Project Duration Calculator
Estimate four sequential stages, add a project buffer, and convert working days to weeks.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
This planner sums four stages in sequence and adds your chosen buffer. It does not schedule dates, parallel work, dependencies, or a critical path.
Worked example
calculated with the default values below
Stage 1 length 5 days · Stage 2 length 10 days · Stage 3 length 7 days · Stage 4 length 4 days · Project buffer 20 % · Working days per week 5 days With project buffer 31.2 days · Sequential duration 26 days · Calendar weeks 6.2 weeks · Longest single stage (not a dependency-based critical path) Stage 2 at 10 days · Note Stages are summed sequentially because task dependencies are not defined. The longest single stage is shown, not a dependency-based critical path.
Method and assumptions
D = (Σ tᵢ) × (1 + b ÷ 100) Stages are summed sequentially; the longest individual stage is not a dependency-based critical path. This planner sums four stages in sequence and adds your chosen buffer. It does not schedule dates, parallel work, dependencies, or a critical path. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Data sources
The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Disclaimer
These calculators give general date results. Public holidays, working-day conventions and time-zone rules are set locally and change, so confirm against the official calendar for anything legally or contractually binding.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
D = (Σ tᵢ) × (1 + b ÷ 100)
- t_i
- Stage durations (days)
- f
- Parallel factor
- p
- Parallel-mode flag (p = 1 when more than one person works in parallel, else 0)
- b
- Buffer (%)
- d
- Working days per week
- D
- Total scheduled days
- W
- Calendar weeks
Stages are summed sequentially; the longest individual stage is not a dependency-based critical path.
Frequently asked questions
Does the calculator model overlapping tasks?
No. It adds the four stage durations sequentially, then applies the buffer percentage. The longest individual stage is reported as a reference; without task dependencies, it is not a critical path.
Which inputs and limits apply to Project Duration Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. Stage 1 length: 0–500 days; Stage 2 length: 0–500 days; Stage 3 length: 0–500 days; Stage 4 length: 0–500 days; Project buffer: 0–100 %; Working days per week: 1–7 days D = (Σ tᵢ) × (1 + b ÷ 100) Stages are summed sequentially; the longest individual stage is not a dependency-based critical path. This planner sums four stages in sequence and adds your chosen buffer. It does not schedule dates, parallel work, dependencies, or a critical path. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
What is a complete worked example for Stage 1 length = 5 days; Stage 2 length = 10 days?
Inputs: Stage 1 length = 5 days; Stage 2 length = 10 days; Stage 3 length = 7 days; Stage 4 length = 4 days; Project buffer = 20 %; Working days per week = 5 days. Calculation: D = (Σ tᵢ) × (1 + b ÷ 100). Results: With project buffer = 31.2 days; Sequential duration = 26 days; Calendar weeks = 6.2 weeks; Longest single stage (not a dependency-based critical path) = Stage 2 at 10 days; Note = Stages are summed sequentially because task dependencies are not defined. The longest single stage is shown, not a dependency-based critical path..