Gantt Chart Maker

How the chart calculates task positions

A Gantt chart combines a task table with a horizontal time scale. This maker treats every accepted date as midnight UTC, which prevents daylight-saving changes from making one calendar day look shorter or longer than another. It finds the earliest task start and latest task end, then calculates each bar from three values:

start offset = (task start − project start) ÷ 86,400,000 milliseconds

bar width = inclusive task days ÷ inclusive project days × plot width

The end date is inclusive. A task that starts and ends on the same date therefore occupies one day rather than disappearing as a zero-width bar. The darker progress overlay uses bar width × progress ÷ 100, with progress constrained to 0 through 100.

Worked example

Suppose the project runs from January 1 through January 20, giving 20 inclusive calendar days and an 894-pixel plot. A Research task from January 1 through January 3 has an offset of 0 and a bar width of 3 ÷ 20 × 894 = 134.1 pixels. A Design task from January 5 through January 8 starts 4 ÷ 20 × 894 = 178.8 pixels into the plot; at 50% progress, its darker overlay is 89.4 pixels wide. A one-day Launch task on January 20 starts at 19 ÷ 20 × 894 = 849.3 pixels. If Design depends on Research, it must start on January 4 or later because the predecessor’s end date is included.

What the dependency check means

Each task can have one finish-to-start predecessor. In this common relationship, the successor should start after the predecessor’s inclusive end date. The editor draws a connector from the predecessor bar to the successor bar and reports a conflict when the successor starts on or before that date. It also detects self-links, missing predecessors, and dependency cycles such as A depending on B while B depends on A. These issues block export until they are corrected, but the chart remains visible to help diagnose the schedule.

Reading and sharing the result

Bar spacing is based on calendar days, not working days. Weekends and public holidays remain part of the scale. SVG preserves the vector chart for documents and presentations, CSV preserves the underlying task table, and Print lets the browser create paper output or a PDF. CSV cells that could be interpreted as spreadsheet formulas are prefixed as text before download.

This is a manual planning aid. It does not calculate a critical path, allocate resources, apply working calendars, support lead or lag, or automatically move successor dates. For those needs, use dedicated project scheduling software. Here, the dates you enter remain authoritative, and dependency warnings identify where manual correction is needed.