Critical path

Critical Path vs Critical Chain: A Shutdown Float Example

Short answer

The critical path is the longest continuous sequence of activities that sets the shutdown finish date, and float is how long an activity can slip without moving it. Critical chain also counts resource dependencies and uses buffers. This page works one example by hand and gives a float calculator.

How MaintWiz helps: Float and critical path change daily; the plan has to follow. The MaintWiz shutdown module puts the whole shutdown on a Gantt chart with the critical path, float and baselines, so you can see what moves the finish date. See the module · Get the Gantt template

By Jai Balachandran · Published 18 October 2026 · Last reviewed 18 October 2026

See your shutdown plan in MaintWiz Try the float calculator

What MaintWiz adds:Gantt with critical path and floatBaselines show what movedFloat flag at your limitOne plan from portfolio to task

Float

What are the critical path and float in a shutdown?

The critical path is the longest continuous sequence of activities that sets the finish date, and float is how long an activity can slip without moving that date; activities on the critical path have zero float. ¹

Network of seven activities: critical path A, D, E, F over 9 days with zero float; B, C and G each carry 3 days of float — **Critical path and float, worked example.** Seven activities from the table below: A, D, E and F form the critical path of 9 days with zero float, while B, C and G each carry 3 days of float. Each box shows duration, early start and early finish.

Check the orange chain first: any slip there moves the finish day for day. The 3 days of float on B, C and G are shared along that chain, so use them on B and none is left for C or G, which is why float needs watching every day.

A free Excel file for this page: Schedule with Gantt template (.xlsx).

The US GAO schedule guide describes the critical path as the longest continuous sequence of activities and float as the amount an activity can slip without delaying a later date; float is not contingency. ¹ This page works a small example by hand so you can see how the numbers arise. The full method, with the Gantt chart and resource loading, is in the shutdown scheduling guide.

The worked example

Worked example: nine activities, durations in days
ID	Activity	Days	After	Early start	Early finish	Late start	Late finish	Total float
A	Isolate and drain	2	none	0	2	0	2	0 (critical)
B	Remove pump	1	A	2	3	5	6	3
C	Overhaul pump	3	B	3	6	6	9	3
D	Open vessel	2	A	2	4	2	4	0 (critical)
E	Clean vessel	3	D	4	7	4	7	0 (critical)
F	Inspect vessel	2	E	7	9	7	9	0 (critical)
G	Reassemble pump	2	C	6	8	9	11	3
H	Reassemble vessel	2	F	9	11	9	11	0 (critical)
I	Leak test	1	G, H	11	12	11	12	0 (critical)

Day123456789101112

A Isolate and drain

B Remove pump

C Overhaul pump

D Open vessel

E Clean vessel

F Inspect vessel

G Reassemble pump

H Reassemble vessel

I Leak test

The finish is day 12. The critical path is A to D to E to F to H to I: any delay to one of those activities delays the restart by the same amount. The pump activities B, C and G each have 3 days of total float, and because they are a chain, the 3 days are shared: using it all on B leaves none for C and G. Late finish minus early finish gives total float for each activity.

Calculator

How do you calculate float?

Total float is the late start minus the early start, or equivalently the late finish minus the early finish; early dates come from a forward pass through the network and late dates from a backward pass from the finish.

MaintWiz: float map by unit and discipline, coloured by least float, with today line and driving chain — **Float map.** Rows are units and disciplines, columns are days, and each cell's colour is the least float of the work running then: red critical, orange near-critical, blue shades for float to 10, 10 to 20 and over 20 days, green complete. A dashed line follows the driving chain.

Look for red and orange cells and follow the dashed line: that is where a slip moves the finish. The long pale-blue runs are work with more than 20 days of float, which can wait while crews go to the critical chain.

More tools are on the shutdown calculator tools page. The free Excel to Gantt tool runs this calculation on a whole task list.

Early start is the latest early finish among the predecessors. Early finish is early start plus duration. Late finish is the earliest late start among the successors, and the last activity's late finish equals the project finish. The calculator below applies the same arithmetic to one activity. The default values are those of activity C above, which has three days of float.

Try it: compute total float

Enter an activity's early start, duration and late finish, in days. The calculator gives early finish, late start and total float. Nothing is sent or stored.

Early start (day)Duration (days)Late finish (day)

Early finish6

Late start6

Total float3

StatusHas float

Software

What does MaintWiz do for critical path and float?

MaintWiz computes the critical path and float for the shutdown schedule today and flags activities as their float runs down; it also provides critical chain analysis, what-if scenarios and Monte Carlo finish confidence.

See the shutdown module Book a demo

Also in the module: critical chain analysis, what-if scenarios, Monte Carlo confidence of finish.

What the shutdown module covers

Gantt chart with the critical path and float for every activity
A flag when float falls to a limit you set
Baselines that show what moved against the plan
Resource availability by trade and week across projects
Import and export with Excel and Microsoft Project XML, with interoperability with Primavera P6

Proof

What MaintWiz customers report

Global tyre manufacturer, seven plantsMaintenance cost down 17%, mean time between failures up 10 to 15%, and about 15% less effort on work orders through automated work order creation.Read the case study India's leading paint producer, multiple plantsOne maintenance system across plants, integrated with SAP and DCS, with contractor work order approvals 95% faster through a mobile app.Read the case study

Results from MaintWiz customers across maintenance operations.

Critical chain

What is the difference between critical path and critical chain?

The critical path considers only the logic between activities, while critical chain also counts resource dependencies and moves schedule safety into buffers; a 1997 practitioner paper puts the difference as including resource dependencies and never changing. ²

Critical path and critical chain compared
Question	Critical path method	Critical chain method
What sets the finish?	The longest sequence of dependent activities	The longest sequence once resource dependencies are included
How is uncertainty handled?	Float and, separately, contingency	Aggregated into buffers at the end of paths
How is progress watched?	Float erosion on each activity	Consumption of the project and feeding buffers
What do the tools support?	Schedule tools describe their engines as critical-path based	Specialized methods and add-ons

The paper describes a project buffer protecting the finish and feeding buffers protecting the critical chain where paths merge. ² It is an advocacy paper from a practitioner, so use it for the definitions only, not for its performance claims. Mainstream schedule tools are built on the critical path method; Oracle says its Primavera P6 uses a critical-path algorithm, and Microsoft Project shows critical tasks in red on the Gantt chart. ^3,4

In a shutdown, resources are often the real constraint: one crane, one crew of welders, one clean room. A critical path schedule that ignores this can be late in practice even when its float looks healthy. The usual practical answer is to resource-load the schedule and level the peaks, which the GAO guide also expects. ¹

The comparison table is a simplified summary for orientation. Critical chain is a separate method with its own training.

In practice

Which should a shutdown use?

Most shutdowns run on the critical path method with resource loading and visible float, and they treat critical chain buffers as an advanced option rather than a starting point.

MaintWiz: driving critical path and the paths behind it, box colour by float, dashed baseline windows — **Driving path and the paths behind it.** Each box is a work package coloured by its path's float, with a dashed outline where it sat in the baseline. Path 1 carries zero float to the finish on 27 April, and path 2 shows -1.5 days of float.

Start with the path that ends at the finish line: it drives the date. Negative float on a second path means that path is already late and will become the driver unless it is recovered, so it tells the shutdown manager where to put effort first.

A resource-driven example is in mining mill reline shutdown planning. Refueling outages are a planned-outage example: nuclear refueling outage planning. A boiler-led off-season with a fixed end date: sugar mill off-season maintenance. Emergent work on the critical path, worked through: shutdown case study planned vs actual.

What to do in a shutdown
Situation	Practical approach
You have a logic-linked schedule with durations	Find the critical path and watch float every day; start recovery when a critical activity slips
A crew or machine is the bottleneck	Resource-load the schedule, level the peaks and treat the resource-driven sequence as part of the critical path
Estimates are padded in every task	Challenge task estimates against past actuals; keep one explicit contingency rather than hidden padding
You want critical chain buffers	MaintWiz supports critical path with float, Monte Carlo confidence of finish and critical chain analysis in the shutdown module

See the scheduling guide for the method and the schedule delays guide for recovery. Contingency sizing is in the budget guide.

Definitions

What are the critical path and float?

The HHS earned value glossary defines the critical path as the path of dependent tasks with the longest elapsed time, and the GAO schedule guide defines float as the time an activity can slip without delaying a later date. ^5,1

Critical path terms and where they are defined
Term	Definition	Source
Critical path	The path through a network of dependent tasks with the longest elapsed time; any delay to a task on it delays the finish by the same amount	HHS earned value glossary, GAO schedule guide
Float	The time an activity can slip without delaying a later date; float is not contingency	GAO schedule guide
Critical chain	A method that adds resource dependencies and buffers to the logic	Leach critical chain paper

FAQ

Frequently asked questions

What is the critical path in a shutdown?

The longest continuous sequence of activities that sets the restart date. A delay to any activity on it delays the finish by the same amount. ¹

What is float?

The time an activity can slip without delaying a later activity or the finish. Total float is late start minus early start. Float is not contingency. ¹

Why can float be shared?

Activities in a chain share the float of the chain: if the first one uses all of it, the others have none. In the worked example B, C and G share three days.

What is critical chain?

A method that adds resource dependencies to the logic and moves schedule safety into buffers at the end of paths. ² It is a different method from the critical path method.

Should a shutdown use critical chain?

Most plants start with a logic-linked, resource-loaded critical path schedule and daily float tracking. Critical chain is an advanced option that needs a trained team and tool support.

Does MaintWiz support critical chain analysis?

Yes. MaintWiz shows the critical path and float and supports critical chain analysis.

How often should you check float?

Daily during the stop, in the daily meeting. See progress tracking.

Where is the full scheduling method?

In the shutdown scheduling guide.

Sources

Put your shutdown schedule in one plan

Book a demo and bring your shutdown schedule. We will show how the module handles the critical path, float and baselines.

See your shutdown plan in MaintWiz Get the Gantt template

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