A profitable residential job can still put pressure on the business account if the money leaves before the next progress claim lands. To forecast construction cashflow properly, a builder needs more than a tender total and a rough build duration. You need a measured cost base, realistic trade payment timing, client claim dates, and a construction programme that reflects how the work will actually be built.
For a granny flat, custom home, duplex or triplex, cashflow is usually won or lost in the gaps: an early materials deposit, a large excavation account, a delayed frame claim, or a subcontractor invoice that arrives well ahead of its matching client payment. The answer is not to add a blanket contingency percentage and hope. It is to model the timing of each major inflow and outflow before the contract is signed.
What a construction cashflow forecast must show
A cashflow forecast is a time-based view of money, not another version of the estimate. The estimate answers, "What should this project cost?" The cashflow forecast answers, "When will we pay it, when will we receive it, and what funding gap will the business carry?"
At a minimum, the forecast should show weekly or monthly opening cash, client receipts, direct project costs, site overheads, closing cash and cumulative position. Monthly forecasting is often enough at tender stage. For a short or cash-tight project, switch to weekly periods once the job is awarded, particularly through site establishment, groundworks, frame and lock-up.
The forecast also needs to distinguish committed costs from expected costs. A signed concrete quote and an issued timber order are commitments. A provisional allowance for rock excavation or authority works is an expected cost with a different level of certainty. Combining the two hides risk exactly where the business needs visibility.
Start with a measured BOQ, not a percentage of contract value
A cashflow model is only as credible as the estimate beneath it. Broad square-metre rates and trade percentages can be useful for a quick early feasibility check, but they do not provide enough detail to schedule cash with confidence. They cannot tell you whether the structural steel package is due before the frame claim, whether joinery has a 50 per cent deposit, or whether external works sit outside the main build sequence.
Build the forecast from a measured BOQ structure. Break the estimate into trade packages and cost codes that match the way you buy and manage the work: preliminaries, demolition, earthworks, concrete, framing, roofing, cladding, windows, rough-ins, linings, joinery, finishes and external works. Then separate measured scope from provisional allowances.
That separation matters. Measured quantities can be priced using current rate cards and tested against subcontractor pricing packs. Provisional allowances should be flagged with an assumption, an expected timing window and an owner. If a sewer upgrade, retaining solution or latent site condition is not resolved at tender, do not quietly spread it through the build cost. Make its cash exposure visible.
Map each cost to programme logic
The construction programme turns the BOQ from a cost report into a cashflow forecast. Each trade package needs a planned start date, duration, procurement lead time, deposit point, progress payment point and final payment point. The value does not always fall evenly across the duration of the activity.
Windows are a common example. The installation may occur around lock-up, but the supplier may require a deposit when shop drawings are approved and the balance before delivery. Joinery, steel, trusses, roofing and some flooring packages can create the same issue. If the programme only places the full cost in the installation month, the forecast will understate the early funding requirement.
Preliminaries need the same discipline. Site supervision, temporary fencing, amenities, insurance, skip bins, scaffold and site establishment do not appear in one clean trade claim. Some are upfront, some are recurring, and some extend if the programme slips. Forecast them by the actual cost pattern rather than treating preliminaries as a single tender line.
A useful working approach is to assign each package a payment profile. For example:
| Package | Typical cash timing to model | | --- | --- | | Earthworks and concrete | Early mobilisation, then progress claims through slab completion | | Frame and trusses | Deposit or supply payment before installation, balance at frame stage | | Windows and doors | Deposit on approval, balance before or at delivery | | Plumbing and electrical | Separate rough-in, fit-off and final payments | | Joinery | Deposit after selections, progress payment before delivery, final after install |
The exact profile depends on your supplier terms, location and buying power. Regional delivery constraints or limited trade capacity can shift deposits earlier than a metro programme suggests. Use the subcontractor's actual terms wherever possible, not an assumed industry average.
Align client claims with the cost curve
A job may look cash-positive on a standard progress-payment schedule but become negative when actual trade and supplier timing is applied. This often happens around frame and lock-up, where procurement commitments accelerate while certification, variations or lender processing slow the receipt.
Load the forecast with the contract claim schedule, including the expected claim date, assessment period and realistic receipt date. A claim issued on the 25th is not cash on the 25th. Include the contractual payment terms and allow for the client's funding process where that is known. Do not make the forecast look healthier by assuming every claim is paid on the earliest allowable day.
Variations require their own line. Approved variations can improve the project margin, but they do not improve cashflow until they are claimed and paid. Pending variations should be tracked separately from both base-contract receipts and committed costs. If work must proceed before approval to protect the programme, identify the temporary funding exposure clearly.
Retention is another common blind spot. Retention withheld from progress claims is not operating cash available to pay trades. Show it as a separate future receipt, timed to practical completion or the defects liability release point under the contract. The same principle applies if you retain funds from subcontractors: do not rely on that balance to mask a weak project cash position.
Test the forecast before it becomes a problem
The first forecast is a base case, not a promise. Before accepting the job, test the periods where cumulative cash is lowest and run a few commercially realistic scenarios. You are looking for the point at which the project demands the most working capital, not simply whether the final margin is acceptable.
Test at least the likely causes of movement: a four-week programme extension, delayed client payment, an earlier supplier deposit, a provisional allowance exceeding budget, and a trade package landing above the rate-card allowance. On duplexes and triplexes, also test staging. Separate dwellings may create opportunities to claim earlier, but only if the programme, contract and certifier requirements genuinely support that sequence.
If the downside case creates a funding gap you cannot comfortably carry, act before contract execution. You may need to revise procurement timing, negotiate supplier terms, adjust the claim schedule where the contract allows, reduce exposure through earlier selections, or hold a clearer provisional allowance. The right move depends on the job. Pushing every supplier for longer terms can damage pricing or reliability, while bringing forward claims without matching completed value can create a dispute.
Keep it live once the project starts
Tender-stage cashflow is a decision tool. Live cashflow is a control tool. Update it at least monthly against actual invoices, committed purchase orders, revised programme dates, approved variations and claim receipts. On a project with tight working capital, update it weekly.
The key is to retain the original forecast alongside the current view. If earthworks run over, you need to see whether the issue is a cost overrun, a timing shift, or both. If windows are ordered earlier to protect the programme, the estimate may remain unchanged while the cash requirement rises sharply. Treat those as different management actions.
A builder-ready estimating pack makes this far easier. An editable BOQ workbook gives you a structured cost base; subcontractor pricing packs help confirm package terms; and an indicative construction programme provides the sequence needed to time the spend. EstiFlow produces those inputs from DA-stage plans in under three hours, so the cash discussion can happen while the tender decision still has value.
The best cashflow forecast is not the one with the neatest graph. It is the one that tells you, early enough, which fortnight needs attention and what commercial decision will protect the job.