Burn Rate and Runway: How to Calculate and Extend Them

Gross burn is every dollar of operating cash that leaves the business in a month: payroll, rent, software, contractors, marketing spend, everything on the cash flow statement's operating and investing lines except financing activity. It ignores revenue entirely. Net burn subtracts cash actually collected from customers in that same period from gross burn. A company billing $60,000 a month and spending $200,000 a month has gross burn of $200,000 and net burn of $140,000.

Founders often quote gross burn when they mean net burn, or the reverse, and the gap matters more as revenue grows. A pre-revenue company has identical gross and net burn, so the distinction feels academic. Once monthly revenue passes a few thousand dollars, the two numbers diverge, and an investor update that quotes gross burn without saying so overstates how fast the company is actually losing ground.

Both numbers should use cash collected and cash paid, not invoiced revenue and accrued expense. A SaaS company that invoices $80,000 in annual contracts up front but only recognizes $6,667 a month under ASC 606 revenue recognition should still burn against the $80,000 of cash in the bank that month, not the $6,667 of recognized revenue. Runway is a cash question. Mixing in accrual timing is the single most common way a founder ends up with a runway number that looks better on a slide than it is in the bank account.

A practical habit: pull both numbers straight from the bank feed and merchant processor, reconciled monthly, rather than from a budget-versus-actual spreadsheet built on assumptions. The bank balance does not lie about timing; a forecast can.

Runway in months equals current unrestricted cash divided by average monthly net burn over a recent, representative period, usually the trailing three months. A company with $900,000 in the bank and net burn of $150,000 a month has six months of runway.

The formula breaks down in three common ways. First, using a single month's burn instead of a trailing average: a month with an annual insurance renewal or a one-time contractor payout will understate runway, and a month right after an enterprise deal closes will overstate it. Second, ignoring known lumpy items ahead: a payroll tax true-up, a lease deposit, an annual software renewal, none of which show up in a trailing average but all of which hit cash on a specific date. Third, treating restricted or committed cash as available: a security deposit, an escrow balance tied to an acquisition earnout, or a line of credit that has already been drawn against a covenant should not count toward runway.

Worked example. A company has $1,200,000 in the bank. Trailing three-month average revenue collected is $70,000 a month. Trailing three-month average operating cash spent is $220,000 a month.

• Gross burn: $220,000/month
• Net burn: $220,000 minus $70,000 = $150,000/month
• Runway: $1,200,000 divided by $150,000 = 8.0 months
• Cash-out date if nothing changes: eight months from the forecast date

That eight-month figure is a starting point, not an answer. It assumes revenue and spend both hold flat, which almost never happens. The next two sections cover the tests that turn a static runway number into a decision.

The default alive and default dead framework, first described by Paul Graham of Y Combinator, asks a sharper question than runway alone: given current growth in revenue and current growth in expenses, does the company reach profitability before it runs out of money, assuming no new funding? If yes, it is default alive. If no, it is default dead, regardless of how many months of runway sit in the bank today.

A company can have eighteen months of runway and still be default dead, if expenses are growing faster than revenue and the gap widens every quarter. A company can have five months of runway and be default alive, if revenue is compounding fast enough and expense growth has already been capped.

The test requires two trend lines, not two snapshots: monthly revenue growth rate and monthly expense growth rate, each measured over several months, extended forward at their current trajectory. If the extended lines cross into profitability before cash hits zero, the company does not need to raise again to survive, only to grow faster. If they do not cross, a new raise is not optional planning, it is the only path that avoids running out of cash, and that changes what the board should be reviewing every month.

This test is a planning tool, not an accounting standard, and it should sit alongside, not replace, the going-concern evaluation a company's auditor or accountant performs under US GAAP (see Sources). Default alive answers 'do we need to raise'; going concern answers a narrower legal and disclosure question about whether the financial statements can be prepared on the assumption the business continues operating for at least the next twelve months.

Runway and the default alive test both treat growth as a given input. The burn multiple asks whether that growth is being bought cheaply or expensively. It is calculated as net burn for a period divided by net new annual recurring revenue added in that same period. A company that burns $600,000 in a quarter while adding $500,000 in net new ARR has a burn multiple of 1.2x: it is spending $1.20 to buy $1.00 of new recurring revenue.

The metric was popularized by investor David Sacks in a widely cited framework built for recurring-revenue businesses (see Sources), and it travels well because it strips out absolute company size. A $2 million ARR company and a $40 million ARR company can be compared on the same 1.2x-style figure even though their dollar burn is wildly different.

As a bullet-row comparison of how the ratio is generally read, treat these as commonly cited rules of thumb rather than a fixed standard, since no regulator or accounting body sets them, and always confirm the current market read with your board or investors before using it in a deck:

• Burn multiple under 1x: revenue growth is outpacing burn, an efficient position at almost any stage.
• Burn multiple around 1x to 1.5x: generally read as a healthy, sustainable pace for a growing recurring-revenue business.
• Burn multiple around 1.5x to 3x: often still fundable, but worth a hard look at where the cash is going.
• Burn multiple above 3x: usually flagged by investors as a sign growth is being bought rather than earned, worth investigating before the next raise conversation.

The burn multiple only works cleanly for a company with real recurring revenue. A services business, a marketplace with lumpy take-rate revenue, or a hardware company with long sales cycles will get a distorted, less useful number from the same formula, because 'net new ARR' does not map cleanly onto what those businesses actually sell.

A single trailing-average burn number smooths over the exact week a company runs out of cash, because payroll, rent, and a vendor's 30-day terms rarely land evenly across a month. A 13-week rolling cash flow forecast, updated weekly against what actually cleared the bank, catches the week a $180,000 payroll run, a $40,000 quarterly insurance payment, and a $25,000 software renewal happen to land in the same seven days, even when the monthly average looks fine.

Building one starts with the actual bank balance today, then lays out every known cash inflow (collections by invoice due date, not by invoice issue date) and every known cash outflow (payroll dates, rent, loan payments, tax due dates, vendor terms) week by week for the next thirteen weeks. Anything uncertain gets a range, not a single guess: a sales pipeline deal closing 'sometime in weeks 6 to 9' should show up as a low case with it excluded and a high case with it included, not as a single blended number that hides the risk.

The forecast is only useful if it gets checked against reality every week. Compare last week's forecast to what actually cleared the bank, log the variance, and find out why it moved: a customer paid two weeks late, a vendor pulled payment forward, a hire started a pay period earlier than modeled. That weekly variance review is what turns the model from a one-time spreadsheet into an early warning system, and it is the document most lenders and investors will ask to see first when cash gets tight, because it shows the company already knows the tight week is coming rather than being surprised by it.

A single runway number answers 'how many months at today's rate.' Scenario planning answers the more useful question: 'what does the cash-out date look like under a plan we can actually execute against.' Build at minimum three named scenarios, each with its own cash-out date, not just a single sensitivity toggle.

• Base case: current trends continue, no new hires beyond ones already committed, revenue grows at the trailing average rate.
• Downside case: a named large customer churns, a planned raise slips by one quarter, or a seasonal revenue dip that has happened before happens again; hiring freezes the day the downside trigger is confirmed.
• Cash-preservation case: the plan the company would actually execute if the downside case starts to materialize: which specific hires get paused, which specific vendor contracts get renegotiated or cancelled, and by what date each action needs to be decided to matter before cash gets critical.

Each scenario should produce its own explicit cash-out date, and the gap between the base case date and the downside case date is the real number to manage against, not either date alone. A 45-day gap between the two means the company has 45 days of decision room once a downside signal appears. A 10-day gap means a downside signal has to trigger action the same week it is spotted, with no room to deliberate.

Revisit all three scenarios monthly, on the same day the board package goes out, using the actual trailing quarter's numbers rather than the assumptions the scenarios were built on six months earlier. A scenario plan built once at fundraise and never updated is a historical document, not a planning tool.

Runway extends two ways: raise more cash, or change the net burn number. Since a raise is not always available on a founder's timeline, the levers that change net burn are worth ranking by how quickly they show up in the bank balance.

• Fastest, days to weeks: collections speed. Moving payment terms shorter on new contracts, running a specific past-due accounts receivable list, and requiring a deposit before starting new work all pull cash forward without changing anything about the business itself.
• Weeks: a specific vendor or software renegotiation. Auditing every recurring software and vendor line for usage against seats or volume actually paid for, then cancelling or downsizing the unused portion, has a real and fast effect and does not touch headcount.
• One to two pay cycles: slowing or pausing planned hiring. Every open req not yet started costs nothing to freeze; every offer already accepted costs a full pay cycle's notice to unwind cleanly.
• One quarter or more: price increases on existing customers, which usually require a notice period and produce their full effect only after the next billing cycle for every customer, not immediately.
• Slowest and highest-risk if handled poorly: headcount reduction. It produces the largest single change to net burn but carries legal notice requirements, severance cost that reduces cash in the short term before it saves cash later, and morale effects on the team that stays; it should follow, not substitute for, the faster levers above.

The mistake most founders make under pressure is reaching for headcount first because it is the biggest number, before exhausting collections, vendor terms, and hiring freezes, which are faster, reversible, and carry none of the legal or morale cost of a reduction.

A board slide that shows a single runway number without its inputs invites the wrong question in the room: 'is that number right,' instead of the useful question, 'what should we do about it.' A clean board reporting page for burn and runway shows the trailing three-month trend for gross burn, net burn, and cash balance side by side, not just the current month's figures, so a director can see whether the trend is improving or deteriorating before asking.

Pair the trailing trend with the forward view: the current runway number stated with its calculation date, the default alive or default dead read for the quarter, and the base-case versus downside-case cash-out dates from the scenario plan. A board that sees the same four numbers in the same format every month, updated on the same cadence, can track a small deterioration early. A board that only sees a fresh narrative each quarter has no baseline to compare against and tends to find out about a problem only once it is acute.

When the news is genuinely bad, a specific ask beats a vague warning. 'Runway is down to four months, here are the three levers we are pulling and the dates each one lands' gives a board something to react to. 'Cash is getting tight' does not. Boards generally react worse to being surprised by a cash problem than to the problem itself, because a surprise implies management either did not see it coming or did not say so in time.

Finbryn's monthly finance review and board reporting pack is built around this same trailing-plus-forward format, using the company's actual bank and accounting data rather than a template filled in from memory.

A handful of recurring errors show up across founder-built runway models, almost always in the direction of making the number look better than the cash position actually supports.

• Counting a signed term sheet as cash. A term sheet is not a wire. Runway calculated as if a raise already in the bank has closed, before funds actually settle, has led more than one company to keep spending against money that arrived weeks late or fell through entirely.
• Using invoiced revenue instead of collected cash. An invoice sent is not cash received; a customer on 60-day terms who has not yet paid should not appear in this month's net burn calculation.
• Ignoring a line of credit's draw limits and covenants. Available credit is not the same as available cash if a covenant (a minimum cash balance, a debt service ratio) restricts when and how much can actually be drawn.
• Excluding one-time expenses because they are 'one-time.' A payroll tax true-up, an annual insurance renewal, or a lease deposit still leaves the bank account exactly like any other expense; excluding it from the average just moves the surprise to the month it actually hits.
• Treating restricted cash as unrestricted. A security deposit held by a landlord, funds in escrow tied to an acquisition, or a customer prepayment that must be refunded if the work is not delivered are not available to cover payroll.

Each of these errors is small individually but compounds: a runway model with two or three of them can overstate real runway by a month or more, which is exactly the margin that turns a manageable cash decision into an emergency one.

A founder tracking burn and runway on a spreadsheet updated occasionally is fine at the earliest stage, when the numbers are small and the founder is close to every transaction. Three signals usually mean it is time to bring in dedicated finance support rather than keep stretching a founder's own time across it.

The first signal is size: once monthly burn crosses roughly $100,000 to $150,000, the dollar cost of a modeling mistake, a missed collections week, or a forecast built on stale assumptions starts to matter more than the cost of paying someone to get it right. The second signal is complexity: multiple revenue streams, a mix of monthly and annual contracts, or a payroll that spans contractors and full-time staff across more than one entity all make a spreadsheet-based model error-prone in ways that compound month over month. The third signal is audience: once a board, a lender, or a prospective investor is asking for a rolling forecast and a monthly variance review as a standing deliverable, not an occasional favor, the reporting itself has become a job.

A fractional CFO engagement typically starts with a 13-week cash flow forecast and a monthly finance review, building outward into scenario planning and board reporting once the baseline model is solid. If the company's financial statements are being prepared under US GAAP and cash is genuinely tight, ask whoever prepares or reviews those statements whether a going-concern disclosure applies under the FASB's evaluation standard; that is a distinct question from the internal default alive test covered earlier, and it is not one to guess at without a credentialed preparer or reviewer involved.

Finbryn's virtual CFO and 13-week cash flow forecast services are built for exactly this handoff point: a company that has outgrown a founder-maintained spreadsheet but is not yet ready for a full-time finance hire.