Planning & Budgeting
Build Project Timeline Calculator
Estimates project duration from trade sequence and working days
Updated 4 June 2026 · Live
What this tool does
Estimates project duration from trade sequence and working days.
Formula Used
People also use
How the build project timeline calculator works
Estimates a project's duration in working days from the number of tasks, the average days per task, how much the tasks overlap, your crew size, and a weather buffer. The calculator runs a standard sequencing heuristic — tasks in series, reduced for overlap and crew size, then padded for weather — and returns a duration with a working-weeks breakdown. Every figure is an estimate — site conditions always move the final number.
Overlap and sequencing
Few trades work in strict sequence. Overlapping follow-on tasks — second fix starting before first fix has finished everywhere — is where most programme time is saved, but too much overlap causes trades to clash. The overlap default of 25% is a sensible starting point; it can rise on well-coordinated jobs and fall on tight or single-access sites.
What this tool does not do
It does not replace a professional programme, factor regional labour availability, account for long-lead materials, or confirm Building Regulations sign-off timings. Those remain the responsibility of your contractor, project manager, or building control officer.
On-site considerations for a build programme
The critical path — the longest chain of dependent tasks — sets the real finish date, not the busiest week. Adding crew to a task that is off the critical path does not shorten the programme, which is why the crew-size effect here follows a diminishing-returns curve rather than a straight division.
Building Regulations and compliance
Domestic projects over £100,000 that involve more than one contractor are notifiable under CDM 2015. The client (you) has legal duties even on a domestic project, including allowing adequate time in the programme for the work to be carried out safely. When in doubt, a pre-application enquiry to the local authority can give early clarity, which tends to be less costly than retrospective correction.
Before you commit to a programme
A programme built from rough task durations is a planning aid, not a contract. The sequence and float are worth confirming with whoever is running the job, and time should be allowed for inspections, deliveries, and the drying or curing that sits between trades. Cross-checking this estimate against a contractor's programme highlights where your assumptions on overlap or crew differ from theirs.
Adjusting the defaults
Every input in this calculator is editable. Enter your own task count, average task duration, overlap, crew size, and weather buffer — the output recalculates instantly. If the defaults feel off for your project type, your own numbers always override them.
Using this build project timeline calculator alongside other BuildMetricLab tools
This calculator works best as part of a planning workflow. Pair this programme with our project budget, labour-cost, and material-cost calculators to build a complete picture before you commit. All BuildMetricLab tools run entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the maths.
Sources & methodology
Estimates a project's duration using an in-house planning heuristic: serial task time (tasks × average days) is reduced for overlap and for crew size — dividing by the square root of crew, reflecting diminishing returns — then padded by a weather buffer, as D = n·d·(1−o)/√c·(1+b). It is an illustrative estimate, not a substitute for a critical-path programme. Every result is calculated from the values you enter, and all inputs are editable.
Frequently asked questions
Are build project timeline calculator results accurate enough to set a programme?
Use them as a starting estimate only. Confirm the sequence and durations with your contractor or project manager before committing — trade availability, weather, inspections and deliveries all move the real finish date.
How does task overlap change the result?
Overlap is the share of follow-on work that runs in parallel with earlier tasks rather than waiting for them to finish. Higher overlap shortens the programme but needs good coordination; the default of 25% suits a typical well-run job. The calculator caps overlap below 100%, because tasks can never fully collapse into a single day.
Does this replace professional advice?
No. This tool is a planning estimator. For works that affect structure, Building Regulations, Party Wall, gas, electrics, drainage to a sewer, or similar, consult a suitably qualified professional.
Why does a bigger crew not cut the time proportionally?
Doubling the crew rarely halves the duration — access, supervision and task dependencies get in the way. The calculator models this with a diminishing-returns curve, dividing by the square root of crew size, so each extra person helps a little less than the last.
Related tools
Calculators from other categories that planners often reach for next.