Gantt chart
Gantt Chart
What is a Gantt chart?
- A bar chart of tasks over time
- Start with a WBS, and always show dependencies
- Without updates, the chart misleads
Once you introduce a Gantt chart, the questions asked in meetings change. Where people used to ask “When will it be done?”, they start asking “If this slips three days, what else slips with it?” Because each bar becomes someone’s commitment, even work that used to be waved through verbally as “sometime next week” is fixed as a start date and an end date. In other words, it is not a table that records the schedule but a tool that makes commitments visible. This is also why some resistance shows up early in adoption: the moment you draw a bar, an accountable owner is named.
In practice, a few distinctions are worth making. Most dependencies are “the next task starts only after the previous one finishes” (FS), but you can also use SS (start together), such as starting design once the first draft of the course materials is about half done, or add a waiting period (lag) in between. For the time scale, days are easier to read for projects under 3 months and weeks for projects over 6 months. One screen can hold at most 30–50 readable tasks. Beyond that, split the chart into a summary version for executives and detailed versions for each team. Also, a Gantt chart only presents the schedule. To calculate how many days of slack each task has, you need a separate network diagram.
The most common mistake is confusing bar length with effort. A “10-day bar” doesn’t mean the person spends ten full days on it, yet if you assign three such bars in overlap, the calendar looks fine while in reality one person gets buried. Progress works the same way: a self-reported 90% that is still 90% in the third week is a familiar sight everywhere. Unless you pin down the completion criteria by naming the deliverable, the progress column stays a comforting number. Redrawing the bars by pushing them back with every delay is also risky. Unless you keep the original baseline separately, the plan keeps chasing the actuals and you end up with a chart that says “we have never been late.”
John KimAuthor of B2B Marketing Design and CEO of Nanum Consulting
Soyeon KimExpert in design thinking, social venture startups, and the social economyHenry Gantt devised it in the 1910s to manage production schedules, and it spread through its use in managing large-scale operations during World War I.
Let’s walk through a hypothetical case. The talent development team at Company A, an auto parts manufacturer with 1,200 employees, decided to develop and launch a new team leader course in just 12 weeks. In the previous two cohorts, textbook printing ran late both times, and the start date slipped by 2 weeks each time. At the first meeting, the department head made it clear: “If it slips again, we can’t spend this year’s training budget.”
- The talent development manager carried the 38 work packages from the WBS straight onto the vertical axis and marked four milestones: instructor booking, materials finalization, textbook printing, and LMS registration.
- They set the durations in person with each owner, but the assistant manager handling printing said “7 days means business days, not 7 calendar days,” so the bar was extended to 10 days.
- We linked “finalize materials → print textbooks” as FS, and ran design in parallel as SS once the materials were 60% done, which pulled the overall schedule in by 2 weeks.
- Overlaying the bars by assignee showed that in the third week of May Assistant Manager Kim alone was carrying three tasks, so one case-development task went to an external writer.
- At the 30-minute update meeting every Friday, the team revised progress figures, and the team lead asked only one question each time: 'Does this week's slip affect the course start date?'
- In the end, they opened the course within 12 weeks without moving the start date. Printing delays, which had happened twice in three years, dropped to zero, and preparation took 2 weeks less than for the previous cohort.