The Schedule and the Critical Path
Lesson 12 of 18 · 7 min read
A schedule answers one question: when will it be done, and what decides that date? To answer it, the planner breaks the work into activities, gives each a duration, and links them in order.
The building blocks
- Activity: a piece of work with a clear start and end. "Cast first-floor slab", not "structure".
- Duration: working days needed, given the crew and the method.
- Link: what must finish before something else can start. Footings before plinth beams. Plinth before columns.
- Calendar: working days, holidays, the monsoon, a weekly off.
Put these together and the software (or a careful person with paper) works out the earliest start and finish of every activity.
The critical path
The critical path is the longest chain of linked activities from start to finish. It sets the project end date. Any delay on it delays the whole job.
Activities not on the critical path have float: time they can slip without moving the finish date.
A worked example
Take the start of a G+1 house:
| Activity | Duration | Starts after |
|---|---|---|
| A Excavation | 4 days | Start |
| B Footings | 6 days | A |
| C Plinth beams | 5 days | B |
| D Underground sump | 8 days | A |
| E Ground-floor columns | 4 days | C |
- Path A, B, C, E = 4 + 6 + 5 + 4 = 19 days.
- Path A, D = 4 + 8 = 12 days.
- The critical path is A, B, C, E. The sump has 19 - 12 = 7 days of float.
If footings slip 2 days, the finish moves to day 21. Say site overheads (supervisor, watchman, hired props and shuttering) are ₹6,500 per day (illustrative). Two days of delay costs about ₹13,000, before any penalty in the contract. If the sump slips 2 days, nothing moves.
So the site engineer should protect B, C and E first: steel and shuttering ready before they are needed, and labour booked.
Tools
- Microsoft Project (.mpp) is commonly seen on building projects and with private clients. Microsoft still sells the desktop app; it retired Project Online on 30 September 2026 and has moved its web-based planning into Microsoft Planner.
- Primavera P6 from Oracle (.xer) is commonly asked for on large infrastructure and government contracts, and many clients require the programme in XER format.
- SYNCHRO 4D from Bentley and similar tools link the schedule to a 3D model for 4D simulation on BIM-led projects.
- Excel bar charts are common on small sites. They show dates but do not calculate the critical path.
Baseline and updates
The approved schedule is the baseline. Each week or month, the planner updates actual progress and compares it with the baseline. A schedule that is never updated is a wall poster, not a tool.
Many sites also use a three-week look-ahead: a short list, taken from the main schedule, of what must happen in the next three weeks and what it needs (drawings, material, labour).
What comes next
Every activity on the critical path needs material on time. Next, we follow material from the site's indent to payment.
Key takeaways
- A schedule is activities with durations, links and a calendar.
- The critical path is the longest linked chain; it sets the finish date.
- Float is how long an activity can slip without moving the finish.
- In the example, the path A-B-C-E takes 19 days and the sump has 7 days of float.
- Keep a baseline and update it; use a three-week look-ahead on site.
Verify on site
- Mark the critical activities for the next three weeks and check their material and labour.
- Update actual progress against the baseline at least once a week.
Check your understanding
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