Project Phase and Timeline Estimator
List the tasks, how many working days each takes and what each must wait for. The estimator finds the earliest finish in working days and the chain of tasks that sets it — the critical path. Approvals and long-lead deliveries go in as tasks with allowances you choose, not dates anyone has promised.
What this tool estimates
The earliest finish of your task network in working days, the critical path that sets it and each task's float — and, only if you give a start date and working week, the calendar dates.
What it cannot decide
- How long any task, approval or delivery will really take — every duration is your assumption.
- When an authority (fire service, Electrical Inspector, DISCOM, pollution control board) will decide. No approval date is predicted or promised.
- Crew or equipment limits: tasks that share one crew are assumed able to run together unless you link them.
- Overlaps such as start-to-start links or lags — every link here is finish-to-start.
- A guaranteed completion date. The finish is arithmetic on your inputs, not a commitment.
Result
More than one chain of tasks sets the finish: . A slip on any of them delays the finish.
Approval and procurement allowances sit on the critical path. They are your planning assumptions — no authority or supplier has committed to them — and every day they run over moves the finish by a day.
| Task | Days | Working days | Float | Dates |
|---|
| Task | Overrun | New finish | Finish moves by |
|---|
Every duration is your assumption. The finish is arithmetic on your inputs, not a guaranteed completion date.
Method version 6 October 2026. A screening estimate, not a design: see the limits below.
Approval and procurement allowances: what to enter
On many MEP jobs the finish is set less by installation crews than by things nobody on site controls: authority approvals and inspections, the power connection and long-lead equipment. Enter each as its own task, with the allowance you are prepared to plan on, and link the work that cannot start without it. The estimator treats every allowance as your assumption. It does not know how long an authority or a supplier will take, and it does not predict a decision.
- Fire: approvals and inspections by the state fire authority, where the project needs them — see the fire NOC guide for factories.
- Electrical: the Electrical Inspector's (CEIG) clearance before an HT installation, substation or DG set is energised — see the CEIG approval guide.
- Power connection: the DISCOM's sanction and any connection or line work — see why HT connections run late.
- Solar: the DISCOM's net-metering sanction and feasibility, where a plant is in scope — the capital side is in the 1 MW solar plant cost breakdown and the commercial solar calculator.
- Pollution control board: consent to establish and consent to operate, where the activity needs them — see the CTE and CTO guide.
- The whole sequence: the factory approvals roadmap, and the Government of India's National Single Window System (nsws.gov.in) to find which central and state approvals apply.
Which approvals apply, and in what order, depends on the state, the occupancy and the connected load. Confirm each with the issuing authority before you fix the programme, and replace each allowance with the authority's decision when you have it.
How this calculator works — and where it stops
What it calculates
The earliest finish of a task network in working days, the critical path that sets it and each task's float — and, only when a start date and working week are given, the calendar dates of each task and of the finish.
Inputs
- Tasks, each with a short ID, an optional description and a type: work, approval allowance or procurement allowance.
- The duration of each task in whole working days (0 for a milestone).
- Predecessors: the IDs of the tasks each one must wait for. Every link is finish-to-start.
- Optional working calendar: a start date, the days of the week the site works and any holiday dates.
Method
- Order the tasks so that each comes after its predecessors. A loop (A after B after A) has no such order, so it is refused and the loop is named; unknown predecessors, duplicate IDs and negative durations are refused too.
- Forward pass: earliest start = the latest earliest finish among the task's predecessors (0 when it has none); earliest finish = earliest start + duration.
- Earliest project finish = the latest earliest finish of any task.
- Backward pass: latest finish = the earliest latest start among the task's successors (the project finish when it has none); latest start = latest finish − duration.
- Float = latest start − earliest start. Tasks with no float are critical; the critical path is the chain of critical tasks in which each starts as its predecessor finishes. Every such chain is listed, up to five.
- Calendar, only with a start date and ticked working days: working day 1 is the first working date on or after the start date, and each later working day skips the non-working weekdays and the holidays entered. A task occupies working days ES + 1 to EF.
- Sensitivity: each task in turn takes 20% longer, rounded up to whole days, and the finish is recomputed; then every task at once.
Assumptions
- Every link is finish-to-start with no lag or overlap; work that overlaps has to be split into separate tasks.
- Crews and equipment are unlimited: two tasks that need the same crew can run together unless you link them.
- Every duration — approval and procurement allowances included — is the user's assumption. The tool contains no durations, approval times or lead times of its own.
- One working week applies to every task; a crew on a different week (a seven-day testing team, say) is not modelled.
Limitations
- Does not predict or promise when an authority (fire service, Electrical Inspector, DISCOM, pollution control board) will decide. An approval allowance is a planning figure the user sets.
- Gives no guaranteed completion date: a finish date is arithmetic on the inputs.
- No resource levelling, cost loading, weather or productivity model.
- The critical path is found on the network as entered — a missing link can hide the real one.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- Task A: 5 working days, no predecessors
- Task B: 10 working days, after A
- Task C: 7 working days, after A
- Task D: 3 working days, after B and C
- Example calendar: start Monday 2 Nov 2026, Monday to Saturday working, one example holiday on 17 Nov 2026
Working
- Forward pass: A runs from day 0 to day 5; B and C both start at day 5; B finishes at day 15 and C at day 12.
- D waits for the later of B (15) and C (12), so it runs from day 15 to day 18.
- Earliest finish = 18 working days.
- Backward pass: D must start by day 15, so B must finish by 15 (no float) and so must C — C can start as late as day 8, which gives it 3 working days of float.
- Critical path: A → B → D (5 + 10 + 3 = 18 working days).
- Calendar: working day 1 is Mon 2 Nov 2026; Sundays and the 17 Nov holiday are skipped, so working day 18 is Mon 23 Nov 2026, 22 calendar days after the start counting both ends.
Result. 18 working days, critical path A → B → D, with 3 working days of float on C. On the example calendar the arithmetic finish is Mon 23 Nov 2026 — a date from the inputs, not a commitment.
Sensitivity — what moves the answer
- A critical task moves the finish day for day: B taking 12 working days instead of 10 moves the finish from 18 to 20.
- A task with float absorbs a slip up to its float: C taking 9 days instead of 7 leaves the finish at 18; at 11 days it moves to 19.
- If every task overran by 20% (each rounded up to whole days), the example would take 22 working days, not 18.
- On a calendar, every holiday or lost working day inside the programme moves every later date by a working day.
How engineers use the result
To agree the logic of a programme before arguing about durations: which approvals and deliveries the finish really depends on, where float exists to absorb a slip, and which allowances need an early application or an early order.
When a professional design must replace it
Before committing to a completion date in a contract, a lease or a production plan: the durations need the contractor's resourced programme, supplier lead-time quotations and the current status of each application — and an approval allowance stays an assumption until the authority decides.
Sources
- Critical path method — forward and backward pass with total float — standard scheduling arithmetic; no code clause is applied
- National Single Window System (Government of India) — to identify which central and state approvals a project needs; verify each requirement with the issuing authority
Questions people ask before using it
What do I need before building a timeline with this estimator?
A task list for the job — design, approvals, long-lead orders, installation, testing and handover, at the level of detail you can defend — with a duration in working days for each and the tasks each one must wait for. For dates, add the planned start date, the days your site works each week and any holidays. Durations from the contractor's programme, supplier lead-time quotations and your own record with the authorities beat guesses: the estimator has no durations of its own.
Which site conditions could change the timeline?
Anything that lengthens a task on the critical path or adds a link: a late civil handover of plant rooms and shafts, queries on an approval or inspection, a DISCOM connection that needs line work, long-lead equipment (transformers, panels, chillers, DG sets) arriving late, shutdown windows in an operating plant, monsoon or heat restrictions, and crews shared between areas. A task with float absorbs a slip up to its float; a critical task moves the finish day for day.
What should I send an engineer to review my timeline?
The task list from this page (download the CSV or JSON), the project layout and equipment schedule, the civil programme with the dates each area is handed over, supplier lead-time quotations for the long-lead items, and the approvals you expect to need with where each application stands. An engineer can then check the links and durations against the scope and the bill of quantities.
Optional: ask an engineer to look at it
The result above is yours with no form. If you want an engineer to check it against your drawings, schedules or bills, send a request. Nothing is sent until you press the button.
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