Construction schedules fail less because crews work slowly than because promises are broken: the materials are not there, the drawings are not answered, or the trade before has not finished. The Last Planner System, a core Lean construction practice, tackles this by planning with the people who do the work and committing only to work that is ready.
This guide covers the levels of the system, how to measure percent plan complete (PPC) and the reasons for misses, and a worked example in which PPC rises from about 65% to about 83% after the team starts screening the lookahead for constraints.
Before You Start
Why Planning Reliability Matters
Trades Wait on Each Other
A task that is not finished on time delays the trade that needs its output, and the delay ripples down the schedule.
Schedules Assume Promises Are Kept
Traditional schedules push work at crews whether or not the prerequisites are ready. Unreliable promises make everyone add buffers.
Constraints Are Preventable
Missing materials, drawings, and access are usually known days ahead. Finding them early gives time to remove them.
What Gets Measured Improves
Percent plan complete makes reliability visible, and the reasons for misses show what to fix.
What the Last Planner System Is
The Last Planner System was developed by Glenn Ballard and Greg Howell and is a core practice of Lean construction. It focuses on making and keeping reliable commitments between the people who actually plan and do the work, the "last planners" such as foremen and superintendents. Its levels connect the big plan to the weekly plan:
| Level | What it is | Who takes part |
|---|---|---|
| Master schedule | Milestones and overall duration for the project | Owner, general contractor, key trades |
| Phase (pull) plan | A phase planned backward from its end date, with trades stating what they need from each other | The trades working in that phase |
| Lookahead plan (often 6 weeks) | Activities scheduled to start soon, screened for constraints and made ready | Superintendent, foremen, coordinators |
| Weekly work plan | Commitments the crews make for the coming week, only for work that is ready | Foremen and crews |
| Learning | Measure percent plan complete (PPC) and the reasons for misses, then act on them | Everyone |
Percent Plan Complete and Reasons for Variance
PPC is the number of weekly assignments completed as promised divided by the number of assignments planned, expressed as a percentage. It measures how reliable the promises are, not how fast the work goes. Each missed assignment is given a reason for variance, such as materials not delivered, prerequisite work incomplete, design information missing (an RFI outstanding), crew or labor shortage, equipment, weather, or owner or inspector delay. A Pareto chart of reasons shows where to intervene. See the Pareto Analysis Guide.
PPC is a learning measure for the team, not a tool to blame foremen. Publishing it by crew as a ranking tends to encourage padding the plan with easy tasks.
Worked Example: Eight Weeks of PPC
A general contractor tracks PPC on the interior fit-out of a mid-size building. The figures are illustrative.
| Week | Planned | Completed | PPC |
|---|---|---|---|
| 1 | 40 | 26 | 65.0% |
| 2 | 42 | 28 | 66.7% |
| 3 | 38 | 26 | 68.4% |
| 4 | 41 | 31 | 75.6% |
| 5 | 44 | 34 | 77.3% |
| 6 | 40 | 33 | 82.5% |
| 7 | 43 | 36 | 83.7% |
| 8 | 42 | 35 | 83.3% |
In weeks 1 to 3, 40 assignments were missed. The reasons were: materials not on site (14), prerequisite work incomplete (10), design information or RFI outstanding (7), labor shortage (5), and other (4). Materials and prerequisite work together account for 24 of 40, or 60%. The team responds by adding a weekly constraint review to the lookahead: each activity starting within three weeks is checked for materials, information, access, and prerequisite work, and it is not committed to a weekly plan until it is ready.
From week 4 the team commits only to ready work. Average PPC in weeks 1 to 3 was about 67%, and in weeks 4 to 8 about 80%. The team did not ask crews to work harder. It changed what they were asked to promise. Watch for a trap, though: PPC can be raised by promising less, so the team also tracks the number of assignments completed and overall schedule progress.
Track your own weeks and reasons with the Percent Plan Complete Tracker, and plan the six-week lookahead in the Last Planner Work Plan Template.
Self-Assessment Questions
- Do the people who do the work take part in planning it?
- Do we screen lookahead activities for constraints before committing to them?
- Do we record a reason for every missed assignment, and act on the top reasons?
- Do we use PPC to learn, not to rank or blame?
- Do we look at schedule progress as well as PPC?
Common Mistakes
Committing to Work That Is Not Ready
A commitment to a task with a missing constraint is a promise likely to be broken. Make work ready first.
Recording Reasons Vaguely
"Other" tells you nothing. Use a short, agreed list of reasons and keep it consistent.
Gaming PPC
Promising only easy tasks raises PPC without improving flow. Watch the total work completed and the schedule.
Running It as a Superintendent-Only Exercise
Reliable promises come from crews planning their own work. Involve foremen from the start.
Lean Construction and the Last Planner System: Frequently Asked Questions
What is the Last Planner System?
The Last Planner System is a Lean construction planning and control method developed by Glenn Ballard and Greg Howell. It links the master schedule to weekly commitments through phase pull planning, a lookahead plan screened for constraints, and weekly work plans made by the people who will do the work, and it measures reliability with percent plan complete.
What is percent plan complete (PPC)?
PPC is the number of weekly assignments completed as promised divided by the number planned, expressed as a percentage. It measures how reliable the team's commitments are. Each missed assignment is given a reason for variance so the team can remove the most common causes.
Does a high PPC mean the project is on schedule?
Not necessarily. PPC measures reliability of promises, and it can be raised by promising less. Use it with measures of work completed and progress against the schedule, and look at the reasons for variance to learn what is disrupting the work.
Sources and Further Reading
- Glenn Ballard, The Last Planner System of Production Control, PhD thesis, University of Birmingham, 2000.
- Lean Construction Institute, Last Planner System resources.
- Gregory A. Howell and Glenn Ballard, work on lean project delivery and reliable promising.
- Hal Macomber and Gregory Howell, Linguistic Action: Contributing to the Theory of Lean Construction.