What Is Float in a Construction Program?
Float is the amount of spare time an activity in a construction program has before a delay to it starts causing problems elsewhere. Total float is how much an activity can slip without pushing out the overall project completion date. Free float is the narrower measure — how much it can slip without delaying the very next activity that depends on it. Activities on the critical path have zero total float by definition: any delay to them is a delay to the whole job, which is exactly why the critical path gets so much attention from planners, estimators and anyone managing program risk.
Key takeaways
- Float is the spare time an activity can be delayed without causing a knock-on problem elsewhere in the program.
- Total float measures delay tolerance against the overall project finish date; free float measures it against just the next dependent activity.
- Critical path activities have zero total float — any delay to them delays the whole project finish date.
- Float is calculated from the program logic — durations and dependencies — not estimated by eye; it comes out of a proper critical path analysis.
- Understanding float helps a builder or estimator judge which delays actually threaten the completion date and which ones can be absorbed without consequence.
What is float, in plain terms?
Float — sometimes called slack — is the buffer of time built into a construction program between when an activity could start and when it actually has to start to keep the job on track. If an activity has two weeks of float, it can begin up to two weeks late without anything downstream being affected.
Float isn’t a fixed property of a task — it comes out of the logic of the whole program: how long each activity takes, and which activities depend on which others finishing first. Change one duration or one dependency, and float shifts everywhere else in the network.
In plain terms
Float is how much room a task has to run late before its delay becomes everyone else’s delay.
Total float vs free float
Total float and free float both measure spare time, but against different points of reference, and mixing them up is a common source of confusion in program discussions.
Total float looks all the way to the end of the project — it’s how much an activity can slip before it delays the project completion date. Free float looks only as far as the next task in the chain — it’s how much an activity can slip before it delays the start of whatever comes immediately after it.
| Total float | Free float | |
|---|---|---|
| Measures delay against | The overall project finish date | The start of the very next dependent activity |
| Typically | Larger than or equal to free float | Smaller than or equal to total float |
| Used to assess | Whether the project completion date is at risk | Whether the immediate next task is at risk |
| Zero on the critical path? | Yes, always | Usually, though not in every case |
Why critical path activities have zero float
The critical path is the longest chain of dependent activities through the whole program — the sequence that adds up to the project’s total duration. Every activity on that chain has zero total float, because there is no spare time anywhere along that particular path: a delay to any one of them pushes the finish date out by the same number of days.
Activities off the critical path have some float precisely because there’s an alternative, shorter path running in parallel — the slower path can absorb a delay without becoming the new bottleneck, at least up to the amount of float it holds.
How planners and estimators use float
Float isn’t just a scheduling curiosity — it’s a practical tool for deciding where attention, resources and risk management actually need to go.
- Prioritising site supervision and resourcing toward critical path activities, where a delay has real consequences.
- Deciding where labour or plant can be reallocated temporarily without threatening the completion date.
- Assessing whether a client-caused delay or a variation genuinely affects the program, or whether the affected activity had enough float to absorb it.
- Supporting or challenging an extension of time claim — a delay to an activity with float remaining is a harder case to argue than a delay to a critical path item.
- Negotiating program changes during a job, since moving a low-float activity carries far more risk than moving one with weeks of float in hand.
Common float misunderstandings
Float causes more disputes than most other program concepts, usually because the term gets used loosely rather than calculated properly.
- Assuming every task has some float — critical path items, by definition, have none.
- Treating float as a contingency buffer owned by whoever holds it, when who “owns” float is often a genuine, contract-specific question in a delay dispute.
- Confusing float with contingency time added to the whole program — float lives inside the existing program logic, contingency is added on top of it.
- Not recalculating float after a variation or a program revision, so the critical path analysis being relied on is already out of date.
Where My Trade Hub fits alongside your program
My Trade Hub doesn’t replace your construction program or critical path scheduling software — float and the critical path are program-management concepts, not something a tender preparation platform calculates for you.
What it does do is give some of that time back before the program even starts: by automating quantity takeoff from your plans and applying your editable rates library automatically, preparing a priced tender is 60–75% faster than doing it manually — so the time pressure that eats into program float before a job even starts is one less thing working against you.
Frequently asked questions
What does float mean in a construction program?
Float is the amount of time an activity can be delayed without causing a knock-on delay elsewhere — either to the overall project finish date (total float) or to the very next activity that depends on it (free float).
What is the difference between total float and free float?
Total float measures how much an activity can slip before it delays the whole project’s completion date. Free float measures the narrower case — how much it can slip before it delays just the next dependent activity in the chain.
Why do critical path activities have zero float?
The critical path is the longest chain of dependent activities in the program, adding up to the project’s total duration. There’s no spare time anywhere along that chain, so a delay to any activity on it delays the whole project by the same amount.
Is float the same as contingency?
No. Float is spare time that already exists inside the program’s logic and dependencies. Contingency is extra time deliberately added on top of the program to absorb unknown risks — the two are calculated and used differently.
How is float used in an extension of time claim?
Whether an activity had float remaining when a delay occurred is often central to an extension of time claim — a delay to an activity with float left in hand is a weaker case for extra time than a delay to a critical path activity with none.
Does float change during a job?
Yes. Float comes out of the program’s durations and dependencies, so any variation, delay or program revision can shift float throughout the network — which is why the critical path analysis needs to be recalculated, not assumed to still hold.
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