Project Timeline Calculator

Project duration in days = Total labor hours / (Crew size x Hours per day x Productivity factor). For example, 2,000 labor hours with a 4-person crew working 8-hour days at 85% productivity: 2,000 / (4 x 8 x 0.85) = 73.5 working days. Convert to calendar weeks and add time for inspections, material deliveries, weather delays (typically 10-15% of working days for outdoor work), and other contingencies.

The productivity factor (also called crew efficiency) accounts for non-productive time during the workday: breaks, tool setup, material handling, minor delays, and transition between tasks. A factor of 0.85 (85%) is commonly used for interior trades; 0.75-0.80 is typical for outdoor crews subject to weather and site conditions. The productivity factor reduces effective output below the theoretical crew hours available.

Critical Path Method (CPM) scheduling identifies the longest sequence of dependent tasks (the critical path) that determines the minimum project duration. Activities on the critical path have zero float (no scheduling flexibility); any delay directly delays project completion. Non-critical activities have float and can be delayed without affecting the end date. CPM scheduling is required on most commercial construction projects and public contracts.

Weather delays depend on project location, season, and work type. The U.S. Army Corps of Engineers uses historical weather data to calculate anticipated weather working days for scheduling government contracts. Interior work is rarely delayed by weather. Outdoor concrete, masonry, painting, and roofing work can be delayed 20-40 working days per year in cold or wet climates. Most project schedules include a weather contingency of 5-15% of total duration.

A Gantt chart is a bar chart showing task durations over calendar time. It is easy to read but does not explicitly show task dependencies or float. A CPM schedule (often displayed as a network diagram or activity-on-arrow diagram) explicitly shows task dependencies, critical path, and float. CPM schedules are produced by scheduling software (Primavera P6, MS Project) and are required for complex construction projects. The bar chart view of a CPM schedule is effectively a Gantt chart.