What your numbers say:
Conditional arithmetic on three levers
Each line is conditional arithmetic: it holds only if the change you entered actually happens and nothing else moves. It is not a forecast and not a recommendation.
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Everything on this page comes out of the five numbers you typed. There is no benchmark database behind it, no industry average, no model. Start at the top: cash in the bank today, average monthly revenue, monthly fixed costs, variable costs as a percentage of revenue, and your monthly draw. The calculator multiplies revenue by your variable percentage to get variable cost, then subtracts variable cost, fixed costs, and your draw from revenue to get your net monthly position. If that number is negative, the size of the negative is your monthly burn, and your runway is the cash you have divided by that burn.
Three assumptions are baked in and you should know about them. First, the variable cost percentage is held constant, so if your shipping or ad cost ratio moves, the runway moves with it. Second, revenue is held flat at your average month, which is what makes the six and twelve month figures a simple linear projection: your cash today plus the net monthly position you just computed, carried forward six or twelve times. It is not a forecast, not a seasonal model, and not a growth projection, so read it as straight line arithmetic from this month rather than as a prediction of what your bank balance will be. Third, the break even figure divides your fixed costs plus your draw by whatever share of a revenue dollar is left after variable cost, and it is capped at a 95% variable ratio so the division cannot break. The three lever boxes at the bottom of the form are your own assumptions too, entered by you, and every lever line is conditional on that change happening exactly as you entered it with nothing else moving.
One more assumption worth naming: the cash out date is calculated from the real date you load this page, and a fraction of a month is converted at 30 days. A box you clear or type something unreadable into falls back to the default number printed in it, so a blank fixed cost box is treated as 12,000 rather than as zero. This is arithmetic on the numbers entered. It is not financial, tax, or investment advice, and nobody has looked at your accounts.
A worked example with the default numbers
Take the defaults: $24,000 in the bank, $18,000 revenue a month, $12,000 of fixed costs, variable cost at 35% of revenue, and a $4,000 draw. Variable cost is $18,000 multiplied by 0.35, which is $6,300. Net monthly is $18,000 minus $6,300 minus $12,000 minus $4,000, which is negative $4,300. So the burn is $4,300 a month, and runway is $24,000 divided by $4,300, which is 5.6 months. That puts cash reaching zero roughly five and a half months from today, and the six month position is negative $1,800. Break even needs $12,000 plus $4,000, which is $16,000, divided by 0.65, which is $24,615 a month in revenue. You entered $18,000, so the gap is $6,615 a month. The status band reads Act now, because 5.6 months lands in the three to six month range, and in practice that range means you have about half a year of decisions left before this stops being a decision at all.
When cash is tight, runway is the only number that matters
Growth rate, margin percentage, and annual profit are all useful and all secondary. They describe a business over a period long enough that it assumes survival. Runway measures the gap between now and the point where the decisions stop being available to you. A business doing 40% a year and holding 18 months of cash has more room to be wrong than a business doing 5% with 4 months of cash, and the first one can fix whatever is going wrong at a pace the second one cannot.
Runway also changes how every other decision reads. The same ad campaign is a reasonable test at eight months of runway and a coin flip at three. The same hire is a fixed cost that can be undone at nine months and a commitment you are stuck with at two. Once the number is on the screen you can see it move as you change the inputs, which makes it far more useful as a working tool than a figure you compute once and forget.
The four things that consume cash in a small business
Most small businesses that run out of money did not lose a dramatic amount. They lost four smaller amounts in the same quarter, and the calculator above is built around those four because they are what the inputs are actually measuring.
- Stock bought too early. Inventory is cash that has already left the bank and is sitting in a warehouse. It is the single largest line item for most ecommerce operators, and the one most often bought against a sales forecast that does not arrive. It shows up here as a variable cost percentage, and a percentage that rises when revenue falls is a business funding its own stock problem.
- Ad spend that lands after the money leaves. You pay the platform today, the customer pays you at the end of the month, and the gap in between is funded by you. Scale spend into a falling conversion rate and the gap widens fast. This is why runway can shrink faster than revenue does.
- A draw that never flexes. A founder draw treated as salary does not move when revenue moves, so a soft month removes the entire shortfall from your own income and nothing softens. It is the easiest line on this whole page to change, which is exactly why it is worth putting on the screen.
- Tax set aside late. Money that has been earned is not money you hold. When tax is set aside after the fact, the cash leaves in a lump at the worst possible moment. This calculator does not model tax at all, so treat the runway it shows as pre tax and set your own reserve inside it.
What to do next
Put your real numbers in, not round ones, and let the runway land where it lands. Then do one thing: find the input that moves the number most per dollar of effort, and change that one. The lever arithmetic at the bottom of the calculator is there to make that comparison honest. A cut to fixed costs lands on your net position one dollar for one dollar, a revenue lift lands at your contribution margin rather than at full price, and a reduction in variable cost percentage only helps you while revenue holds. They are not equally effective, and the calculator shows you the arithmetic rather than telling you which one to pick.
Two habits make this number worth keeping. Re-enter your real cash balance on the first of every month, because a month of drift is usually a month you did not know about. And treat anything under three months as a decision to make something different this month, not next quarter. If you want a second pair of eyes on where the money is actually going before you change anything, theBreak-Even ROAS Calculator runs the same kind of real numbers math on your ad economics, and theLTV to CAC Calculator checks whether the customers you are buying are worth what you are paying for them.