Reading burn rate and runway like a biotech CFO

The two numbers that govern a pre-revenue company

Burn rateBurn rateBurn rate is the speed at which a company spends its cash reserves, usually measured per month, before reaching profitability or raising more funding.Voir la définition complète → is how much cash the company consumes each month. Runway is how many months of cash remain before the tank hits empty.

The formula is simple:

The judgment is not simple. Where you draw the line on "burn," which cash you count, and how lumpy the spending is: that is where biotech diverges hard from software.

Walking a Series A gene-therapy cash flow statement

Imagine a Series A gene-therapy company. (Numbers below are illustrative, not a real company.) It just closed a $60 million round. Its most recent quarter looks like this:

| Line item | Quarterly cash flow |

|---|---|

| Cash from operations | -$9.0M |

| R&D spend (inside operations) | -$6.5M |

| G&A spend (inside operations) | -$2.5M |

| Capital expenditureCapital expenditureCapital Expenditure (CapEx) is money spent to acquire, upgrade, or extend long-lived assets like equipment, property, or software that deliver value over multiple years.Voir la définition complète → (lab buildout) | -$4.0M |

| Cash from financing | +$60.0M |

Two burn definitions matter here.

Gross burnGross burnBurn rate is the speed at which a company spends its cash reserves, usually measured per month, before reaching profitability or raising more funding.Voir la définition complète → is total cash going out the door: about $15 million this quarter ($9M operating plus $4M capexcapexCapital Expenditure (CapEx) is money spent to acquire, upgrade, or extend long-lived assets like equipment, property, or software that deliver value over multiple years.Voir la définition complète →, since revenue is zero).

Net burnNet burnBurn rate is the speed at which a company spends its cash reserves, usually measured per month, before reaching profitability or raising more funding.Voir la définition complète → subtracts any cash coming in from operations (product sales, grants, milestone payments). This company has no product revenue, so gross and net operating burn are close. But suppose it received a $1 million research grant. Net operating burn would drop to $8 million for the quarter.

Monthly net operating burn: roughly $3 million ($9M / 3 months).

Now calculate runway

Post-raise cash on hand: assume $65 million.

But wait. That $4 million lab buildout was a one-time capital expensecapital expenseCapital Expenditure (CapEx) is money spent to acquire, upgrade, or extend long-lived assets like equipment, property, or software that deliver value over multiple years.Voir la définition complète →, not a recurring monthly cost. A sloppy analyst folds capexcapexCapital Expenditure (CapEx) is money spent to acquire, upgrade, or extend long-lived assets like equipment, property, or software that deliver value over multiple years.Voir la définition complète → into monthly burn and understates runway. A sharp CFO separates recurring operating burn from one-time capital projects, then models when the next lumpy expense hits.

That distinction (recurring versus lumpy) is the whole game in biotech.

Why R&D burn behaves differently from SaaS burn

In SaaS, burn scales somewhat smoothly. You hire reps, spend on cloud infrastructure, and watch revenue climb in step. Burn and growth move together.

Biotech burn is step-function and milestone-driven. It jumps in discrete blocks tied to the drug development timeline, not to revenue (because there usually is no revenue for years).

Here is the sequence that drives the steps:

• Preclinical work: lab research and animal studies before human testing.
• IND filing: an Investigational New Drug application, the request to the FDA (Food and Drug Administration, the US drug regulator) for permission to test in humans.
• Phase 1, 2, 3 clinical trials: progressively larger human studies. Each phase costs dramatically more than the last.

A gene-therapy company faces an extra burn driver most biotechs share: manufacturing. Producing viral vectors (the modified viruses used to deliver the corrected gene) is extraordinarily expensive and often requires building or contracting specialized facilities. That $4 million lab buildout above? For gene therapy, process development and manufacturing can dwarf the actual clinical trial cost in early stages.

The step-function in practice

Watch what happens to monthly burn as this company advances:

| Stage | Approx. monthly operating burn |

|---|---|

| Preclinical (today) | $3M |

| IND-enabling studies | $4M to $5M |

| Phase 1 start | $6M+ |

| Manufacturing scale-up | can spike sharply |

Burn does not creep. It leaps when the company hits a new stage. So a CFO never says "we have 21 months of runway" and stops there. The real question is: 21 months at which burn rate?

Runway is really about the next value inflection

Here is the mental model biotech CFOs use that SaaS CFOs mostly do not.

Cash is not raised to "reachreachThe number of unique people exposed to your message in a given period. Unlike impressions, reach counts each person once, no matter how often they see it.Voir la définition complète → profitability." It is raised to reachreachThe number of unique people exposed to your message in a given period. Unlike impressions, reach counts each person once, no matter how often they see it.Voir la définition complète → the next data readout: the trial result or regulatory milestone that increases the company's value and lets it raise the next round at a higher price.

So runway gets measured against catalysts, not just calendar months. The CFO asks:

> Does our cash get us past the Phase 1 readout, with a few months of buffer to negotiate the Series B from a position of strength?

If the Phase 1 readout lands at month 18 and runway is 21 months, that is tight but workable. If the readout slips to month 22, the company is raising money with an empty tank and no fresh data, which is the worst possible negotiating table.

For a grounding in how these development phases and their costs are structured, the FDA's overview of the drug development process is a solid, free primer.

Building a runway model a CFO would trust

A credible model layers the step-function into a month-by-month cash forecast. Roughly:

1. Start with cash on hand (post-raise, verified against the bank, not the pitch deck).

2. Map recurring operating burn by stage, not as one flat number.

3. Add lumpy items on their real dates: manufacturing runs, capexcapexCapital Expenditure (CapEx) is money spent to acquire, upgrade, or extend long-lived assets like equipment, property, or software that deliver value over multiple years.Voir la définition complète →, IND fees, milestone payments to research partners.

4. Subtract expected inflows conservatively: grants and partnership payments only when contractually likely.

5. Find the month cash crosses zero. That is your true runway, and it is almost always shorter than the naive "cash divided by current burn" figure suggests, because burn rises.

Then apply the CFO's rule of thumb: raise the next round with 6 to 12 months of runway still on the clock. Fundraising takes months, and biotech markets swing. Running to near-zero forces bad terms or a down round (raising at a lower valuation than the prior round), which punishes existing shareholders.

Reading the signals in someone else's numbers

If you are evaluating a biotech (as an investor, partner, or job candidate), the cash flow statement tells you more than the press release.

Look for the gap between cash and catalyst. Public biotechs disclose cash position and often guide on how many quarters it funds. If a company says cash funds operations "into Q4 2027" but the pivotal readout is expected in 2028, that gap is a flashing light. Expect a raise, a partnership, or a pipelinepipelineAll active sales opportunities across the stages of the sales process, together with their combined potential value and probability of closing.Voir la définition complète → cut.

Distinguish burn that buys data from burn that buys overhead. A high R&D-to-G&A ratio generally signals capital going toward value-creating experiments. Bloated G&A on a pre-revenue company is a warning.

Watch manufacturing commitments. For gene and cell therapy especially, a signed manufacturing contract can lock in large future cash outflows that are not obvious from a single quarter's statement. Read the footnotes.

Treat guidance as an estimate. Trials slip. A company's own runway guidance assumes trials stay on schedule, which they frequently do not. Build in a buffer when you model it yourself.

A quick sanity check you can run in 60 seconds

Given any biotech's recent filing:

• Grab cash and equivalents from the balance sheet.
• Grab cash used in operating activities for the last quarter, and multiply by 4 for a rough annual burn (or divide the quarter by 3 for monthly).
• Divide. That is your first-pass runway.
• Then ask the two biotech-specific questions: Is burn about to step up? and Does this reach the next data catalyst with buffer?

That last pair is what separates reading the number from reading the company.

Key Takeaways

• Runway equals cash divided by net burn, but the honest version models burn as a rising step-function, not a flat monthly figure. Separate recurring operating burn from one-time capexcapexCapital Expenditure (CapEx) is money spent to acquire, upgrade, or extend long-lived assets like equipment, property, or software that deliver value over multiple years.Voir la définition complète → and lumpy manufacturing spend.
• Biotech burn is milestone-driven, not revenue-driven. Cash is raised to reachreachThe number of unique people exposed to your message in a given period. Unlike impressions, reach counts each person once, no matter how often they see it.Voir la définition complète → the next data readout, so measure runway against catalysts, not just the calendar.
• Gene and cell therapy add a manufacturing burn driver (viral vector production, specialized facilities) that can dominate early-stage costs. Always read the footnotes for locked-in commitments.