Cash Runway Calculator
How long can my business run on the cash it has?
Divide the cash above your safety reserve by what the business loses each month. The sample business below makes $900 a month, so today it never runs out — but with no sales at all its $38,000 above the reserve lasts 1.6 months · 51 days. That second number is the one to know.
Startup runway calculators assume a steady burn. A small business rarely burns steadily — it earns, and the danger is what happens when earnings stop or shrink. This one works from gross margin, so a sales drop also reduces the costs that move with sales, and it measures runway to your reserve, not to an empty account.
PassCash grows at today's pace. With no sales at all, the cash above your reserve lasts 1.6 months · 51 days.
| Monthly profit in cash terms | $900 | gross profit $23,400 minus every other monthly outflow |
|---|---|---|
| Cash above your reserve | $38,000 | cash today minus the reserve — the money that can actually be spent |
| Runway to your reserve | Does not run out | how long until cash touches the reserve at today's pace |
| Runway to zero | Does not run out | the same, all the way to an empty account |
| Runway with no sales at all | 1.6 months · 51 days | the reserve line at $22,500 a month of outflows and nothing coming in |
| Sales drop | Monthly sales | Monthly profit | Runway to reserve |
|---|---|---|---|
| 0% | $52,000 | $900 | Does not run out |
| 10% | $46,800 | -$1,440 | 26.3 months · 802 days |
| 20% | $41,600 | -$3,780 | 10.0 months · 305 days |
| 30% | $36,400 | -$6,120 | 6.2 months · 188 days |
| 50% | $26,000 | -$10,800 | 3.5 months · 107 days |
| 100% | $0 | -$22,500 | 1.6 months · 51 days |
Runs in your browser with fixed, tested formulas — the same exact arithmetic as the Business X-Ray. Nothing you type is sent or stored.
One question answered. Eight more are waiting.
This page tests one thing with a few monthly numbers. The Business Decision X-Ray runs your whole business through the same engine, day by day: nine tests, the exact breakpoint, the smallest repair and a dated action plan. Open demo of every section, no sign-up.
How this calculator works
Monthly profit in cash terms is sales × gross margin, minus every other monthly outflow. If it is positive, cash grows and the runway is open-ended. If it is negative, runway is the cash above your reserve divided by the monthly loss, expressed in months and days (365 ÷ 12 days to a month, rounded down so the answer never flatters you).
The table re-runs the same sum with sales 10%, 20%, 30%, 50% and 100% lower. Because it works from gross margin, only the gross profit is lost when sales fall — the direct costs of the lost sales disappear with them. Fixed outflows stay exactly where they are, which is what makes a sales drop dangerous.
The formula
Monthly profit = monthly sales × gross margin − other monthly outflows.
Runway (months) = (cash − reserve) ÷ −monthly profit, only when monthly profit is negative. Runway (days) = (cash − reserve) × 365 ÷ (−monthly profit × 12), rounded down.
Why runway to the reserve, not to zero
Zero is not where a business stops. It stops a week or two earlier, when payroll, rent or a supplier cannot be paid on the day. The reserve is your own line for that — a month of payroll, the next tax payment, whatever you never want to be without. The results show runway to the reserve and, separately, to zero; set the reserve to 0 and the table measures to an empty account too.
Worked example
The sample business sells $900 more than it spends each month, so the headline runway is open-ended. That is exactly the situation in which owners stop watching runway. Scroll to the table: a modest drop in sales turns the monthly profit negative, and with no sales at all the $38,000 above the reserve lasts 1.6 months · 51 days.
What this calculator does not do
- It uses monthly averages. Real cash moves on specific days: a payroll on the 28th and a customer who pays on the 5th can break the reserve inside a month that looks fine on average. The Business X-Ray models the day-by-day path.
- It assumes the same margin at every sales level and no seasonality.
- It does not include taxes due on a date, loan balloons or one-off payments unless you add them to monthly outflows.
Questions people ask
What is a good cash runway for a small business?
There is no universal number; it depends on how quickly sales can fall and how quickly you can cut costs. The useful test is the 'no sales' line: if the cash above your reserve would not cover the time it takes you to cut costs or find new work, the runway is too short for your business.
Is cash runway the same as burn rate?
No. Burn rate is how much cash leaves each month; runway is how long the cash lasts at that burn. This calculator derives the burn from sales, margin and outflows rather than asking you to guess it.
Should I include my own pay?
Yes. If you take money out of the business every month, it is an outflow like any other, and leaving it out makes the runway look longer than it is.
Why is my runway shorter than a startup calculator says?
Those calculators usually measure to zero and ignore the reserve. Measuring to the reserve is stricter on purpose: it is the point where you can no longer absorb a late payment.
Related decisions
- Sales Drop Calculator — How far sales can fall before you lose money — and before cash runs out.
- Customer Concentration Risk Calculator — Which customer's loss would put you in the red — and how fast.
- Can I Afford to Hire an Employee? — Month-by-month cash test of a new hire — and the most you can pay.
- 13-Week Cash Flow Calculator — Week-by-week cash for the next 13 weeks, and the first week that breaks.
- How long can my business survive without sales?
- How to stress test your small business cash flow
Formulas reviewed 26 September 2026
