Free Cash Flow Calculator
More small businesses fail from running out of cash than from being unprofitable. This free cash flow calculator projects twelve months of cash in, cash out and closing bank balance, then answers the question that actually keeps owners awake: how long until I run short, and how bad does it get before it gets better?
It runs entirely in your browser, requires no sign-up, and nothing you type leaves your device.
Profit Is Not Cash
A profit and loss statement records revenue when you earn it. A bank account records money when it actually arrives. That gap is where businesses die. You can invoice $100,000 in March, book a healthy profit, and still be unable to make April payroll because your customers pay on Net-60 terms.
That is why this tool asks for cash collected, not revenue invoiced, and cash paid, not expenses incurred. Loan principal repayments, tax payments and equipment purchases all drain cash without ever appearing as expenses on your P&L. Model what leaves the bank.
How the Projection Works
The model is deliberately simple, which makes it easy to sanity-check. You give it four numbers: your opening cash balance, your typical monthly cash in, your typical monthly cash out, and a growth rate for each side. It then compounds each side independently, month by month:
- Cash in, month n = starting inflow × (1 + inflow growth)^(n − 1)
- Cash out, month n = starting outflow × (1 + outflow growth)^(n − 1)
- Closing balance = previous balance + cash in − cash out
Giving inflows and outflows separate growth rates matters more than it sounds. If your costs grow faster than your revenue, no amount of sales growth saves you — the gap simply widens every month, and the calculator will say so.
A Worked Example
Take a business with $25,000 in the bank, collecting $40,000 a month and paying out $42,000 a month. Inflows are growing 4% a month; outflows 2%.
Month one is a $2,000 loss of cash, dropping the balance to $23,000. Month two loses about $1,240, month three about $430. But because inflows compound faster than outflows, month four turns positive — and from there the balance climbs steadily.
The critical number is not the ending balance. It is the lowest point: roughly $21,300 in month three. That is the moment of maximum strain, and the moment a surprise tax bill or a late-paying client would break you. The calculator flags it explicitly, because a projection that only shows the happy ending is worse than useless.
Cash Runway and Burn Rate
Your burn rate is how much cash you lose in an average month. Your runway is how many months until the balance hits zero at that burn. If you are burning $5,000 a month with $30,000 in the bank, you have roughly six months of runway.
Runway is the deadline for every plan you have. It tells you when a financing conversation must start, not when it would be nice to. If the calculator reports that your balance goes negative in month seven, then month four is when you talk to a lender — not month seven, when you have no leverage and no time.
To extend runway you can raise prices, collect faster, delay non-essential spending, or bring in financing. Invoice factoring and a business loan are both options worth modelling — the tools linked below will price them for you.
What This Model Does Not Do
Simplicity is the point, but be clear about the trade-offs. This projection assumes smooth, steady growth on both sides. It does not model seasonality, a large one-off equipment purchase, quarterly tax payments, a customer who pays 90 days late, or a financing draw arriving mid-year.
Use it to understand the shape of your cash position and to find the danger month. Then, if the picture is tight, build a proper month-by-month forecast with your actual expected timing — or ask your accountant to. A model that is roughly right beats a spreadsheet that is precisely wrong, but neither replaces knowing when your customers really pay.