Free cash flow forecast calculator for Australian small businesses. Start from your opening cash balance, add your average monthly cash in and cash out, and project a month-by-month table of opening, in, out and closing balances over 3, 6 or 12 months. The calculator flags any month your closing balance is forecast to go negative so you can act before you run out of cash — the timing gap that catches out even profitable businesses.
What's in your bank account today
Customer payments actually received per month
Wages, rent, suppliers, super, BAS — paid per month
Net monthly cash flow
+$0.00
Building cash each month
Balance after 6 months
$0.00
Lowest projected balance
$0.00
Stays positive
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A cash flow forecast projects the actual money moving in and out of your bank account, month by month. Unlike a profit figure, it ignores invoices you've raised but not yet collected and bills you've incurred but not yet paid — it tracks only real cash movements. That makes it the single best early warning of a cash shortfall.
For every month the maths is the same:
Say you start with a $10,000 opening balance, expect $25,000 of cash in each month and $28,000 of cash out each month. Your net cash flow is −$3,000 per month. Month 1 closes at $10,000 + $25,000 − $28,000 = $7,000; Month 2 at $4,000; Month 3 at $1,000; and Month 4 at −$2,000 — so the forecast warns you that you'll run short in Month 4 and need to act before then.
Cash in is money actually received: customer payments (not invoices issued), deposits, loan drawdowns, and tax refunds. Cash out is money actually paid: wages and super, rent, supplier bills, loan repayments, equipment, and tax payments such as your quarterly BAS/GST and PAYG instalments. Timing matters — record GST and tax as cash out in the month they're paid to the ATO, not the month they're incurred.
If the forecast dips below zero, you have time to fix it: bring cash in forward (take deposits, invoice faster, shorten payment terms, chase overdue accounts), push non-urgent cash out back, arrange an overdraft or finance, or trim discretionary spending. A forecast's whole value is giving you those weeks of warning.
A cash flow forecast is a month-by-month projection of the money expected to flow into and out of your business. Starting from your current (opening) cash balance, you add the cash you expect to receive and subtract the cash you expect to pay out each month to work out your closing balance — which becomes the opening balance for the next month. It shows whether you can cover wages, rent, the ATO and suppliers before the money actually moves.
Start with your opening cash balance (what's in the bank today). For each month, add your expected cash in (customer payments, not just invoices issued) and subtract your expected cash out (wages, rent, super, GST, supplier bills, loan repayments). The running closing balance for each month tells you when cash gets tight. This calculator does that maths for 3, 6 or 12 months so you can spot a shortfall early.
Profit is income minus expenses on an accounting basis — it can include invoices you've raised but haven't been paid for. Cash flow is the actual movement of money in and out of your bank account. A profitable business can still run out of cash if customers pay slowly while wages, rent and the ATO fall due. That timing gap is exactly what a cash flow forecast is designed to expose.
A negative closing balance means your forecast cash out exceeds your opening balance plus cash in for that month — in plain terms, you're projected to run out of money. Common causes are seasonal dips in sales, large one-off payments (a BAS/GST bill, super, insurance, equipment), or customers paying later than you pay your own bills. The fix is usually to bring cash in forward (deposits, faster invoicing, shorter payment terms) or push non-urgent cash out back.
Most small businesses review their forecast monthly and refresh it whenever something material changes — winning or losing a big job, a price rise, hiring, or a tax bill landing. Treat it as a rolling document: each month, replace your forecast figure with what actually happened and roll a new month onto the end. A forecast is only useful while it reflects reality.
Yes. GST you collect on sales is your cash in the short term, but you hand it to the ATO at BAS time, so it's cash out later — many businesses are caught short by quarterly GST and PAYG instalments. Include your expected BAS payment, super guarantee, and income tax instalments as cash out in the months they're actually due, not when they're incurred, so your forecast reflects real bank movements.
Sources & methodology
This calculator runs a simple deterministic cash flow projection. It starts from your opening cash balance and, for each month, adds your average monthly cash in and subtracts your average monthly cash out to produce a closing balance, which carries forward as the next month's opening balance. It flags any month whose closing balance falls below zero. It assumes your average monthly figures stay constant — real businesses vary month to month, so treat the result as a planning guide, not a guarantee. Everything is computed in your browser; nothing you enter is stored or sent to a server.
Authoritative sources
Reviewed by Bishal Shrestha — Founder of OneBookPlus, 10+ years building tools with Australian tax-agent and BAS-agent practices. Last reviewed and updated: June 2026.
Disclaimer: This tool provides estimates only and is not professional advice. For decisions that affect your tax, finances, or compliance position, consult a registered professional.
OneBookPlus handles invoicing, GST tracking, BAS prep, and ATO lodgement automatically.