For a clinical-stage biotech with no product revenue, one number governs almost everything: how long can it keep the lights on before it has to raise more money? That number is cash runway, and it is fully computable from a company's SEC filings. Runway is not a proprietary metric or an analyst's guess — it is arithmetic on two figures the company is required to disclose: how much liquid cash it holds, and how fast it is spending it.

The formula is simple: runway = liquid resources ÷ cash burn per period. The work is in sourcing the two inputs correctly from the filing. The numerator is the company's liquid resources: cash, cash equivalents, and short-term marketable securities (and sometimes short-term investments), taken from the balance sheet. The denominator is cash burn: the net cash the company consumes per quarter or per year, taken from the statement of cash flows — specifically net cash used in operating activities, often adjusted to reflect capital expenditures and other recurring uses. A real, SEC-filed disclosure shows the numerator and the company's own runway statement side by side.

"Cash, cash equivalents, and marketable securities totaled $398.2 million as of March 31, 2025. Septerna expects the upfront payment from the collaboration with Novo Nordisk to significantly extend its prior cash runway guidance of early 2028."— Septerna, Inc., Form 8-K Exhibit 99.1 (filed with the SEC), source

This single disclosure illustrates every moving part of a runway calculation. The numerator is explicit — $398.2 million in cash, cash equivalents, and marketable securities as of a stated date. The company also gives its own runway estimate ("prior cash runway guidance of early 2028"), which is the output of management running the same calculation with its internal burn assumptions. And it flags the single biggest reason a runway estimate changes: an inflow of cash. The upfront payment from the collaboration is new money in the numerator, which is why management says it expects the upfront to "significantly extend" the prior runway guidance. Runway, in other words, is sensitive to both terms — what you hold and what you spend — and to any event that changes either.

Doing the calculation from a 10-Q

To compute runway yourself rather than relying on the company's headline, go to the most recent Form 10-Q (or 10-K). On the balance sheet, sum cash, cash equivalents, and short-term marketable securities to get the numerator. On the statement of cash flows, take net cash used in operating activities for the period and, ideally, annualize or quarter-average it across recent periods to smooth lumpy timing (clinical milestones, payables swings, and one-time items can distort a single quarter). Dividing liquid resources by per-quarter burn yields the number of quarters of runway; converting to a calendar date gives the "funds operations into [year]" framing companies use. Including net cash used in investing activities tied to operations (such as equipment purchases) gives a more conservative burn figure than operating cash flow alone.

Two refinements matter. First, use net cash used in operations, not the net loss from the income statement — the loss includes non-cash items like stock-based compensation and depreciation that do not consume cash, so it overstates burn. The cash flow statement already strips those out. Second, watch for incoming cash that resets the numerator: an upfront license payment, a milestone receipt, or a financing each adds to liquid resources, which is exactly why a deal can move a runway estimate years out even if quarterly burn is unchanged. The Septerna disclosure above is a textbook case — same burn, larger numerator, longer runway.

Reading management's own runway guidance

A subtle but important distinction lives in the words companies choose. "Funds operations into 2028" means the cash is expected to last to some point within that year; "through 2028" means to the end of it; and "at least twelve months from the date of this filing" is the narrower assurance tied to the going-concern look-forward period rather than a calendar target. These are not interchangeable, and a careful reader treats "into" as the least committal of the three. The measurement date matters too: a runway estimate is anchored to a specific balance-sheet date, and burn between that date and the day you read the filing has already shortened it. For a fuller picture, compare the runway statement against the cash trend across the last several 10-Qs — a falling cash balance quarter over quarter, set beside an unchanged "into 2028," implies either an expected inflow or rising confidence that should itself be disclosed somewhere in the filing.

Most biotechs publish their own runway statement, typically phrased as expecting cash to fund operations "into" or "through" a stated period. That figure is useful but not neutral: it embeds management's assumptions about future spending (which may rise as trials advance), about cash still to be received (milestones, upfronts), and about the date of measurement. The value of doing the calculation from the filing is that it lets a reader test those assumptions — recompute with the disclosed cash and the disclosed burn, and see whether the company's stated runway is conservative or optimistic against its own numbers. Where a company also files going-concern language, that disclosure is the auditor's and management's formal signal that, on current assumptions, the runway may not extend far enough — a separate but related read.

The bottom line: runway is a derived number, and the inputs are in the filing. Liquid resources from the balance sheet, cash burn from the cash flow statement, and any incoming cash from a deal or financing are all disclosed on sec.gov. A company's headline "into 2028" is the answer to a calculation the reader can reproduce — and reproducing it is how you tell a comfortable balance sheet from a tight one before the next raise.