Gantt chart: a practical guide with a complete example

The Gantt chart is the most widely used way to represent a project over time: each task is a bar on a calendar, as long as its duration and positioned between its start and finish dates. It is easy to read, but a well-built Gantt chart is more than a drawing: it is a model that calculates dates from durations, dependencies and calendars, and shows which tasks cannot afford a delay.

This guide explains the elements of a Gantt chart, presents a complete example and describes the steps for building a reliable one.

What is a Gantt chart#

The chart is named after Henry Gantt, who popularized it in the early twentieth century for production planning. The principle has not changed: time runs along the horizontal axis and tasks along the vertical axis. Each bar shows when a task starts, how long it lasts and when it ends.

Today the Gantt chart is the reference tool for construction sites, product launches, events, software implementations and research projects: any context with interdependent tasks and a deadline to meet.

The elements of a Gantt chart#

• Tasks: the work to be done, with a duration expressed in working days.
• Summary tasks: they group other tasks into phases; their duration derives from the tasks they contain.
• Milestones: zero-duration events, such as a delivery or an approval.
• Dependencies: the links that determine the order in which work is carried out.
• Lead and lag: an interval added to a dependency, for example three days of drying time.
• Constraints and deadlines: dates that a task cannot or should not exceed.
• Calendars: working days, holidays and exceptions, at project level or for individual people.
• Critical path and float: the tasks that determine the finish date, and how much the other tasks can slip.
• Baseline: a copy of the approved plan, to be compared with actual progress.

The four dependency types

Finish-to-start is by far the most common dependency; the other types are used to represent overlapping tasks.

An example: renovating an apartment#

The calculation is expressed in working days. Demolition occupies days 1–5. Electrical work runs from day 6 to day 13. Plumbing starts two days after the electrical work, on day 8, and finishes on day 12: it therefore has one day of float. The screed waits for both to be completed and runs from day 14 to day 17. After three days of drying, flooring runs from day 21 to day 26, painting from day 27 to day 30, and the handover falls at the end of day 30.

The critical path is therefore: demolition, electrical work, screed, flooring, painting, handover. A two-day delay by the electrician moves the handover by two days. A one-day delay in plumbing, on the other hand, has no effect: it is absorbed by the day of float.

This is the value of a Gantt chart with dependencies: calculations do not have to be redone by hand, and it is immediately clear where to focus attention.

How to build a Gantt chart in seven steps#

1. Break down the work into phases and tasks (the work breakdown structure, or WBS), down to a level where each task has an owner and an estimable duration.
2. Estimate durations in working days, not dates.
3. Link the tasks with the appropriate dependencies, adding lead or lag where needed.
4. Set up the calendars: holidays, closures and people’s working days.
5. Add constraints and deadlines only where they are actually required, for example a contractual date.
6. Assign people and check that no one is overallocated in the same weeks.
7. Save a baseline once the plan is approved, and update progress regularly.

The most common mistakes#

• Entering dates by hand instead of having them calculated from dependencies: at the first delay, the plan is no longer reliable.
• Too many constraints: they block the calculation and hide real problems.
• Tasks that are too large: a three-month bar says nothing useful about the status of the work.
• Neglecting calendars: holidays and closures affect dates more than one might expect.
• Not saving a baseline: without a reference, it is impossible to quantify a delay.

Gantt chart, board or list: when to use each#

The Gantt chart is indispensable when timing and dependencies are decisive. A kanban board is ideal for following day-to-day work by status (to do, in progress, done). A list is the fastest way to enter and review many tasks. The best approach is to use all three views together, on the same plan.

How to do it with Gantify#

Gantify is built around these rules. Tasks can be created directly or pasted from Excel, indented with Tab to form phases and linked with FS, SS, FF and SF dependencies, with lead and lag; once calendars and constraints are set, the engine calculates the dates and the critical path. You can save a baseline, see the variance of each task, switch to the Board, List, Calendar and Workload views and share the plan through a read-only public link. An existing Microsoft Project plan can be opened directly from its .mpp file.

To get started faster, the AI assistant can propose a first version of the plan, with phases, tasks and dependencies, from a description of the project.

Frequently asked questions#