Construction Schedule Duration Calculator

Workload mode estimates required working days from measurable work and crew productivity:

• Output per day = Crew Size × Productivity Rate × Hours per Day × (Efficiency ÷ 100)
• Raw workdays = Quantity ÷ Output per Day
• Planned working days = ceil(Raw workdays) (or standard rounding)

Date mode evaluates an existing schedule window:

• Calendar days = (End − Start) + 1 (inclusive)
• Baseline working days = calendar days excluding selected non-working weekdays
• Planned working days = max(0, Baseline working days − Holiday days)

Finish dates are simulated day-by-day to respect weekends and extra non-working days.

1. Select From workload to forecast duration from quantities and crew productivity.
2. Enter the start date and choose which weekdays are non-working.
3. Fill workload inputs (quantity, crew size, rate, hours, efficiency), then calculate.
4. Add holiday and delay days to model real project constraints.
5. Use From dates to analyze a known start–end period and compare baseline versus adjusted duration.
6. Download results using the CSV or PDF buttons for documentation.

1) Why duration accuracy matters

Construction schedules drive labor cost, equipment utilization, subcontractor sequencing, and material lead times. A small duration error can ripple into overtime, idle crews, and rework. This calculator helps you quantify time impacts before committing to a baseline plan or recovery strategy.

2) Two planning lenses: dates and workload

Date mode evaluates a fixed window by separating calendar days from working days. Workload mode forecasts finish dates from measurable quantities and productivity. Using both lenses is common: validate a contractual milestone with date mode, then stress‑test production assumptions with workload mode.

3) Productivity inputs and realistic ranges

Field productivity varies by scope, access, and learning curve. A practical way to estimate is “units per person‑hour” and then scale by crew size and net work hours. Many site activities deliver only 6–8 net hours inside a 10‑hour shift after briefings, staging, and handoffs.

4) Efficiency is not a guess; it is a control

The efficiency factor captures congestion, micro‑stoppages, and rework. Typical planning bands are 70–90% for steady work and 55–75% for complex interfaces. Use a lower value when trades overlap heavily or when access is restricted, then update as actuals stabilize.

5) Weekends, holidays, and rule clarity

Schedule disputes often come from inconsistent calendar rules. Define non‑working weekdays early, then treat holidays as additional non‑working days. This calculator simulates day‑by‑day, so the finish date respects weekends automatically, instead of assuming every day is available.

6) Delay days and risk buffers

Weather, permits, inspections, and procurement are common delay drivers. Add delay days to represent known constraints or conservative buffers. For higher‑risk scopes, planners often carry a 5–15% time contingency, then consume it only when a risk event is verified.

7) What to report to stakeholders

When presenting results, show both planned working days and elapsed calendar days. Decision makers usually care about the finish date, while supervisors care about production targets per day. Exporting to CSV or PDF makes it easier to attach results to daily reports and look‑ahead meetings.

8) Improving accuracy with feedback loops

Update inputs weekly using actual installed quantities and observed crew hours. If output per day is below plan, adjust the productivity rate or efficiency factor, then rerun the forecast. Continuous recalculation supports early corrective actions, such as resequencing work or increasing crew size.

1) Which mode should I choose?

Use workload mode to forecast a finish date from quantities and production. Use date mode to analyze a known start–end window and confirm working days versus calendar days.

2) What does “productivity rate per person-hour” mean?

It is the amount of work one person completes in one productive hour, such as 0.35 m³/hr. The calculator multiplies it by crew size, hours per day, and efficiency.

3) How should I set the efficiency factor?

Start with 85% for steady, repeatable tasks. Reduce it for congestion, restricted access, or frequent handoffs. Increase only when site conditions and measured outputs consistently support it.

4) How are holidays and delays applied?

They are treated as extra non-working days that would otherwise be workable. The finish date is simulated day-by-day so these days push completion forward realistically.

5) Why do I see different “working days” and “elapsed calendar days”?

Working days exclude selected non-working weekdays and added non-working days. Elapsed calendar days include every date from start to finish, which is what clients often track.

6) Can I model a six-day workweek?

Yes. Uncheck Saturday as a non-working weekday, keep Sunday non-working, and rerun. The simulator will count Saturdays as workable and shift the finish date earlier.

7) What is a good practice after exporting results?

Attach the PDF to look-ahead meeting notes, and log the CSV values in your tracking sheet. Re-run weekly with actual installed quantities to keep forecasts current.