In brief: Primavera P6 scheduling means building and running a project’s critical path method (CPM) schedule in Oracle Primavera P6. The schedule is made of activities, logic links, calendars and a small number of constraints. P6 calculates early and late dates and float from that logic, and the result becomes the baseline programme the engineer approves and the record every update and delay claim is measured against. A P6 schedule is only as good as its logic, so most of the work is in structure and checks, not in the software.
This guide explains what P6 scheduling involves on a construction project, how the scheduling calculation works, what contracts usually require, the checks a reviewer will run, and when it makes sense to bring in a specialist scheduler.
Contents
- What Primavera P6 is
- The parts of a P6 schedule
- How P6 calculates the schedule
- What contracts ask for
- Updating the schedule
- Checks a reviewer will run
- P6 or Microsoft Project?
- When to use a specialist scheduler
- Questions we are often asked
What Primavera P6 is
Oracle Primavera P6 is project scheduling software used on large construction, infrastructure, energy and oil and gas projects. It comes in two main forms:
- P6 Professional: a desktop application, used by most planners for day-to-day scheduling.
- P6 EPPM: the web-based enterprise version, used by owners and large contractors that manage many projects in one database.
Both store the schedule in a database. Schedules are usually exchanged as XER files, which is why a client or engineer will ask for “the XER” with each submission. If the other party works in Microsoft Project, see our guide to converting XER to MPP.
The parts of a P6 schedule
| Element | What it does |
|---|---|
| Enterprise project structure (EPS) | Groups projects in the database, for example by client or region. |
| Work breakdown structure (WBS) | Breaks the project into areas, systems or deliverables. It drives summary reporting. |
| Activities | Units of work with a duration, a calendar and, where needed, resources. Milestones mark key dates. |
| Relationships | Finish-to-start, start-to-start, finish-to-finish and start-to-finish links, with or without lag. They carry the logic. |
| Calendars | Working days, hours and holidays. Different trades or areas often need different calendars. |
| Constraints | Fixed dates imposed on activities. Use them sparingly, because they override logic. |
| Activity codes | Tags such as area, trade, phase or responsible party, used for filtering and layouts. |
| Resources and costs | Labour, equipment and cost loading, needed for histograms, S-curves and earned value. |
A clear activity ID convention makes all of this easier to review. Our note on activity ID coding in P6 gives a practical scheme.
How P6 calculates the schedule
When you press F9 (Schedule), P6 runs a forward and backward pass through the network from the data date:
- The forward pass gives each activity its early start and early finish.
- The backward pass gives its late start and late finish, working back from the project finish or a must-finish-by date.
- Total float is the difference between late and early dates. Activities with the lowest float, or on the longest path, form the critical path.
Several schedule options change the result, so they should be agreed and recorded with the baseline:
- Retained logic or progress override: how P6 treats activities that started out of sequence. Retained logic is the usual choice for construction.
- Critical activities: defined by total float less than or equal to a value, or by the longest path.
- Total float calculation: finish float, start float or the smaller of the two.
- Calendar for scheduling relationship lag: the predecessor’s, the successor’s, the 24-hour or the project default calendar.
For more on reading the result, see critical path analysis in P6 and negative total float.
What contracts ask for
Most construction contracts set out what the programme must contain and when it must be submitted. Examples:
- FIDIC 2017 (Red, Yellow, Silver), Sub-Clause 8.3: an initial programme within 28 days of commencement, with stated content, and a revised programme when the existing one no longer reflects actual progress.
- NEC4, clauses 31 and 32: a programme with set content, accepted by the project manager, and revised programmes at the intervals stated in the contract.
- US public and federal work: specifications often call for a resource- or cost-loaded CPM schedule in P6 with monthly updates and a narrative.
Owners and engineers in the Gulf commonly require P6 by name and specify the XER format, the WBS levels, the activity coding and the maximum activity duration. Reading these requirements before building the schedule saves a rejected first submission.
Updating the schedule
An update records what has happened and forecasts what is left. At each data date:
- Enter actual start and finish dates for activities that started or finished.
- Update progress on activities in progress, using the agreed percent complete type, and check their remaining duration.
- Add any new work, changes or delay events as activities with logic, and record them in the narrative.
- Move the data date and reschedule.
- Compare the result with the baseline and the previous update, and explain the main changes to the critical path and the forecast finish.
Updates are the main evidence in a later delay claim. A record of what changed and why, issued each period, is worth far more than a reconstructed one. Our guide to finding delayed activities in P6 shows how to spot slippage early.
Checks a reviewer will run
Engineers and owners usually test a submitted schedule against a set of quality checks. The DCMA 14-point assessment is the most widely used. The main checks are:
- Open ends: activities with no predecessor or no successor, other than the start and finish milestones. See dangling activities in P6.
- Leads (negative lags) and long lags.
- Relationship types: mostly finish-to-start.
- Hard constraints that stop the logic driving dates.
- High float and negative float.
- Long durations (often anything over 44 working days).
- Invalid dates: actuals after the data date, or forecasts before it.
- Resources: whether activities carry the resources or costs the contract asks for.
- Missed tasks and a critical path test: does delaying a critical activity move the finish date?
Running these checks yourself before submission is the quickest way to avoid a “revise and resubmit”.
P6 or Microsoft Project?
| Primavera P6 | Microsoft Project | |
|---|---|---|
| Typical use | Large, multi-party projects; often required by contract | Smaller projects, internal planning |
| Data | Database with multiple projects, baselines and users | Mostly single files (MPP) |
| Calendars and float | More scheduling options, multiple float paths | Fewer options |
| Exchange format | XER or XML | MPP or XML |
If the contract names P6, use P6. Converting later loses calendars, codes and settings, and the converted file will not be accepted as the contract programme.
When to use a specialist scheduler
Many contractors keep a planner in-house. A specialist is worth considering when:
- the baseline programme has been rejected, or the contract deadline for it is close;
- the project is large, phased or has many interfaces, and the in-house team is stretched;
- a recovery or acceleration programme is needed;
- delays are building up and the updates need to be in a state that can support an extension of time claim.
Solvix prepares and reviews P6 programmes for contractors and owners, including baseline programmes in Dubai and the UAE, Saudi Arabia and Egypt, CPM scheduling in the United States and P6 programming in Australia. A typical baseline programme takes one to two weeks. See our baseline schedule service, or send a short brief through the contact page.
Questions we are often asked
Is P6 scheduling the same as CPM scheduling?
CPM is the method; P6 is the software that applies it. A P6 schedule is a CPM schedule built and calculated in Primavera P6. For a step-by-step build, see how to create a CPM schedule in P6.
How many activities should a construction schedule have?
Enough to show the critical path and the work of each trade and area at the level the contract asks for. For a mid-size building that is often a few hundred to a few thousand activities. Too few hide the logic; too many make updates impractical.
What is an XER file?
The native export format of Primavera P6. It contains the project’s activities, logic, calendars, codes and settings, so another P6 user can import and check it.
How often should a P6 schedule be updated?
Usually monthly, or as the contract states. Fast-moving or recovery work may need weekly updates of the near-term activities.
