Professional guide · Yaakov Avital, quantity surveyor and registered building technician · updated 25 October 2026

Construction schedule: from quantities to outputs, from durations to a Gantt chart and the critical path

A construction schedule is built from the same quantities as the bill of quantities (BOQ): for each activity you calculate how many working hours it needs, divide by the size of the crew, and get a duration. Then you link the activities in the order in which they have to happen, and you get a Gantt chart, and in it the critical path, the chain in which any delay delays the whole project. I have experience in building schedules from quantities, from my final project in construction management to contractors' tenders.

The formula: quantity times norm, divided by crew

The duration of an activity in working days equals the quantity, times the working hours per unit, divided by the number of workers times the working hours per day. The norm, hours per unit, is also called an input (a labour constant); its inverse, units per hour, is called output or productivity. The full explanation is on the page construction inputs.

The example below uses illustrative norms from the study material of my final project. On every project the norms are set again according to the crew, the method and the conditions.

Look at the first row: 1,260 hours divided by 36 crew hours a day gives 35 days. Add a fifth formwork carpenter and the duration drops to 28 days. That is exactly the choice the contractor makes: more crew, less time, and a different labour cost.

Dependencies between activities and the critical path

An activity does not start whenever you like. There are dependencies: rebar fixing after formwork, pouring after rebar fixing, and stripping the formwork only after the concrete has reached its strength. Some dependencies allow overlap: steel fixers can start on the first half of the slab while the formwork carpenters are still on the second half. The critical path is the longest chain from the start of the project to its end. An activity that is not on the path has float, time by which it can be moved without delaying completion.

A worked example: finding the critical path

Six activities, with durations in working days, as an illustration. The early start of each activity equals the latest finish among the activities it depends on.

The diagram in short: A → B → C → D → F, and in parallel A → E → F. The first chain takes 100 working days, and it is the critical path. Railing fabrication has a float of 45 days: it can start that much later without delaying completion. But if the supplier is more than 45 days late, the railings enter the critical path and completion moves. So following up suppliers is part of the schedule, not an add-on to it.

A small Gantt chart in a table

A Gantt chart is simply a timeline: each row is an activity, each column is a period. Here is a shortened Gantt chart for a private house with a basement, in months, for illustration only:

From working days to months: a calendar month has fewer working days than calendar days. Saturdays, holidays and rain days come off the count, and in my final project I prepared a separate sheet for the conversion to working days. Whoever skips this step gets a schedule that looks good on paper and runs late on site.

Five common mistakes in a construction schedule

• Durations without quantities: "three months for the frame" with no square metres of formwork and tonnes of rebar behind it cannot be checked.
• No rain days or holidays: a whole winter in the schedule without a single rain day is an optimistic schedule.
• No delivery times: aluminium, lifts and electrical switchboards arrive months after the order, and they need a line of their own.
• No technical waiting times: curing, stripping formwork, plaster drying before paint, and watertightness tests.
• No approvals: inspections, laboratory tests and consultants' approvals take time, and some of them sit on the critical path.

How the construction schedule affects the price

Every month on site is a month of overheads: a works manager, a crane, security, containers and insurance. If site overheads are 60,000 shekels a month, a delay of two months costs 120,000 without any item changing. The full calculation is on the page site overheads, and ways to shorten the schedule are on the page construction cost saving.

A reliable schedule rests on a quantity takeoff: without quantities there is no duration for each activity. A quantity surveyor and a planner who work on the same file save each other double work.

Frequently asked questions

What is the difference between a Gantt chart and a schedule?

A construction schedule, in British usage the construction programme, is the plan: activities, durations and dependencies. The Gantt chart is a way to show it, as bars on a timeline.

Where do the norms come from?

From catalogues of standard times, from professional literature, and mainly from the contractor's experience on earlier projects. The quantities themselves come from the quantity takeoff.

How often is it updated?

Once a month is recommended, against the actual progress, to see early where a gap is opening.

Who builds a schedule like this?

The site engineer or the project manager, on the basis of quantities. A quantity surveyor for construction projects can supply the quantities and the norms as a basis.

More on this site

• Construction inputs and resources
• Site overheads
• Construction cost saving
• Quantity takeoff
• Quantity surveyor in Israel: Yaakov Avital, home page

* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.