Runway is the number of months your business can keep operating with the cash it has now, before it needs new revenue, a loan or fresh investment. To calculate runway, divide the cash you can actually spend by your net monthly burn, which is how much more cash goes out each month than comes in. It's the clearest early warning an owner has.
This guide is for owners who are spending more than they bring in right now, whether that's a new business still ramping up, an established one in a rough patch or a company funding a big expansion. You'll learn the honest version of the formula, how growth changes the picture, and what to do at each runway milestone.
The runway formula, and the two burn numbers behind it
The basic formula is short:
- Runway (months) = usable cash ÷ net monthly burn
- Gross burn = total cash going out in a month (payroll, rent, suppliers, loan payments, everything)
- Net burn = gross burn − cash coming in from customers that month
Gross burn tells you what it costs to keep the lights on if revenue stopped entirely. Net burn is what's actually draining the account. Use net burn for runway, but keep gross burn in view, because it's your worst case if a big customer leaves or a season collapses.
If net burn is zero or negative, meaning more cash comes in than goes out, you don't have a runway problem. You have a business that funds itself, and your attention belongs on building a cash reserve that fits your risk.
What counts as "usable cash"
This is where most runway numbers go wrong. The balance in your bank account is not the same as the cash you can spend. Start with the bank balance, then:
- Subtract a floor you won't go below. You need enough to cover at least one payroll plus a cushion for timing surprises. Pick a number and treat it as untouchable.
- Subtract known lumps. Annual insurance renewals, quarterly estimated taxes, a balloon loan payment or a lease deposit coming up in the runway window.
- Subtract money that isn't yours. Sales tax you've collected, customer deposits for work not yet done, and payroll taxes withheld but not yet remitted.
- Add only committed cash. An approved, undrawn line of credit can count if you're comfortable using it. A loan you've applied for cannot.
Worked example: a new fitness studio in its first year
Imagine a hypothetical boutique fitness studio eight months after opening. It has $84,000 in the bank. Here are its monthly cash outflows:
- Rent: $12,000
- Payroll for coaches and front desk: $19,500
- Equipment lease: $2,800
- Utilities: $2,400
- Software and marketing: $3,100
- Insurance (monthly portion): $1,200
Gross burn: $12,000 + $19,500 + $2,800 + $2,400 + $3,100 + $1,200 = $41,000. Membership revenue collected is $29,000 a month, so net burn is $41,000 − $29,000 = $12,000.
The naive runway
$84,000 ÷ $12,000 = 7 months. That's the number most owners stop at.
The honest runway
The owner decides never to let cash drop below $15,000, roughly three weeks of payroll plus rent. There's also a $6,000 insurance deposit due in month three. Usable cash is $84,000 − $15,000 − $6,000 = $63,000. Honest runway: $63,000 ÷ $12,000 = 5.25 months.
That's nearly two months shorter, and those two months are exactly the ones you'd need to arrange financing calmly instead of in a panic.
How growth changes your runway
Dividing cash by burn assumes burn stays flat. For a business that's still ramping, it usually doesn't. Suppose the studio adds members steadily. Here's what happens to the full $84,000 under three scenarios, ignoring the floor and deposit to keep the comparison clean.
| Scenario | Revenue change each month | What happens to cash |
|---|---|---|
| Flat | $0 | Burns $12,000 every month. Cash runs out after month 7. |
| Slow growth | +$750 | Burn falls from $11,250 to $3,000 by month 12. Cumulative burn reaches $82,500 after month 11 and passes $84,000 during month 12. Break-even would not arrive until month 16. |
| Faster growth | +$1,500 | Burn falls from $10,500 to zero in month 8. Cumulative burn is $42,000, so cash bottoms out around $42,000 and then starts rising. |
To check the fast-growth row: the monthly burns are $10,500, $9,000, $7,500, $6,000, $4,500, $3,000 and $1,500, which add up to $42,000, and month 8 is zero. The lesson is that growth rate matters as much as the cash balance. A studio adding $1,500 a month in revenue survives comfortably. The same studio adding $750 a month runs out just before break-even, which is the worst possible time.
That's why runway should be modeled month by month rather than calculated once. A 13-week cash flow forecast handles the near term, and a simple 12-month projection covers the rest. To test your own scenarios quickly, try our cash runway calculator.
What to do at each runway milestone
Runway is only useful if it triggers action. Here's a decision rule you can adapt:
| Honest runway | Status | What to do now |
|---|---|---|
| More than 12 months | Comfortable | Track monthly. Open a line of credit while you don't need it, because lenders prefer borrowers who aren't desperate. |
| 6 to 12 months | Plan | Build a written plan with specific cost cuts and revenue moves you'd make, and the date you'd make them. Start financing conversations. |
| 3 to 6 months | Act | Execute the plan. Cut discretionary spending, pause hiring, push collections, renegotiate payment terms with suppliers. |
| Under 3 months | Emergency | Make structural decisions: reduce staff hours, sublease space, sell unused equipment, talk to your lender and your accountant this week. |
The reason to act early is simple. Every option gets worse as runway shrinks. Loans are harder to get, suppliers are less flexible and cost cuts have less time to take effect.
Ways to extend runway, ranked by speed
- Collect faster (days to weeks). Chase overdue invoices, require deposits, switch recurring customers to automatic payment.
- Delay outflows (weeks). Ask key suppliers for longer terms, move equipment purchases out a quarter, pause nonessential subscriptions.
- Cut fixed costs (one to three months). Renegotiate rent, drop underused software, restructure staff schedules. These take time to show up but last.
- Raise prices (one to three months). Often the most powerful lever, because each dollar goes almost straight to reducing burn.
- Add financing (weeks to months). A loan or line of credit buys time, but only helps if the business can eventually cover the payments.
For a longer list of levers, see our guide on how to improve cash flow in a small business.
Common runway mistakes
- Using the bank balance as usable cash. Collected sales tax, customer deposits and withheld payroll taxes aren't yours to spend. Subtract them.
- Using profit instead of cash. Your income statement may show a small loss while cash drains much faster because of loan principal, inventory buys or slow collections. Burn must come from cash movement.
- Averaging over seasonal months. If you burn $20,000 in January and gain $10,000 in June, an average hides the danger. Model the actual months ahead.
- Forgetting lumpy payments. Annual insurance, quarterly taxes and equipment deposits can knock a month or more off runway in one hit.
- Assuming growth that hasn't happened. Model the flat scenario too. If it's scary, act on it rather than hoping the optimistic line comes true.
- Calculating it once. Recalculate monthly. Runway changes fast when burn is high.
Where AI can help
AI assistants are handy for the grunt work of runway modeling. Export three to six months of bank transactions, ask an assistant to group outflows into categories and separate one-off payments from recurring ones, and have it draft a month-by-month table under two or three growth assumptions. It can also scan your transaction history for annual or quarterly charges you've forgotten about.
Check its categories against reality, though. It won't know that one large payment was a one-time deposit or that a customer's big payment was a prepayment for next year. You still decide which assumptions are realistic.
Frequently asked questions
What's a good runway for a small business?
For a business that's burning cash, many advisors suggest aiming for enough to reach break-even plus a cushion, because what matters is whether you'll get there before cash runs out. For a profitable business, "runway" becomes your reserve, and a few months of fixed costs is a common starting target.
Should I count my line of credit in runway?
You can, as a separate line. Calculate runway with and without it. The version without it tells you when you'll start borrowing, and the version with it tells you when you'll truly run out.
Does owner pay count as burn?
Yes, if you need it to live. Leaving your own pay out makes runway look longer, but if you can't actually go without it, the math is fiction.
How is runway different from break-even?
Break-even is the sales level where you stop losing money. Runway is how long you can last before you get there. You need both: one is the destination, the other is your fuel gauge.
Key takeaways
- Runway = usable cash ÷ net monthly burn.
- Usable cash excludes your safety floor, known lump payments and money you're holding for others.
- Growth rate changes runway dramatically, so model it month by month rather than with one division.
- Set runway milestones in advance and tie each one to specific actions.
- Collecting faster and raising prices usually extend runway faster than cutting costs.
- Recalculate every month while you're burning cash.
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