Gantt charts

A Gantt chart, or bar chart, is the most familiar way to show a schedule. Each activity is a horizontal bar on a time scale, starting at its planned start date and ending at its planned finish. It is easy to read, which is why it is used in site offices, progress meetings and reports to clients and owners. Henry Gantt popularised it a century ago, and it remains the standard output of every scheduling program.

A plain bar chart shows when work is planned but not why. It does not show logical dependencies, so it is hard to see the effect of a delay to one activity on others. Modern scheduling tools therefore draw linked Gantt charts, in which dependency arrows connect bars and the critical path is highlighted, combining the readability of bars with the logic of a network. Bars can show baseline and actual dates side by side, percent complete, float, milestones (shown as diamonds) and summary bars for WBS groups.

Good practice keeps charts at the right level of detail for the audience: a one-page summary with major milestones for senior management, a level-3 programme for the project team and three-week look-ahead charts for supervisors. Progress is marked with a data date line; bars that fall to its left without being complete are behind schedule. Resource histograms below the bars show manpower or equipment needs over time, which helps spot unrealistic peaks.