Ask a founder how much runway they have and you will usually get a number that is wrong in the same direction: too optimistic. Not because anyone is being dishonest, but because the standard calculation — cash divided by average monthly burn — quietly assumes that the last three months predict the next twelve. They almost never do.
Runway is the number that determines when you raise, whether you hire, and how much leverage you have in every negotiation you enter. It is worth calculating correctly.
Gross burn versus net burn
Gross burn is total monthly cash operating expenses. Everything that leaves the bank to run the business — payroll, rent, software, contractors, marketing, insurance. It ignores revenue entirely.
Net burn is gross burn minus cash collected from customers. It is the actual monthly decline in your cash balance.
Both matter, and they answer different questions. Net burn tells you how fast the tank is draining. Gross burn tells you what your obligations are if revenue disappears — which is exactly the question that matters when a large customer churns, a payment cycle slips, or a market turns. A company with $400K gross burn and $80K net burn looks efficient right up until it loses the customer generating $320K a month in collections. Then it is a $400K burn company with whatever cash it has left.
Investors ask for net burn. Track both, and know how quickly net burn converges toward gross burn if your largest one or two revenue sources go away.
Note that both should be measured in cash, not accrual expense. If you booked a $60,000 annual insurance premium as $5,000 per month on the P&L but wrote the check in January, your January burn was $60,000. Burn is a cash concept. Pull it from the bank, not the income statement.
The formula, and the four ways it lies
Runway (months) = Cash on hand ÷ Net monthly burn
The formula is arithmetically fine. The inputs are where it breaks.
- Non-recurring items contaminate the burn average. If your trailing three-month average includes a one-time legal settlement, an annual insurance renewal, a conference, or a piece of equipment, your burn rate is overstated and your runway is better than you think. If those months happened to be clean — no quarterly tax payment, no annual renewals, no true-ups — your burn is understated and your runway is worse. Normalize: strip out non-recurring items, then add back an accrued monthly allowance for the lumpy costs you know are coming.
- Committed spend is invisible in a trailing average. A signed lease, a multi-year software contract, a severance agreement, a term loan amortization schedule — these are obligations regardless of what you do next. If you calculate runway from average burn and then plan to cut, you need to know which portion of that burn you cannot actually cut. For most companies, 60 to 80% of the expense base is committed or effectively fixed over a 90-day horizon.
- Deferred revenue in the cash balance is already spent. If you collect annual subscriptions upfront, some portion of your bank balance is money you owe in future service delivery. It funds the business — that is the point — but it is not the same as unencumbered cash, and if you are modeling a wind-down or a distressed sale, it is not yours. Subtract it to get a conservative floor on your real position.
- Step-function costs break the linear assumption. Runway math assumes a flat burn line. Real burn moves in steps: a hire lands and burn jumps $15K a month permanently. A lease starts. A contract renews at a higher tier. A tax payment comes due. If your hiring plan adds four people over the next two quarters, your burn in month 6 is not your burn today, and a flat calculation will overstate your runway by months.
The correct approach is not a single division. It is a month-by-month cash model that carries forward the actual expected burn for each period — which is what the 13-week forecast does over a quarter, extended out over the fundraising horizon.
Default alive or default dead
Paul Graham’s framing is the most useful single question in this area: on your current growth trajectory and current expense plan, do you reach profitability before you run out of money?
If yes, you are default alive. If no, you are default dead.
Most early-stage companies are default dead, and that is a normal condition rather than a crisis — it is what raising capital is for. The failure is not being default dead. The failure is being default dead and not knowing it, because that founder is negotiating from a position they have misread.
Two things make the answer non-obvious. First, the trajectory has to be real: current growth rate applied forward, not the plan. Second, the expense line has to include the hires already committed. A company that is default alive on paper and has four signed offers starting next month may not be.
Run the number honestly, then re-run it under the assumption that growth slows by half. If you are still default alive, you have genuine optionality — you can raise on your terms or not raise at all. That is the strongest position available to a founder, and it is worth a great deal in a negotiation.
Extending runway, ranked by speed and reversibility
The order matters. Start with the levers that produce cash fastest and do the least permanent damage.
- Accelerate collections. The fastest cash available to most companies is already earned and sitting in accounts receivable. Work the aging report by name. Call, do not email. Offer a 1–2% discount for immediate payment on large balances — expensive as annualized financing, cheap compared to dilution. Tighten terms on new contracts, require deposits, and invoice the day work is delivered rather than at month end. A company with a 55-day DSO that gets to 40 frees roughly two weeks of revenue in one-time cash. This is fully reversible and costs you nothing structural.
- Renegotiate vendor terms. Move payables from net 30 to net 45 or net 60. Convert annual prepayments to quarterly or monthly — you will often pay a small premium, which is worth it when cash is the constraint. Ask software vendors for a payment plan rather than a discount; they are usually more flexible on timing than on price. Do this before you are distressed, while you still look like a customer worth accommodating.
- Cut discretionary spend. Unused software seats, redundant tools, travel, events, agency retainers on month-to-month terms, marketing spend that is not producing measurable pipeline. Audit every recurring charge on the bank and card statements. Most companies find 10 to 15% of non-payroll spend they cannot justify. Fast, mostly reversible, and it costs you very little.
- Consolidate contractors and vendors. Contractor and agency spend is often the largest cuttable line after payroll, and it is far easier to unwind than employment. Cancel or scope down what is not on the critical path. Bring work in-house where you have capacity. Reversible with some friction.
- Reduce headcount. Last, because it is the slowest to produce net savings and the hardest to undo. Severance, accrued PTO payout, and unemployment insurance costs mean a reduction often costs cash in month one and does not turn cash-positive until month two or three. It damages morale and institutional knowledge, and rehiring is expensive and slow.
If you do it, do it once and cut deep enough that you do not have to return. Serial small reductions are worse for the organization than one decisive action, and they signal to everyone remaining that more are coming.
Two things that look like runway extension and usually are not: venture debt, which converts a cash problem into a covenant problem and typically requires a recent equity round to access; and deferring payroll taxes, which is not a financing option — it creates personal liability for officers and is one of the few debts that survives bankruptcy.
The 18-month rule, and why you start at 12
The convention is to raise enough for 18 to 24 months. The reason is not arbitrary: you need roughly 6 months to run a process, and you need 12 months after closing to build the traction that justifies the next round’s valuation. Less than 18 and you are back in market before you have new results to show.
Which means the number that matters is not when your cash runs out — it is when you start the raise. A process from first conversation to money in the bank runs 3 to 6 months in a good market and longer in a bad one. Start at 12 months of runway, not 6.
Founders who start at 6 months are visibly constrained, and investors price that. Diligence stretches, terms harden, and the bridge conversation replaces the round conversation. The same company with the same metrics raising from 12 months out has the ability to walk away, which is the only real leverage in the negotiation.
Build the calendar backward from your zero-cash date. Subtract three months of operating buffer, subtract five months of process, and that is your start date. Note it, and do not let it pass because the quarter looks busy.
The relationship between the three numbers
Burn rate, runway, and cash forecast are one system. The 13-week forecast tells you whether you can meet obligations this quarter. Burn rate tells you the rate at which the position is deteriorating. Runway converts that rate into a date, and the date determines when you raise, hire, or cut.
Where founders get into trouble is calculating the third without the first two — dividing a bank balance by a rough monthly number, getting an answer that feels comfortable, and building a plan on it. The arithmetic is easy. Getting the inputs right is the work.
Pegacorn Group provides fractional CFO and back-office support to venture-backed startups, nonprofits, and public companies. If you want a runway number you can put in front of a board, we can help you build it.