What Is a Gantt Chart?

A Gantt chart is a bar chart of a project schedule. Each task gets its own row, time runs from left to right, and each task is drawn as a bar that starts on the day the task starts and ends on the day it finishes. One glance tells you what happens when, what overlaps, and when the whole project ends. This guide explains what a Gantt chart is, how to read one, its parts, where it came from, and when a different chart does the job better.

Gantt Chart Definition

Wikipedia’s article defines a Gantt chart as a type of bar chart that illustrates a project schedule: the tasks are listed on the vertical axis, time intervals run along the horizontal axis, and the width of each horizontal bar shows the duration of the activity. Microsoft’s Excel template gallery gives a shorter version: a diagram for visualizing a project schedule, using horizontal bars to track task duration and completion across a timeline.

How It Differs From an Ordinary Bar Chart

In an ordinary bar chart, every bar starts at zero and its length is a quantity, such as sales or votes. In a Gantt chart, bars start at different points. The position of the left end is a date, and the length is a stretch of time. That is why Excel and Google Sheets can only fake a Gantt chart with a stacked bar chart whose first segment, the start, is made invisible.

What a Gantt Chart Answers

• What happens when? Read down the left for tasks and across for dates.
• What runs at the same time? Bars that overlap horizontally run in parallel.
• What comes first? Bars further left start earlier.
• When does it all end? The right end of the last bar.
• How far along are we? If progress is shown, the shaded part of each bar.

The Parts of a Gantt Chart

Tasks

The rows. Each is one piece of work with a clear finish, such as “Design” or “Testing”. Microsoft’s template page notes that Gantt charts work best after the project has been broken down with a work breakdown structure or another planning method, which is where the task list comes from.

The Time Axis

The horizontal scale: days, weeks, months or quarters. Choose the unit that makes the shortest task visible. A two year program in days is unreadable; a two week sprint in months is a single column.

Bars

One per task. The left end is the start date and the right end is the finish date, so the length is the duration. Bars are often colored by phase, team or owner.

Milestones

Moments without duration, such as “Design approved” or “Launch”. They have no length, so they cannot be drawn as a bar; Gantt tools mark them with a symbol on the date instead.

Dependencies

Links between tasks. The most common one is “finish to start”: Build cannot start until Design is done. Modern Gantt charts, in Wikipedia’s words, also show these dependency relationships between activities, usually as arrows from the end of one bar to the start of the next.

Progress and the Today Line

Wikipedia describes a progress Gantt chart, where each task is shaded in proportion to its completion, so a task that is 60 percent complete is 60 percent shaded, starting from the left, with a vertical line at the current date. If everything is on schedule, every part of a bar to the left of the line is shaded.

The Critical Path

The longest chain of dependent tasks from start to finish. Any delay on it delays the whole project. Project software often highlights it in red; Wikipedia’s article shows an example made in Microsoft Project with the critical path in red. Microsoft’s own template page adds that PERT network diagrams are better for finding the critical path, while Gantt charts are better for tracking progress.

Gantt Chart Terms at a Glance

Wikipedia’s article notes that Gantt charts are usually first drawn with the early start approach, where every task starts as soon as its prerequisites are complete, and that this gives every task the most float. The Microsoft Project example in the same article draws the slack as thin lines after the non-critical tasks.

Gantt Chart Examples by Field

The chart looks the same in every field; what changes is the task list and the time scale. Microsoft’s Excel template gallery lists the people it has in mind, and each one uses the chart a little differently.

Project Managers

The classic use: every task of a project across a calendar, with owners and resources. Microsoft’s gallery also mentions assigning people, equipment and materials to tasks so you can see where the same resource is booked twice and move the schedule.

Construction

Phases such as site work, foundations, framing and finishes, each handed to a different subcontractor. The value of the chart is in the handovers: the moment one crew must be done so the next can start.

Events

Everything that has to happen before a fixed date: booking the venue, confirming vendors, sending invitations, printing. Events are the easiest case, because the end date cannot move, so the chart is read backward from it.

Software and Product Teams

Development milestones and feature releases, usually in weeks. Teams that plan in short cycles often keep a Gantt chart only for the release dates and the work that depends on other teams.

Consultants and Agencies

Client deliverables and review rounds. A simple chart shared with the client makes clear which dates depend on the client’s own feedback.

How to Read a Gantt Chart

1. Read the time axis first. Days, weeks or months? Where does the chart start?
2. Scan the rows from top to bottom. Tasks are usually listed in the order they begin.
3. Find the parallel work. Look for bars that overlap in time. In the chart above, Design and Content overlap for four days, and Content and Build overlap too.
4. Follow the arrows, if there are any. They tell you which delay will push which task.
5. Find today. Everything left of today should be done. Anything unshaded to the left of the line is late.

A Short History of the Gantt Chart

Karol Adamiecki and the Harmonogram, 1896

According to Wikipedia’s history of the chart, the first known tool of this type was developed in 1896 by Karol Adamiecki, a Polish engineer who ran a steel rolling mill and called his chart a harmonogram. He published it only in Polish and Russian, which limited its adoption and the recognition of his authorship.

Henry Gantt, 1910 to 1915

The chart is named after Henry Laurence Gantt (1861 to 1919), an American mechanical engineer and management consultant in the scientific management movement, who designed his chart around 1910 to 1915. Wikipedia notes that Hermann Schürch published similar charts in 1912 while discussing a construction project, and that charts of that type seem to have been in common use in Germany at the time. One of the first major uses of Gantt charts was by the United States during World War I, at the instigation of General William Crozier, and Gantt charts were later used on projects such as the Hoover Dam and the Interstate highway system.

From Paper to Software

The first Gantt charts were drawn on paper and had to be redrawn whenever the schedule changed. Personal computers in the 1980s made complex Gantt charts common, and web-based tools followed. A 1999 book on project scheduling, cited in the Wikipedia article, called Gantt charts one of the most widely used management tools for project scheduling and control.

Gantt Chart vs Timeline

People often use the two words for the same thing, but they answer different questions. A timeline, in Wikipedia’s definition, is a list of events in chronological order, typically drawn along a bar labeled with dates. Its events are points. A Gantt chart’s tasks are stretches of time.

The timeline tells a stakeholder the dates that matter. The Gantt chart tells the team how long each piece takes and what overlaps. Our timeline maker spaces events evenly by order, which suits milestones and history; the timeline templates are a quick start. For durations and overlaps, use a Gantt chart.

When a Gantt Chart Works, and When It Does Not

Where It Shines

• Projects with a fixed end date and clear tasks, such as events, launches, construction phases and research projects.
• Plans shared with people outside the team. Wikipedia notes that Gantt charts are often preferred over network diagrams because they can be read without training.
• Tracking progress against the plan, with a today line and percent done.

Where It Struggles

• Many dependencies. Linked Gantt charts, Wikipedia warns, quickly become cluttered in all but the simplest cases. A network diagram shows the relationships more clearly.
• Uncertain work. The same article summarizes a critique that the chart flattens assumptions, which can make it harder to respond to uncertainty and change. Work that is discovered as you go fits a task board better.
• Constant change. A Gantt chart drawn by hand goes stale the day a task slips. If dates change weekly, build it from data so it can be redrawn.

How to Make a Gantt Chart

You need a list of tasks, each with a start date and either an end date or a duration. From there, three routes:

• In a spreadsheet: a stacked bar chart with the start series hidden. Our guides cover Excel and Google Sheets step by step.
• In project software: Gantt charts are generated from the task list, with dependencies and the critical path calculated for you.
• In a browser: paste the task list into our Gantt chart maker. It takes dates or numbers of days, the task each one waits for and percent done, and exports PNG or SVG.

Open the example plan in the Gantt chart maker

The charts on this page were drawn with the spreadsheet trick in our bar graph maker, so you can open any of them and see how the invisible start series works.