Yes, you can prepare a basic cash flow forecast for your building project yourself — and doing so is a smart move that helps you stay in control of your budget. However, the accuracy of your forecast depends heavily on how well you understand your contract, your builder's payment schedule, and the true costs involved. For larger or more complex projects, a professional quantity surveyor (QS) can add real value.
What Is a Cash Flow Forecast?
A cash flow forecast is a week-by-week or month-by-month projection of when money will leave your account during a building project. It maps your expected payments against the stages of construction, so you can make sure funds are available when your builder invoices you — and avoid nasty surprises like bridging finance costs or project delays caused by late payments.
It is different from a budget (which lists total costs) or a quantity surveyor's estimate (which values the work). A cash flow forecast is specifically about timing.
What You'll Need Before You Start
To build a useful forecast, gather the following:
- Your signed building contract — this will specify payment terms, progress payment stages, and any retentions
- Your builder's programme — a timeline showing when each stage of work is expected to be completed
- Your full project budget — including materials, labour, consents, professional fees, and a contingency allowance (typically 10–15% for residential builds)
- Your finance details — if you have a construction loan, your bank will have its own draw-down schedule and conditions
- Consent and inspection fees — check with your local council for current charges, as these vary by region
How to Build Your Forecast Step by Step
1. List All Cost Categories
Break your total project cost into categories such as:
- Design and consents
- Site preparation and foundations
- Framing and roofing
- Cladding and joinery
- Interior fit-out (linings, insulation, flooring)
- Plumbing, electrical, and mechanical services
- Landscaping and driveways
- Professional fees (architect, engineer, QS)
- Contingency
2. Map Payments to the Build Programme
Most residential contracts in NZ use progress payments tied to defined stages — for example, slab down, wall framing complete, roof on, lock-up, and practical completion. Use your builder's programme to estimate when each stage will be invoiced.
A simple table like this helps:
| Month | Stage | Estimated Payment |
|---|---|---|
| Month 1 | Consent fees, site prep | As per your budget |
| Month 2 | Foundation/slab | As per your budget |
| Month 4 | Framing complete | As per your budget |
| Month 6 | Lock-up | As per your budget |
| Month 9 | Practical completion | As per your budget |
Fill in your actual figures from your contract and budget.
3. Include Non-Construction Costs
Don't forget costs that fall outside the main build contract:
- Architect or designer fees (often invoiced monthly or at milestones)
- Engineer fees
- Council consent and inspection fees
- New service connections (power, water, wastewater) — contact your local lines company and council for estimates
- Temporary accommodation if you're displaced during the build
4. Account for Retentions
Many NZ contracts include a retention — typically 5–10% of each progress payment held back until defects are remedied after practical completion. Make sure your forecast shows this money being released at the end of the project, not earlier. The MBIE Building Performance website has useful guidance on construction contracts and your rights as an owner.
5. Align With Your Construction Loan Draw-Downs
If you're using a construction loan, your bank will release funds in tranches, usually after an inspection confirms each stage is complete. This can create a timing gap — your builder may invoice before the bank releases funds. Build a small buffer into your forecast to cover this lag. Talk to your bank early about their specific draw-down process.
Common Mistakes to Avoid
- Underestimating contingency — BRANZ research consistently shows NZ residential builds run over budget; 10–15% contingency is a minimum
- Forgetting GST — all contractor invoices will include GST; make sure your forecast figures are GST-inclusive unless you're GST-registered
- Ignoring programme delays — weather, material supply issues, and consent delays are common in NZ; build some schedule flexibility into your forecast
- Missing consent conditions — some councils require additional inspections or engineering sign-offs that cost extra; check your consent documents carefully
Spreadsheet Tools
A simple spreadsheet (Microsoft Excel or Google Sheets) is all you need. Set up columns for each month of the build and rows for each cost category. A running total row at the bottom shows your cumulative spend over time. This is your cash flow forecast.
When to Call a Professional
While a DIY forecast works well for straightforward projects, consider engaging a registered quantity surveyor if:
- Your project is large or complex (multi-storey, significant earthworks, commercial elements)
- You're uncertain about the reasonableness of your builder's pricing
- Your lender requires an independent QS report as a condition of your construction loan
- You want an independent check on progress payment claims before you pay them
- You're managing multiple contracts or a design-and-build arrangement
A QS can also prepare a cost plan and elemental estimate that gives your cash flow forecast a much more accurate foundation. You can find qualified quantity surveyors in your area on tradedirectory.co.nz.
Site Safe
Licensed Building Practitioner (LBP)
ISO 9001 / 45001 / 14001
NZ Institute of Building (NZIOB)
