Most superintendents can draw the Last Planner triangle on a napkin — master schedule up top, phase planning under it, lookahead, weekly work plan, daily huddle at the point. What fewer people can do is explain what actually happens in the lookahead layer that makes the whole thing work. That's the layer where a schedule stops being a wish and turns into work a crew can show up and finish. Get it right and your weekly plans hold. Get it wrong and you're running a very organized version of chaos.
The lookahead is the hinge. Below it, the master schedule tells you the story — footings by March, dry-in by June, TCO by fall. Above it, the weekly work plan is where foremen make promises to each other. The lookahead is where you find out whether next month's story is going to survive contact with reality, and it does that by doing one unglamorous job well: pulling constraints out of the work before the work is due to start.
Why the Master Schedule Can't Run the Job by Itself
The CPM master schedule is a planning tool, not an execution tool. It assumes activities start when their predecessors finish and that the resources show up on cue. On paper, drywall follows rough-in inspection and that's that. On site, drywall follows rough-in inspection if the inspector passed it, if the insulation's in, if the board got delivered to the right floor, if the framer came back to fix the two walls that were out of plane, and if the hangers aren't stuck on another job across town.
Every one of those "ifs" is a constraint, and the master schedule is blind to all of them. That's not a knock on CPM — it's the wrong altitude for the question. You don't manage a delivery three days out with a Gantt bar that was drawn eight months ago. The Last Planner System exists because someone finally admitted that the plan and the work are two different things, and you need a process that connects them. The lookahead is that process.
The Lookahead's Real Job: Screening Constraints
Take every activity that's going to hit the schedule in the next few weeks and run it through the same set of questions. This is the make-ready process, and it's the entire point:
- Predecessors — is the work in front of this actually going to be done, and done to a standard the next trade can build on? Not "scheduled to be done." Done.
- Materials — ordered, confirmed, and staged where the crew needs them. A delivery sitting on the ground floor when the work is on six is not "ready."
- Information — is there an open RFI, a pending ASI, a detail nobody's resolved? Unanswered questions stop work as hard as missing steel.
- Equipment — lift, hoist, pump, crane time booked and available in that window.
- Labor — the right crew, the right size, the right skills, actually assigned to this scope and not double-booked.
- Space and access — can the crew physically get in and work without stacking on top of another trade in the same room?
- Permits and inspections — signed off, or scheduled far enough ahead that the inspector isn't the thing you're waiting on.
An activity that clears all of these is made ready. Everything else is a problem you now have weeks to solve instead of a fire you'll be fighting the morning it's due. That head start is the whole value. A constraint you find during the lookahead is a phone call. The same constraint found at the daily huddle is a crew standing around getting paid to wait.
Should, Can, Will: The Three Words That Matter
Lean scheduling talks about work moving from "should" to "can" to "will," and it's worth being precise about the difference because that's where most weekly plans go wrong.
Should is what the master schedule says needs to happen this period. It's the demand. Can is the subset of "should" that's actually made ready — constraints cleared, verified. Will is what the foreman commits to at the weekly meeting. The cardinal rule: you only commit to "can" work. The failure mode that wrecks reliability is pulling commitments straight from "should" — copying next week off the master schedule bar and calling it a plan. You're now promising work you haven't verified is buildable, and you'll miss, and your crews will learn that the weekly plan is fiction.
When a foreman puts something on the weekly plan, the honest question behind it is: "Is there any reason, that I know of right now, why this crew can't finish this scope this week?" If the answer is "well, we're still waiting on the inspection" — that's not a commitment, that's a hope. Kick it back to the lookahead until the constraint's gone.
Match the Horizon to the Lead Time
There's no magic number of weeks for a lookahead. The right window is however long it takes to clear your longest routinely-recurring constraint. Different constraints need different runways:
- Long-lead materials — switchgear, elevators, custom glazing, structural steel can run 8, 12, 20 weeks or worse. These don't belong in the lookahead at all when they're first ordered; they live in phase planning and procurement logs. But the lookahead has to reach far enough to catch the delivery and confirm it before the install crew is scheduled.
- RFIs and design clarifications — figure two to four weeks for a real answer through the full loop, longer if it touches multiple design disciplines. If your lookahead is only two weeks, you're finding out about missing information the same week you needed to build.
- Equipment and rentals — a week or two for most gear, more for a crane pick that needs a plan and a permit.
- Predecessor completion and labor — usually visible and resolvable inside the near two weeks.
A three-week window is the practical floor for most interiors and fit-out work. Six weeks is common on structure and MEP-heavy jobs where information and long-lead deliveries dominate. Some teams run a hybrid — a six-week horizon for procurement and inspection visibility, worked in detail only in the front three. The point is to size the window to your actual lead times, not to a round number that sounds tidy.
Build a Workable Backlog So a Bad Day Doesn't Cost You a Week
Here's a concept the original triangle diagram never shows you, and it's the one that separates crews that stay productive from crews that stand around. A workable backlog is made-ready work held in reserve — scope that's fully cleared but not on this week's committed plan. When the primary plan hits a snag (and it will — the inspector's late, the delivery's short, a crew's out sick), the foreman reaches into the backlog and keeps people working instead of sending them home or letting them find their own busywork.
On a well-run job you want a couple of days of workable backlog per crew sitting in reserve at any time. It absorbs the normal variation that every project has. Without it, every hiccup upstream translates directly into idle labor downstream, and idle labor is the most expensive thing on your site. The lookahead is where that backlog gets built — every activity you make ready early that you don't need immediately becomes cushion.
Every Constraint Needs a Name and a Date
A constraint list without owners is just a list of things to feel bad about. In the lookahead meeting, every open constraint gets three things attached to it:
- An owner — one name, not a company. "The mechanical sub" doesn't chase an RFI; a person does. It might be the GC's PM, a specific foreman, the architect, the inspector, or a supplier's rep.
- A need date — the date the constraint has to be gone by, working backward from when the activity is scheduled. Not the date it'll probably clear. The date it must.
- A status — open, in progress, resolved — updated whenever it changes, not just at the weekly meeting.
This is where a purpose-built tool earns its keep over a whiteboard or a spreadsheet that lives on one laptop. When your lookahead lives in something like LookAheadWall, the constraints attach to the activities visually, the whole team sees the same status from the field, and made-ready work is obvious at a glance — you're not rebuilding the picture from scratch every Monday. The discipline still has to come from you, but the tool keeps everyone looking at the same reality.
Read PPC Backward Into the Lookahead
Percent Plan Complete — the share of weekly commitments you actually finished — is the scoreboard, but the score isn't the useful part. The reasons for the misses are. Every failed commitment should get a reason code, and the pattern in those codes points straight back at what's broken in your lookahead:
- Misses caused by missing materials or unfinished predecessors mean your constraint screening is weak — that work got committed before it was truly ready.
- Misses caused by long-lead items showing up late mean your horizon is too short to catch them.
- Misses on work that "should have been fine" often mean commitments are coming from the master schedule instead of from made-ready work.
Chase a PPC of 100% and you'll get it by having foremen commit to almost nothing — a useless number. A healthy job usually lands somewhere in the 70s or 80s early and climbs as the make-ready process matures. What you're really watching is the reason codes trending toward zero root causes you control. That's the lookahead getting better.
How the Connection Breaks in Practice
When the lookahead and the Last Planner logic drift apart, it looks like this, and you've probably seen every one:
- The lookahead as a wish list — it shows what should happen, nobody screens constraints, and it's really just the master schedule chopped into three-week slices.
- Weekly plans pulled from the Gantt — commitments come off CPM bars, not from verified made-ready work, so the plan looks organized and misses constantly.
- A static lookahead — built once, printed, taped to the trailer wall, never updated as conditions change. By Wednesday it's fiction.
- Constraints with no owners — everybody sees the problem, nobody's chasing it, and it's still open the day the work was due.
The fix for all four is the same discipline: screen every activity on the way into the window, assign every constraint a person and a date, commit only made-ready work, and update the thing continuously instead of treating it as a document you produce for a meeting.
Run the Meeting So the Two Layers Stay Connected
The weekly lookahead-and-work-planning session has a rhythm that keeps the layers stitched together. Review last week first — calculate PPC, walk the misses, capture the reasons, and treat them as learning, not blame. Then walk the lookahead: update every constraint's status, flag new ones that surfaced as work progressed, and confirm which activities have gone made-ready. Then, and only then, build next week's plan by pulling committed work out of the made-ready pile. Close by coordinating the trade handoffs so nobody's promising to work in a room another crew hasn't left yet.
That sequence is the connection, made concrete. The master schedule sets the demand. The lookahead converts demand into made-ready supply. The weekly plan spends that supply as reliable commitments. Break any link and reliability leaks out — usually silently, until a foreman quietly stops believing the plan and starts running his own crew off gut feel. Keep the links tight, and the schedule on the wall becomes something your trades actually trust. That trust is the real product, and it's worth more on a jobsite than any single milestone.