Project Scheduling and Gantt Charts

A project schedule tells everyone what happens when: which activities, in what order, how long each takes and when the project finishes. A Gantt chart is the most common way to show it: one row per activity and a horizontal bar across a calendar. In this lesson you'll build the schedule for the launch tasks of Rosa's bakery in Austin, from the activity list to a finished Gantt chart in Excel, including a federal holiday that quietly pushes a date.

1. List activities
2. Sequence them
3. Estimate durations
4. Build the Gantt chart
5. Set the baseline

Step 1: from work packages to activities

In the previous lessons the WBS gave you deliverables (nouns). Now you list the activities (verbs) needed to produce each one. "Online menu" becomes "configure menu and prices"; "product images" becomes "photograph 40 products." Keep each activity small enough to have a clear owner and a clear finish: if you can't tell whether it's done, it's too vague.

Rosa's PM listed six activities for the launch stretch of the project, plus the go-live milestone. Planning and closing are scheduled separately, so this lesson focuses on these core launch tasks.

Step 2: sequence the activities

Some activities can't start until others finish; others can run in parallel. A dependency describes that link. There are four types:

You can add a lag (a forced wait, like "paint must dry 2 days before the next coat") or a lead (overlap, like "start testing 3 days before development finishes"). Use both sparingly and write down why they exist.

Step 3: estimate durations

First, don't confuse effort with duration. Effort is the number of work hours. Duration is the number of workdays on the calendar, and it depends on how much time people can actually give. Configuring Rosa's menu takes about 24 hours of effort, but her manager can spend only 4 hours a day on it while running the shop, so the duration is 24 ÷ 4 = 6 workdays.

When an activity is uncertain, ask for three numbers instead of one and combine them with the PERT (beta) formula, which gives extra weight to the most likely case:

PERT estimate  = (Optimistic + 4 × Most likely + Pessimistic) ÷ 6
Std. deviation = (Pessimistic − Optimistic) ÷ 6

Product photography: O = 3, M = 4, P = 11 days
PERT = (3 + 16 + 11) ÷ 6 = 30 ÷ 6 = 5 days
SD   = (11 − 3) ÷ 6 ≈ 1.3 days

The photographer's "about 4 days" ignores what could go wrong (a reshoot, a sick day, croissants that don't look right under the lights). The PERT estimate of 5 days builds some of that in, and the standard deviation tells you how uncertain the estimate is.

Step 4: build the schedule and the Gantt chart

With the activities, links and durations, you calculate each date. The schedule starts Monday, January 4, 2027. Every duration below counts workdays (Monday to Friday) and skips Martin Luther King Jr. Day on Monday, January 18:

Look at activity B: 6 workdays take 9 calendar days, because they span a weekend and the holiday. Forgetting holidays is one of the easiest ways to promise a date you can't hit.

The Excel formulas behind it

Put the holiday dates in a range named Holidays. With the start in column D and the duration in column E:

Finish date:            =WORKDAY(D2, E2-1, Holidays)
Check workdays:         =NETWORKDAYS(D2, F2, Holidays)
Start of a successor:   =WORKDAY(F2, 1, Holidays)
Start after several:    =WORKDAY(MAX(F4, F5, F6), 1, Holidays)
Calendar days:          =F2-D2+1

For the bars, put one date per column across row 1 (starting in column H) and apply conditional formatting to the grid with this formula, which colors a cell when its date falls between the task's start and finish:

=AND(H$1>=$D2, H$1<=$F2)

Step 5: milestones and the baseline

A milestone is a significant point in time with zero duration: "go-live," "permit approved," "contract signed." Milestones make a schedule easy to read for busy stakeholders: the sponsor may never look at activity C, but she'll ask about go-live every week.

Once the sponsor approves the schedule, save a copy of the dates as the baseline. From then on, you compare actual dates to the baseline instead of quietly editing the plan. In Excel, that's simply two extra columns, "Baseline start" and "Baseline finish," pasted as values and never changed without an approved change request.

Common scheduling mistakes

Task 1: (2 + 12 + 10) ÷ 6 = 24 ÷ 6 = 4 days
Task 2: (4 + 24 + 8) ÷ 6  = 36 ÷ 6 = 6 days
Task 3: (6 + 36 + 18) ÷ 6 = 60 ÷ 6 = 10 days
Total: 20 workdays

Summary

• Break work packages into activities (verbs) with clear owners and clear finishes.
• Link activities with dependencies; finish-to-start is the default. Document any lags and leads.
• Effort is hours of work; duration is workdays on the calendar. PERT = (O + 4M + P) ÷ 6.
• In Excel, finish = WORKDAY(start, duration − 1, Holidays); color the Gantt bars with conditional formatting.
• Milestones have zero duration. Save a baseline once the schedule is approved.

Next lesson: The Critical Path Method (CPM) and Float. You'll find the chain of activities that controls the finish date and calculate exactly how much each other task can slip.