliant start is day 15, and the migration would end on day 24.

Step 2: options. Schedule the migration after the blackout (a delay of 5 working days), compress testing to start migration earlier, or split the migration across the change window and the next one.

Step 3: decide with stakeholders. Splitting risks data inconsistency; compressing testing raises quality risk. The project manager recommends scheduling after the blackout and shows the sponsor the delay, the risk comparison, and the effect on downstream milestones.

Why other choices are weaker. Starting anyway breaches an operational rule. Ignoring the blackout in the baseline would create a schedule that cannot be executed.

6. Plan releases and iterations (adaptive)

Product roadmap and release plan

The roadmap shows themes or outcomes across quarters. The release plan indicates which features are planned for which release, based on priority, value, dependencies, and team velocity. It is a forecast, not a commitment, and is updated after each iteration.

Iteration planning

At iteration planning the team selects backlog items it can complete in the time-box, based on capacity and velocity, and defines the iteration goal. Capacity accounts for holidays and non-project work: a team of 6 with 10-day iterations, with 20% of time on support, has about 6 x 10 x 0.8 = 48 person-days.

Example: release forecast

A product owner has 180 story points of must-have items. The last six iterations delivered 28, 32, 30, 26, 34, 30 points (average 30). Forecast: 180 / 30 = 6 iterations, with a range of 5.3 to 6.9 using the slowest and fastest. If the launch date falls after 7 iterations, there is buffer of one iteration, which can be used for should-have items or kept as reserve. If the launch is after 5 iterations, scope must be reduced to about 150 points, or capacity increased, with the product owner choosing what to cut.

Dependencies and cross-team planning

Large-scale agile uses joint planning events to surface dependencies. Teams visualize them on a board and agree interface milestones. Dependencies are limited by structuring teams around products or value streams where possible.

7. Common pitfalls and exam tips

• Pitfall: confusing float with reserve. Float belongs to activities; reserve is added for risk.
• Pitfall: a single-point estimate with no range. The best answer usually shows uncertainty.
• Pitfall: ignoring resource availability. A path-based schedule can be impossible if the people are unavailable.
• Pitfall: critical path with leads and lags. Include them in the pass calculations.
• Pitfall: treating the release plan as a promise. It is updated as velocity data change.

Exam tip: On calculation questions, list all paths and add up durations; the longest is critical. Check that you have used the right formula: PERT divides by 6, triangular by 3.

Exam tip: If a question gives you a conflict with another project, the best answer is early coordination with the other project manager or the PMO, with options presented to the sponsor.

Exam tip: For agile estimates, prefer relative sizing by the whole team (planning poker) over a manager assigning hours.

Exam tip: When estimating accuracy is the issue, bottom-up is more accurate but costly; analogous is quick but rough. Pick based on the stage of the project and the information available.

8. Mini case study: the regulatory launch date

Context. A project to launch a new insurance product has a fixed regulatory deadline of 31 March. The network has a critical path of 84 working days from the start date, which leaves 6 working days before the deadline. The pricing team (a shared resource) is available only 50% for the next month. A previous similar project took 98 working days. The sponsor asks whether the date is safe.

Question. What should the project manager answer and do?

Solution (commented).

1. Compare with history. The benchmark of 98 days suggests the 84-day estimate may be optimistic. Review the estimate basis, scope differences, and assumptions before replying.
2. Re-check the critical path with real availability. If pricing activities on the critical path total 20 days at full-time, 50% availability makes them 40 days, adding 20 days. The schedule becomes 104 days, exceeding the deadline by 14 days.
3. Use three-point estimates for the riskiest activities (regulatory review, pricing validation) to show the probable range, and quantify the chance of meeting the date.
4. Prepare options. Increase pricing capacity (borrow a specialist), fast track discretionary dependencies (start the documentation while pricing completes), descope non-mandatory features, or negotiate an earlier regulatory review slot. Each has cost and risk.
5. Coordinate with the other project that shares the pricing team, through the PMO.
6. Reply honestly. The date is at risk at current assumptions; here are the options, their effects, and a recommendation. Update the schedule baseline only after the change request is approved.
7. Do not promise the date based on the 84-day figure alone, or pad every task secretly.

Key terms

• Critical path: longest path, zero total float.
• Total float / free float: delay possible without delaying the end / the next activity.
• Lead / lag: overlap / delay between linked activities.
• Rolling wave planning: detailed near-term planning, high-level far-term.
• PERT estimate: (O + 4M + P) / 6.
• Analogous / parametric / bottom-up estimating: estimating from past projects / from rates / from details.
• Velocity: story points completed per iteration.
• Roadmap / release plan: high-level direction / planned feature delivery by release.
• Schedule reserve: time added for identified risks.
• Mandatory / discretionary dependency: hard logic / preferred logic.

Summary checklist

• I can match the schedule approach to the development approach.
• I can list estimating techniques and their trade-offs.
• I can compute a PERT estimate and its standard deviation.
• I can do forward and backward passes and find the critical path and float.
• I know the difference between total float, free float, and reserve.
• I coordinate schedule dependencies with other projects and operations.
• I can forecast a release from velocity and backlog size.
• I understand common estimating biases and how to counter them.

Official sources

• PMI, PMP Examination Content Outline (July 2026): https://www.pmi.org/-/media/pmi/documents/public/pdf/certifications/new-pmp-examination-content-outline-2026.pdf (opens in a new tab)
• PMI, About the new PMP exam: https://www.pmi.org/certifications/project-management-pmp/new-exam (opens in a new tab)
• PMI, Project Management Professional (PMP): https://www.pmi.org/certifications/project-management-pmp (opens in a new tab)