How to Build a 13-Week Cashflow Forecast: A Sydney Virtual CFO's Guide (2026)
A Sydney virtual CFO's guide to building a 13-week cashflow forecast: structure, line items, Australian tax and super timing, and the mistakes to avoid.
The 13-week cashflow forecast is the single most useful financial tool a founder can own, and most do not have one. The profit and loss statement is for your accountant. The annual budget is for your board. The 13-week is for you, because it answers the only question that can actually shut a business down: will there be enough cash in the bank, every week, for the next quarter. A profitable business with no cash visibility is one bad month from a crisis. A 13-week forecast is how you see the crisis coming with enough time to do something about it.
This is a practical guide to building one properly, with the Australian-specific timing that trips most founders up.
Published: June 2026
Thirteen weeks is one quarter, week by week. It is long enough to see the major cash events coming (a quarterly tax payment, a large supplier bill, a lumpy receivable) and short enough that each week's number is a real estimate rather than a guess. You build it rolling: each week you drop the week just gone, add a new week 13 at the end, and reforecast against what actually happened.
The critical distinction is cash versus profit. Your P&L records revenue when you earn it and costs when you incur them. Your bank account moves when money actually arrives or leaves, which can be weeks earlier or later. A business can post a profit and run out of cash in the same quarter, because customers pay late, suppliers want paying now, and tax falls due on its own schedule regardless of how trading is going. The 13-week forecast is built on cash timing, not accrual, and that is the whole point.
Every 13-week forecast has the same skeleton, repeated across thirteen weekly columns:
The discipline is in the line items underneath receipts and disbursements, and in timing each one to the week the money actually moves rather than the week it was invoiced or incurred.
Receipts are almost always where forecasts go wrong, because founders enter them based on when they invoiced rather than when they will be paid. Build receipts off collection behaviour:
For a business with lumpy revenue (construction progress claims, project-based consulting, large ecommerce wholesale orders), this is where the real risk sits, and where the forecast earns its keep.
Disbursements are more predictable but easy to under-scope. The lines that matter:
The test of a good disbursements section is simple: nothing surprises you. If a quarterly tax payment or a super run ever lands as a shock, the forecast was incomplete.
A Sydney services business has a healthy P&L and assumes cash is fine. Build the 13-week and week 7 lights up red. That week, payroll falls, a quarterly BAS payment is due, the super guarantee run lands, and the largest customer's payment is forecast a week late. Individually, each is routine. Stacked in one week, they overdraw the account by $60K.
Seen six weeks out, this is a non-event. The founder accelerates one large receivable, defers a discretionary supplier payment by a week, and the problem dissolves. Seen on the morning it happens, it is an emergency phone call to the bank from a position of weakness. Same business, same numbers, completely different outcome. The only variable is whether the cash was modelled. That is what the forecast buys you.
A single forecast line is half a tool. The value comes from running at least two versions side by side. The base case is your realistic expectation. The downside stress-tests it: your largest customer pays a month late, sales soften 20%, a project slips. Build the downside and you find your floor, the worst week in the quarter and how deep the hole goes, before it arrives rather than during.
The third layer is the one most founders skip: the action plan. For each pressure point the downside reveals, decide now what you would do. Which receivable would you chase first, which discretionary payment would you defer, at what point would you call the bank. A forecast that ends at "here is the problem" is diagnosis without treatment. The point of seeing the bad week six weeks out is to have already decided how you will handle it, so the response is a calm execution of a plan rather than a scramble.
The 13-week cashflow forecast is the most common deliverable we build, because it is the tool that most directly changes how a founder runs the business. Most Australian virtual CFOs would fold this into an open-ended retainer at $3K to $8K per month. We build it as a fixed-scope project instead.
Our front-door engagement, the 90-Day Number, is fixed scope, fixed fee, fixed timeline at $9,950 plus GST, with one named deliverable on day 90. For many businesses that deliverable is a fully built, scenario-tested 13-week cashflow forecast, handed over so your team can run and reforecast it. Led by a Chartered Accountant (CA ANZ). No retainer, no scope creep. On day 90 you own the model, and what comes next is your decision.
How is a 13-week cashflow forecast different from a budget?
A budget is an annual, accrual-based plan of revenue and costs. A 13-week forecast is a weekly, cash-based view of your bank balance over the next quarter. The budget tells you the plan; the 13-week tells you whether you can fund it week to week.
How often should I update it?
Weekly. Drop the past week, add a new week 13, and reforecast against actuals. The weekly rhythm is what keeps it accurate and what makes each estimate better than the last.
Can I build it in a spreadsheet?
Yes, and most are. The tool is not the hard part. The hard part is timing every line to actual cash movement and being honest about when customers really pay. That is the work, and where a virtual CFO adds the most.
What does the 90-Day Number deliver here?
A fully built, scenario-tested 13-week cashflow forecast as the named day-90 deliverable, handed over for your team to run. Fixed scope at $9,950 plus GST, no retainer.
Does Payday Super affect my forecast?
Yes, if your window crosses 1 July 2026. From that date super is paid with each pay run rather than quarterly, which moves a periodic lump cost into every cycle. Build the change in rather than discovering it.
My business is profitable. Do I still need this?
Profit and cash are not the same thing, and the gap between them is exactly where solvent, profitable businesses get caught out. The forecast is most valuable precisely when things look fine, because that is when nobody is watching the timing.
Sydney Virtual CFO is a Sydney-based virtual CFO service for founders running $3M to $15M businesses across SaaS, ecommerce, professional services, construction, and other low-volume, high-value industries. We deliver fixed-scope CFO engagements with a named deliverable on day 90: a 13-week cashflow forecast, a fundraise-ready financial model, a unit economics build, or a board reporting pack you can run on your own.
Our front-door product, the 90-Day Number, is fixed scope at $9,950 plus GST. We are one of the few project-based virtual CFOs in Australia, in a market built almost entirely on monthly retainers. No retainers without a deliverable. No 80-page reports. No theatre.
This content is general information only, written for Australian founders running businesses in the $3M to $15M revenue range. It does not constitute tax, financial product, investment, or legal advice and should not be relied on as such. The work referenced is led by a Chartered Accountant (CA ANZ), but Sydney Virtual CFO is not a licensed tax agent, not a licensed financial adviser, and not authorised to provide personal financial advice. Tax obligations, accounting treatments, fundraise terms, and statutory requirements depend on your individual circumstances. For advice specific to your business, contact the team directly or consult a registered tax agent, licensed financial adviser, or qualified lawyer. Information was current at the time of publication and may change without notice. We review and update guides periodically.
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