Burn Rate and Runway Explained: How to Calculate How Long Your Startup’s Cash Will Last

Every startup founder eventually asks the same question, usually at 2 a.m.: how long can we keep going at this pace before the money runs out? Burn rate and runway are the two numbers that answer it. Burn rate is how fast your company spends cash each month. Runway is how many months that pace leaves you. Together they are the only financial question that is existential for a pre-profit startup, because a company with a great product and no cash still closes.

The good news is that both numbers come from simple arithmetic. The hard part is getting honest inputs — and knowing which version of each number to trust.

What Is Burn Rate?

Burn rate is the pace at which your company consumes cash, measured monthly. If your bank balance drops from $800,000 to $750,000 over a month with no fundraise in between, you burned $50,000 that month. That is the whole idea. Everything else is about making sure the number you calculate actually reflects reality.

There are two kinds of burn rate, and confusing them is the most common mistake founders make.

Gross burn is total cash out the door each month — payroll, rent, software, hosting, marketing, contractors, everything — ignoring any cash coming in.If a company spends $300,000 on salaries, $50,000 on software and infrastructure, $30,000 on office costs and $20,000 on marketing in a given month, its gross burn rate is $400,000 per month.

Net burn is cash out minus cash in. It answers the question that actually matters: how fast is the bank balance really declining? If that same company collected $150,000 in revenue during the month, its net burn rate is $250,000 per month.

The formulas:

• Gross burn = total monthly cash operating outflow
• Net burn = monthly cash outflows − monthly cash inflows

For a pre-revenue startup, gross and net burn are identical — there is no revenue to subtract. For a revenue-generating startup, net burn is the figure that matters, because it reflects the real drain on reserves. Gross burn still matters for cost control: it sizes your cost structure. But only net burn belongs in the runway calculation.

One more distinction that trips people up: burn rate is a cash measure, not an accounting one. It ignores non-cash charges like depreciation and stock-based compensation entirely, and it ignores revenue you have earned but have not collected. If your books are on an accrual basis — and if you are a SaaS company past your seed round, they should be — your income statement records revenue when it is earned and expenses when they are incurred, not when cash moves. In that case the honest way to get burn from the books is: net loss, plus non-cash expenses, adjusted for changes in working capital. The simplest cross-check is always the bank balance: the month-over-month change in cash, excluding financing inflows, is your true burn.

What Is Runway, and How Do You Calculate It?

Runway is your cash balance divided by your monthly burn — the number of months until the balance hits zero if nothing changes.

Runway (months) = cash balance ÷ monthly net burn

A startup with $1.5 million in the bank burning $150,000 a month has 10 months of runway. A startup with $2.4 million and a $240,000 monthly net burn also has 10 months. The equation rearranges three ways, and all three are useful in planning: runway = cash ÷ net burn; net burn = cash ÷ runway; and cash needed for N months = net burn × N.

Two adjustments make the calculation honest instead of flattering.

First, use net cash, not the raw bank balance. Subtract drawn credit lines, credit card balances and other near-term obligations from cash on hand. $625,000 in the bank with $25,000 on cards is $600,000 of net cash. Count all available liquidity — operating accounts, money market accounts, short-term investments and any committed-but-undisbursed funding — but do not count money you merely hope to raise.

Second, use a trailing three-month average for the burn in the denominator, not a single month. One month is a noisy input. Legal fees, annual insurance premiums, a laptop refresh, a conference — one-off items distort any single month in either direction. Averaging three months smooths the invoice calendar out of the number. Some well-run startups also track a rolling 13-week cash flow alongside the monthly burn figure, because the 13-week view catches short-term cash gaps that a monthly average can hide.

There is also a distinction worth knowing when you talk to investors: cash runway is the pure calculation, while funded runway extends it with committed future funding. Keep the two separate in your own head, and be clear about which one you are quoting.

A Worked Example

Take a small SaaS startup, three months after its seed round:

• Cash on hand: $900,000
• Credit card balance: $15,000
• Monthly cash outflows (3-month average): $130,000
• Monthly cash collected from customers (3-month average): $45,000

Net cash is $900,000 − $15,000 = $885,000. Net burn is $130,000 − $45,000 = $85,000 per month. Runway is $885,000 ÷ $85,000 = 10.4 months.

That is the headline number. But the honest version goes further. The forecast says a senior hire starts next month, adding $14,000 a month, and the annual insurance premium of $24,000 lands in month four. Recomputing with those known changes, the real runway is closer to 9 months — and the founder now knows the fundraising clock starts in about three months, not four. A runway number built from a forecast, including the things that fall outside a typical month, is worth acting on. One built from last month alone is a snapshot that assumes the future looks exactly like the past month, which it never does.

How Many Months of Runway Should a Startup Have?

There is no universal safe number, but there are well-established benchmarks. Twelve to 18 months after closing a round is the working standard most founders and investors use. J.P. Morgan’s runway guidance describes 18 to 24 months as the historical guideline and notes that 24 to 36 months is more frequently recommended in tighter funding markets. The logic is simple: a fundraise takes three to six months from first meeting to money in the bank, and you want to start it from strength, not desperation.

A useful way to think about the bands:

• 18+ months: Comfortable. Ample time to hit milestones and fundraise without pressure. Begin next-round conversations when about 12 months remain.
• 12–18 months: Healthy, but the clock is real. Start fundraising preparation when 9–12 months remain.
• 6–12 months: Urgent. Fundraising or a burn cut should already be under way.
• Under 6 months: Critical. This is the zone where options narrow fast — bridge rounds, cuts, or a sale become the conversation.

The stakes are not theoretical. CB Insights reviewed 431 VC-backed startup shutdowns since 2023 in a March 2026 report, and running out of cash — often after a runway that looked longer on paper than it was — remains one of the recurring causes. Paul Graham’s 2015 essay “Default Alive or Default Dead?” frames the same idea as a question every founder should be able to answer: if nothing changes, does the company reach profitability before the money runs out, or does it die first? Runway is the number that answers it.

What Is a Good Burn Rate?

Burn rate is not automatically good or bad. A higher burn can be reasonable if it funds validated growth with enough runway behind it, and a low burn can be a problem if it means the company is not investing in the growth it needs. What matters is efficiency, and the metric investors use for that is the burn multiple.

Burn multiple = net burn ÷ net new revenue over a period

A burn multiple of 1 means the company spends $1 to add $1 of new revenue. Under 1 is efficient; 2–3 is common for early-stage companies investing ahead of revenue; above 3 deserves a hard look at whether the spending is actually producing growth. Track the multiple alongside the burn itself, because a rising burn with a falling multiple is a very different story from a rising burn with a rising one.

The Mistakes That Make Runway Look Longer Than It Is

Most runway surprises come from the same short list. Check your own numbers against it.

Counting gross burn as net burn. If you have revenue and you divide cash by gross burn, you understate your runway — the safe direction, but it can push you into an unnecessary fundraise. The dangerous version is the reverse: quoting a runway based on a single good month of collections.

Using one month’s burn. A month with no payroll tax payment or no annual renewals looks cheap. Three-month trailing average, always.

Forgetting committed spending. Hires already agreed, a lease starting next quarter, a big purchase planned — if it is committed, it belongs in the forecast version of the number.

Counting restricted cash. Under accounting standard ASU 2016-18, restricted cash sits with cash and cash equivalents in the cash flow statement while being presented separately on the balance sheet. Money you cannot spend is not runway.

Treating runway as a countdown instead of a plan. Runway does not tell you what to do; it tells you how much time you have to decide. The founders who use it well set trigger points in advance: at 12 months remaining we start the fundraise; at 9 months we cut discretionary spend by 20%; at 6 months we make the hard call. Decide the triggers while you still have options, not after they have closed.

How to Reduce Burn Rate Without Cutting What Drives Growth

When the number comes back shorter than you want, the instinct is to cut everything. That usually backfires. Start with the spending that does not produce growth or learning: duplicate SaaS tools, unused seats, contractor spend on work nobody uses, office space you do not fill. Then look at timing rather than size — a hire delayed by a quarter extends runway by the same amount as a small cut, without losing the person.

Renegotiate before you cancel. Annual billing on tools you actually use is often 15–20% cheaper than monthly. Vendors will frequently extend terms for a startup that asks. And look at revenue timing too: annual prepay discounts, collected faster, reduce net burn just as surely as a cost cut does, and they do it without touching the team.

If you do have to cut people, do it once and clearly rather than in a series of small rounds. Repeated cuts destroy morale and signal to the team — and to investors — that leadership does not have a plan. One decisive cut, explained honestly, preserves trust.

How Often Should You Calculate Burn Rate and Runway?

Monthly, at minimum. Many well-run startups review it weekly during a fundraise or a cash crunch, and the best-run ones keep a rolling forecast that updates as new information arrives: a signed contract, a lost customer, a hire, a price change. The calculation takes ten minutes once the inputs are clean. The discipline is not the arithmetic — it is keeping the inputs honest and looking at the number before it becomes an emergency.

If you take one thing from this guide, take this: runway is cash divided by net burn, averaged over three months, using net cash, with known future changes included. Everything else is commentary. And if your runway looks shorter than you expected, that is exactly what the calculation is for — it is why your runway can look shorter than the calculator says, and the earlier you see it, the more options you still have.