What Is a Cash Flow Forecast in Construction?
A cash flow forecast is a projection of when money will move in and out of a project over its timeline — when materials and subcontractors need paying, and when progress claims will bring money back in. Construction cash flow is almost never a straight line: spend typically starts slow, ramps up through the middle of the job, then tapers off toward completion, producing the S-shaped curve builders call the S-curve. Forecasting it matters because a profitable job can still run out of cash if money goes out faster than it comes in, and that gap — not lack of profit — is what sinks builders.
Key takeaways
- A cash flow forecast projects when money will be spent and received across a project’s timeline, not just how much profit the job will make overall.
- Construction spend typically follows an S-curve — slow start, steep middle, tapering finish — rather than a straight line, so forecasts need to reflect that shape.
- Forecasts are used to time progress claims, plan when subcontractors and suppliers need paying, and manage the working capital gap between the two.
- A job can be profitable on paper and still fail if cash goes out faster than it comes in — the forecast is what exposes that risk before it happens.
What is a cash flow forecast?
A cash flow forecast maps out, period by period, how much money a project is expected to pay out and receive, so a builder sees the running cash position rather than just the final profit figure. It is built from the priced Bill of Quantities and the program: costs are spread across the weeks they will actually be incurred, and progress claims are mapped against the dates they will be paid.
The output is usually a graph plotting cumulative spend against cumulative receipts — the gap between the two lines at any point is the working capital the builder needs to fund until the next claim lands.
Why construction cash flow forms an S-curve
Spend on a typical job is not spread evenly — it starts slowly during mobilisation, accelerates through the bulk of construction, then tapers as finishing trades wrap up. Plotted cumulatively, that pattern produces an S-shaped curve rather than a straight diagonal line.
Because most contracts price on this same curve — small early claims, the largest claims mid-project, a modest final claim — the S-curve is a benchmark for sense-checking whether actual progress and cash flow are tracking where they should be.
| Project phase | Typical share of spend | Cash flow pattern |
|---|---|---|
| Mobilisation / early works | 5–10% | Slow ramp-up, minimal claims paid yet |
| Main construction | 65–75% | Steepest spend and claims, biggest working capital need |
| Finishing trades | 15–20% | Spend tapering, claims catching up |
| Practical completion / close-out | 5% | Final claim, retention release, minimal new spend |
Using a cash flow forecast to manage working capital
The practical value of a forecast is spotting the gap between paying subcontractors and receiving payment from the client before it becomes a problem, not after. A builder who knows a month will run cash-negative can arrange finance, negotiate supplier terms, or time a claim to close the gap — none of which is possible if the shortfall is only discovered once the account runs low.
- Time progress claims to align with actual cash outlay, not just contract milestones
- Flag months where committed payments to subs and suppliers exceed expected receipts
- Compare forecast against actual spend regularly, adjusting as the program shifts
- Use the forecast to negotiate payment terms or finance before a shortfall hits
Building a cash flow forecast with My Trade Hub
A cash flow forecast is only as reliable as the cost data behind it, and that starts with a properly priced Bill of Quantities rather than a rough guess. My Trade Hub’s automated quantity takeoff and editable rates library produce that priced BOQ directly from your plans, giving you real cost figures — by trade, by item — to spread across the project program instead of working from a single lump-sum total.
From there, invoicing and progress claims stay linked to the same underlying job data, so the forecast built at tender stage can be checked against what is actually being claimed and paid as the job proceeds.
Frequently asked questions
What is an S-curve in construction?
An S-curve is the S-shaped line produced when cumulative project spend or progress is plotted over time — slow at the start, steep through the middle, tapering toward completion. It benchmarks whether actual cash flow is tracking where it should be.
Why do I need a cash flow forecast if the job is already profitable?
Profit is calculated over the whole job, but cash moves in and out at different times within it. A profitable job can still run out of cash if subcontractors need paying well before the matching claim is received — exactly the gap a forecast exposes.
How do you build a construction cash flow forecast?
Start from a priced Bill of Quantities and the program, spread expected costs across the periods they will be incurred, then map expected progress claims against the dates they will be paid. Plotting both cumulatively shows the working capital gap at each point.
How often should a cash flow forecast be updated?
Regularly — monthly at minimum, and whenever the program, scope or payment terms change materially — so it keeps reflecting actual conditions rather than tender-stage assumptions.
What is the difference between a cash flow forecast and a budget?
A budget sets out the total expected cost and revenue for a project. A cash flow forecast goes further, showing when that money actually moves in and out over the timeline — revealing working capital gaps a budget alone will not show.
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