The median time from seed to Series A now stretches past two years, according to Crunchbase funding data, yet most founders still calculate runway with a formula that assumes burn never changes. Cash divided by last month's burn gives you a single static number. Your actual runway is a moving target that shifts with every hire, every renewal, and every annual contract that does or does not land.

This page is a complete runway calculator you can work through in about five minutes. It covers the basic formula, the forward-burn adjustment that makes the number trustworthy, a lookup table for quick answers, and the benchmarks VCs use to judge whether your runway is fundable. Across roughly 100 venture-backed clients, the pattern we see most often is not that founders lack a runway number. It is that the number they present to their board is 2 to 4 months more optimistic than reality.

The Basic Runway Formula

Runway in months equals cash on hand divided by monthly net burn:

Runway = Total Cash ÷ Monthly Net Burn

Two definitions matter here:

• Gross burn is total monthly cash outflow: payroll, rent, software, contractors, cloud costs, everything that leaves the bank.
• Net burn is gross burn minus cash collected from customers. This is the number that determines runway.

If you spend $400K a month and collect $150K from customers, your net burn is $250K. With $5M in the bank, your naive runway is 20 months.

That naive number is where most founders stop. It is also where most runway errors begin.

Quick Lookup: Runway by Cash and Burn

Find your cash position across the top and your monthly net burn down the side. The result is your naive runway in months.

Use this table for a gut check, then run the five-step calculation below to get a number you can actually plan against.

The Five-Step Runway Calculation That Holds Up

Static runway assumes tomorrow looks like last month. It never does. Here is the calculation we run for clients, and that you can run yourself in a spreadsheet in one sitting.

Step 1: Establish true cash. Start with bank balances, then subtract anything that is not really yours to spend: security deposits, credit card holds, payroll that has accrued but not yet hit the account, and any debt principal due inside your planning window. If you hold customer prepayments for services not yet delivered, flag them. The cash is real but the obligation behind it is too.

Step 2: Use a 3-month average net burn, not last month. Any single month is noisy. Annual software renewals, three-payroll months, bonus payouts, and one-time legal fees all distort it. Average your last three months of net burn. If one month contains a large one-time item, note it and consider excluding it.

Step 3: Layer in committed future changes. This is the step that separates a real runway number from a naive one. Add the fully loaded cost of every signed offer that has not started. Add known price increases on cloud and software contracts. Subtract expenses that are genuinely ending. A startup with $300K average burn and four signed offers at $20K a month fully loaded is really running at $380K within a quarter. On $6M of cash, that is the difference between 20 months of runway and 16.

Step 4: Haircut projected collections. Founders consistently overestimate near-term revenue. If your runway math depends on pipeline closing, apply your actual historical win rate, not the forecast in your CRM. A conservative approach: count only signed contracts and renewals with high logo retention. Benchmarks from SaaS Capital's research show revenue retention varies widely by ARR band, so use your own cohort data rather than an industry average when you have it.

Step 5: Recompute monthly. Runway is a metric with a shelf life of about 30 days. Our team pushes updated runway and variance-to-plan into client Slack channels in real time because a stale runway number is how startups end up "surprised" by a cash crunch that was visible two quarters earlier. If you are doing this manually, put a recurring monthly calendar block on it and treat it like payroll: non-negotiable.

For a more rigorous weekly view, pair this with a 13-week cash flow forecast, which catches timing risks that a monthly runway number smooths over.

Worked Example: Series A SaaS at $3M ARR

Five months of difference. That gap decides whether you start your next raise in March or in August, and whether you raise from a position of strength or desperation.

How Much Runway Do You Actually Need?

The answer depends on stage, and the bar has moved. When rounds closed in 8 weeks, 18 months of runway was comfortable. With fundraising timelines stretched, the working standard has shifted up.

Two principles sit underneath these numbers.

First, Paul Graham's default alive test: at your current growth rate and burn, do you reach profitability before you run out of money? If yes, you are default alive and fundraising is a choice. If no, you are default dead and fundraising is a deadline. Every board should know which one they are looking at.

Second, start raising with at least 9 to 12 months of runway remaining. A raise takes 3 to 6 months of calendar time in a normal market. If you start with 6 months left, every investor you meet can smell it, and the term sheet reflects it. Our clients have raised roughly $800M in aggregate, and the single most reliable predictor of a clean process is starting it early with a credible model behind it.

Runway Is Necessary but Not Sufficient: Enter Burn Multiple

Investors no longer evaluate runway in isolation. They ask what you are converting that burn into. Burn multiple, popularized by David Sacks and now tracked in the Bessemer Venture Partners Atlas, is net burn divided by net new ARR. Burn $4M to add $2M of net new ARR and your burn multiple is 2.0x.

A startup with 30 months of runway and a 4x burn multiple is not "safe." It is slowly converting a strong balance sheet into a weak story. Meanwhile a startup with 16 months of runway and a 1.2x burn multiple can usually raise whenever it wants. Efficiency data from the KeyBanc and Sapphire Ventures SaaS survey consistently shows capital efficiency separating the companies that clear the Series B bar from those that stall. We published stage-specific targets in our 2026 burn multiple benchmarks for Series A SaaS if you want to see where you stand.

The practical takeaway: calculate runway to know your deadline, and calculate burn multiple to know whether the market will care when you hit it.

Three Scenarios Every Founder Should Model

One runway number is a snapshot. Three scenarios are a plan. Build these side by side in your model:

1. Base case. Current burn trajectory, committed hires, revenue at your historical attainment rate. This is your real runway.
2. Downside case. Revenue 30 percent under plan, one key renewal lost, no new financing. If runway in this case drops under 12 months, you need a pre-agreed trigger for cuts, and you need it in writing before the emotion of the moment.
3. Investment case. What happens if you add the two hires you are debating? If the incremental burn shortens runway past your fundraise start date, the hire is not a hiring decision. It is a financing decision.

The discipline here is not the spreadsheet. It is agreeing with your board, in advance, which scenario you are living in and what evidence would move you between them. Frameworks for structuring these growth-versus-burn tradeoffs are covered well in David Skok's SaaS metrics guide, and our free SaaS financial model template has the scenario toggles pre-built.

The Five Most Common Runway Calculation Mistakes

1. Using last month's burn. One quiet month makes you look healthier than you are. Use a 3-month average adjusted for one-timers.
2. Counting ARR as cash. A $600K annual contract billed monthly delivers $50K a month. Booking momentum is not collections. Bill annually upfront where you can; the runway impact is enormous.
3. Ignoring payroll timing. Committed offers with future start dates are real burn. So are severance obligations if you are planning cuts.
4. Treating prepaid annual contracts as free money. Cash from a prepaid annual deal extends runway today but creates a renewal cliff in 12 months. Model the cliff.
5. Calculating it once a quarter. Runway decays daily. A number computed in January and quoted in April is fiction. This is the reason we built a proprietary data pipeline that connects billing, banking, and HRIS systems and pushes live runway into Slack, because the alternative at most startups is a stale spreadsheet nobody trusts. Y Combinator's advice to founders in the YC Library hits the same theme repeatedly: know your numbers cold, especially cash.

If your finance stack cannot produce a trustworthy runway number inside a day, the problem is usually upstream systems, not the formula. That is a fixable engineering problem, and fixing it at the source beats re-reporting bad data every month.

When Runway Math Says You Need Help

There is a predictable moment when runway stops being a formula and becomes a full-time job: multiple revenue streams, 20+ employees, a board that wants scenarios instead of snapshots, and a raise on the horizon. If you are approaching that point, our guide on when to hire a fractional CFO walks through the specific triggers, and our Series A SaaS benchmarks guide shows the full metric set investors will expect alongside your runway number.

If you want the runway, burn multiple, and scenario work handled by a team that starts with a strategic plan rather than a spreadsheet, work with a fractional CFO at CFO Advisors. We are the preferred fractional CFO firm of several tier-1 VCs, the only one with an in-house engineering team, and our clients get board-grade runway reporting pushed to Slack in real time instead of six weeks after month-end.

FAQ

How do I calculate my startup's runway?

Divide total cash on hand by your monthly net burn (gross spending minus customer collections). For a reliable number, use a 3-month average of net burn, add the cost of signed-but-not-started hires, subtract accrued obligations like payroll and debt payments from cash, and haircut any projected collections to your historical attainment rate. Recompute monthly.

What is the difference between gross burn and net burn?

Gross burn is your total monthly cash outflow: payroll, rent, software, cloud, contractors, everything. Net burn subtracts cash collected from customers. Runway is always calculated on net burn. A company spending $500K and collecting $300K has $500K gross burn but only $200K net burn.

How many months of runway should a startup have?

Target 24 or more months after closing a round at seed and Series A, and 24 to 36 months at Series B. Begin your next raise with at least 9 to 12 months remaining, because a normal fundraise takes 3 to 6 months and negotiating leverage collapses when investors know you are nearly out of cash.

Does deferred revenue count toward runway?

The cash from prepaid contracts counts, since it is in your bank account and spendable. But it carries a delivery obligation and a renewal cliff. Best practice is to include the cash in runway while modeling the renewal date explicitly in your downside scenario, so a churned prepaid customer does not blindside you twice: once in ARR and again in collections.

Is 12 months of runway enough?

Twelve months is the floor at which you should already be in an active fundraise or executing a plan to reach default alive. It is not enough to operate comfortably: after a 3 to 6 month raise process, a 12-month position leaves you closing with 6 to 9 months left, which reads as desperation in a term sheet negotiation.

How often should I recalculate runway?

Monthly at minimum, weekly during a fundraise or a cash crunch. Burn shifts with every hire, renewal, and annual contract. High-performing finance teams automate this so runway updates continuously from live banking and billing data rather than waiting for the month-end close.

Sources

1. Crunchbase - Startup funding data and round timing
2. Paul Graham - Default Alive or Default Dead
3. SaaS Capital - SaaS retention and growth research
4. Bessemer Venture Partners Atlas - Efficiency metrics and burn multiple
5. KeyBanc Capital Markets and Sapphire Ventures - Annual SaaS Survey
6. David Skok, For Entrepreneurs - SaaS Metrics 2.0
7. Y Combinator Library - Founder guidance on metrics and cash management