Cash Flow Calculator
Project your monthly cash position and — if you are spending more than you bring in — how many months of runway you actually have left before the account hits zero.
- Updated Aug 17, 2026
- Reviewed by the BSF CPA Editorial Team
- US small business
- 9 min read
Runway collapses far faster than revenue falls. A business bringing in $82,000 a month against $76,000 of costs runs a comfortable $6,000 surplus. Drop sales 10% and it starts burning $2,000 a month — 25 months of runway on $50,000 of cash. Drop 15% and runway falls to 8.3 months; drop 20% and it is 5.0 months. The first 10% costs you everything; each further 5% roughly halves what is left.
Enter your opening cash, monthly income and each category of monthly outgoing, then the number of months to project.
Profit is opinion. Cash is fact. Many profitable businesses have failed because they ran out of cash. The Cash Flow Calculator forecasts your monthly net cash, projected closing balance, and — if you’re burning — how many months of runway remain. Use it weekly. It’s the most important spreadsheet you’ll ever build.
Cash Flow Calculator
Forecast monthly cash flow, runway, and closing balance — the survival metric for any business.
Cash Inflows (per month)
Cash Outflows (per month)
Cash Flow Forecast
How to read your results
| Output | What it means | Why it matters |
|---|---|---|
| Net monthly cash flow | Money in minus money out, each month | The single most important number. Positive means you are self-funding. |
| Total cash in | Monthly income × months projected | Sense-check against your sales pipeline. |
| Total cash out | Monthly outgoings × months projected | The commitment you are signing up to. |
| Closing balance | Opening cash + (net flow × months) | Where you end up if nothing changes. |
| Runway | Opening cash ÷ monthly burn | Months until cash reaches zero. Shows only when burning. |
| Status | Positive or Burning Cash | Positive at exactly break-even; anything below is burning. |
Cash is not profit
A profitable business can run out of money, and this is one of the more common ways good companies fail. Profit is an accounting measure that recognises revenue when earned and costs when incurred. Cash is what is actually in the bank on the day the rent is due.
The gap between them comes from timing. You buy stock in March and sell it in June. You invoice in April on 60-day terms and get paid in June. Depreciation reduces profit without touching cash; a loan repayment drains cash without touching profit. A business growing quickly can be highly profitable and simultaneously running out of money, because growth consumes cash before it produces any.
This calculator works entirely in cash. Enter money that actually moves, in the month it actually moves.
The formula
monthly cash out = COGS + salaries + rent + operating expenses + loan payments + tax
net monthly cash flow = cash in − cash out
closing balance = opening cash + (net cash flow × months)
runway = opening cash ÷ monthly burn (only when net flow is negative)
- in Cash actually received, not invoiced. Unpaid invoices are not income yet.
- out Cash actually paid. Include the full loan payment, principal as well as interest.
- runway How long the opening balance lasts at the current burn rate.
Runway displays as a dash whenever net cash flow is zero or positive, because there is nothing being consumed. Break-even exactly — cash in equal to cash out — is reported as Positive.
Runway and why it collapses
This is the behaviour worth internalising. Take a business with $50,000 of opening cash, $82,000 of monthly income and $76,000 of monthly costs, and vary only the sales line:
| Sales change | Monthly sales | Net cash flow | Runway |
|---|---|---|---|
| +10% | $88,000 | +$14,000 | Not burning |
| +5% | $84,000 | +$10,000 | Not burning |
| Base | $80,000 | +$6,000 | Not burning |
| −5% | $76,000 | +$2,000 | Not burning |
| −10% | $72,000 | −$2,000 | 25.0 months |
| −15% | $68,000 | −$6,000 | 8.3 months |
| −20% | $64,000 | −$10,000 | 5.0 months |
Between +10% and −5% the business is comfortable. At −10% it is burning. At −20% it has five months. A 20% revenue decline did not remove 20% of the buffer — it converted an indefinitely sustainable business into one with a deadline.
The reason is arithmetic: runway divides a fixed opening balance by the burn, and the burn is a small difference between two large numbers. Once income drops below costs, every further decline lands entirely on that small difference and shrinks runway hyperbolically.
The practical consequence: if you are within 10% of break-even, you are much closer to a cash crisis than the headline numbers suggest. Model the downside before you need to.
Three worked examples
$50,000 opening; $80,000 sales + $2,000 other; $76,000 total monthly costs; 12 months
Net cash flow +$6,000 a month. Over a year, $984,000 in and $912,000 out, closing at $122,000. Status Positive, no runway figure because nothing is being consumed. The business more than doubles its cash cushion in a year.
$150,000 opening; $25,000 sales; $75,000 total monthly costs; 12 months
Burning $50,000 a month against $150,000 in the bank — a runway of exactly 3.0 months. The 12-month closing balance shows −$450,000, which is not a forecast so much as a measure of the funding gap: the business ceases to exist at month three unless something changes.
$40,000 opening; $70,000 sales; $74,000 total monthly costs; 12 months
Burning just $4,000 a month, which sounds manageable, and the runway is 10.0 months. But this is the dangerous zone: the business is only 6% of revenue away from break-even, and equally only a small decline away from a three-month runway. Small numbers, short fuse.
Which lever buys the most time
Starting from a business burning $16,000 a month on $50,000 of cash — a 3.1-month runway — here is what each intervention actually buys:
| Action | New burn | New runway | Time bought |
|---|---|---|---|
| No change | −$16,000 | 3.1 months | — |
| Cut operating expenses 50% | −$13,000 | 3.8 months | +0.7 |
| Cut cost of goods 10% | −$12,000 | 4.2 months | +1.1 |
| Cut salaries 20% | −$12,000 | 4.2 months | +1.1 |
| Raise sales 10% | −$10,000 | 5.0 months | +1.9 |
Halving operating expenses — painful, visible, and usually the first thing cut — bought three weeks. A 10% sales increase bought nearly two months. When you are burning cash the instinct is to cut, but cuts are bounded by what you spend while revenue is not. That said, sales take time to move and costs can be cut this week, which is why serious situations need both.
What the projection assumes
In Example 2 the twelve-month closing balance reads −$450,000. No bank account does that. The projection continues spending after cash runs out, so treat a negative closing balance as the size of the gap you need to fund, not a prediction. The runway figure is the real deadline.
Every month is assumed identical — same income, same costs. Real businesses have seasonal peaks, quarterly tax payments, annual insurance renewals and lumpy stock purchases. For a seasonal business, run the calculator separately on your worst quarter's figures; that is the period that determines whether you survive.
Common mistakes
Entering invoiced sales, not collected cash
Money owed is not money available. If you invoice on 30-day terms, this month's cash reflects last month's sales.
Entering only loan interest
The whole payment leaves your account. Principal is invisible on the profit and loss but very visible in the bank.
Forgetting quarterly and annual outgoings
Tax payments, insurance renewals and licence fees arrive in lumps. Divide them by twelve and include them monthly.
Treating a small burn as safe
Example 3 burns only $4,000 a month, but it sits 6% of revenue from break-even in one direction and a cash crisis in the other.
Ignoring owner drawings
If you take money out of the business, that is cash out. Leaving it out produces a runway you cannot actually live on.
Modelling only the expected case
The base case rarely kills a business. Run it at 10%, 15% and 20% below plan — that is where the cliff is.
Best practices
Update it monthly
Cash position moves faster than any other business metric. A forecast three months old is a historical document.
Know your number before you need it
Raising money or arranging credit takes months. If runway is under six, start the conversation now rather than at month two.
Model your worst quarter, not your average
Averages hide the month you cannot pay. Seasonal businesses should test the trough in isolation.
Attack collections first
Getting paid faster improves cash without cutting anything or selling more. It is usually the quickest available lever.
Frequently asked questions
What is cash runway?
The number of months your current cash lasts at your current burn rate — opening cash divided by net monthly outflow. It only appears when you are spending more than you receive.
Why is my business profitable but short of cash?
Timing. Profit recognises a sale when you make it; cash arrives when the customer pays. Stock purchases, loan principal and slow collections all drain cash without appearing as costs on the profit and loss.
How much runway should I have?
Six months is a common minimum for an established business; funded startups usually target twelve to eighteen between raises. Below three months, cash management becomes the main job of running the company.
Should I enter invoiced or collected sales?
Collected. This is a cash forecast. If customers pay on 30-day terms, the cash arriving this month reflects the sales you made last month.
Do I include the whole loan payment?
Yes — principal and interest together, because the full amount leaves your account. Only the interest portion is an expense for profit purposes, but this calculator is measuring cash.
Why does the closing balance go negative?
The projection keeps applying the monthly flow for the full period you entered, even after cash reaches zero. Read a negative closing balance as the size of the funding gap; the runway figure is the actual deadline.
How do I handle a seasonal business?
Run it separately for your weakest period using that period's figures. An annual average can show a comfortable position while a specific quarter runs you out of money.
What counts as other income?
Cash coming in that is not trading revenue — grants, interest received, tax refunds, asset sales, owner contributions. Anything that lands in the account and is not a customer payment.
Should owner drawings be included?
Yes, under operating expenses or salaries. Money you take out is cash the business no longer has, and a forecast that omits it overstates your runway.
What is the fastest way to extend runway?
Usually collections — invoicing promptly and chasing overdue accounts converts existing sales into cash without new revenue or cuts. After that, deferring non-essential spending, then negotiating supplier terms.
Does this account for growth?
No. Every month uses the same figures. If you expect growth, run the calculator at a few different revenue levels rather than assuming one path — and remember that growth itself consumes cash before it generates any.
Is break-even reported as positive?
Yes. Cash in exactly equal to cash out shows as Positive with no runway figure, because nothing is being consumed. It is stable, but it has no capacity to absorb a bad month.
Methodology & sources
Monthly cash in is sales receipts plus other income; monthly cash out is the sum of cost of goods, salaries, rent, operating expenses, loan payments and tax. Net monthly cash flow is the difference, and the closing balance applies it across the projection period without stopping at zero. Runway divides opening cash by the monthly outflow and is shown only where net flow is negative; status reports Positive at or above break-even. All months are assumed identical, with no seasonality, growth or one-off items, and the model is entirely cash-based — it does not reflect accruals, depreciation or other non-cash accounting entries. Negative balances display with the currency symbol before the minus sign; this is formatting only and the figures are correct.
- Standard cash flow forecasting practice as applied in US small business financial management.
- US Small Business Administration — cash flow management and forecasting guidance.
- All figures independently modelled and verified against the live calculator.
Related resources
- Working Capital CalculatorThe balance sheet view of liquidity
- Break-Even CalculatorThe sales volume that stops the burn
- Profit Margin CalculatorWhether each sale actually contributes
- Markup CalculatorPricing that funds the cycle
- Payback Period CalculatorBefore committing cash to an asset
- All CalculatorsThe full BSF library
Run the downside before you need it
Model your revenue 10%, 15% and 20% below plan. If runway drops below six months in any of them, act now rather than later.
Goes deeper on this
13-Week Cash Flow Forecast (Excel)
The rolling quarter-ahead forecast lenders ask for and owners actually use. It flags the week you run short, not the week after.
Email me this result
We will send the numbers this page just showed you, plus a link back to it. No account needed.
Keep exploring
