Cash Runway Calculator — How Many Months of Cash Are Left

Background.

Runway is the number of months a company can keep operating before it runs out of money, and it is the most consequential single figure on a startup's dashboard: it sets the deadline for every fundraise, every hiring decision and every strategic pivot. This calculator divides the cash you can actually spend by the cash you actually consume, and — unlike the back-of-envelope version — lets the burn compound. Enter $4,800,000 of cash against $160,000 of net monthly burn growing 3% a month and the answer is 21.71 months, not the 30 months a flat division gives you. That 8.29-month gap is the entire point of the tool.

The arithmetic is simple only when burn is flat. With flat burn, runway is spendable cash divided by net monthly burn. But almost no company plans for flat burn: hiring is scheduled, cloud costs scale with usage, and marketing budgets step up after a raise. When burn grows at a constant rate g each month, month i costs B(1+g) to the power of i−1, the cumulative spend after n months is the geometric sum B·((1+g)ⁿ − 1)/g, and setting that equal to your spendable cash and solving for n gives n = ln(1 + S·g/B) ÷ ln(1 + g). The calculator solves that logarithm exactly. In the worked example, burn has climbed from $160,000 to $295,146 a month by the time the money runs out — a company that budgeted from its current burn would be running a plan that is 84% too optimistic in its final month.

Two inputs deserve care. Cash on hand means unrestricted cash and equivalents you hold today: not an undrawn credit facility, not a signed term sheet, not receivables you expect to collect. Net monthly burn means cash consumed after customer collections, stated as a positive number, and it should be a trailing three-month average rather than last month — a single month distorted by an annual insurance premium or a clustered set of renewals will move your runway by quarters. The reserve floor is the input most founders skip and most boards insist on: it is the cash you refuse to spend because an orderly wind-down still costs money — final payroll, severance, notice-period rent, and the professional fees of closing a company. Runway measured to zero is a fiction, because a company that reaches zero cannot pay the people it must let go.

What this page does not do is derive your burn. Runway is a stock divided by a flow; the flow belongs to the burn rate calculator, which starts from cash outflows and collections and separates gross burn from net burn. Feeding a gross burn figure into a runway calculation is the most common way to frighten yourself unnecessarily, and feeding an accrual operating loss into it is the most common way to reassure yourself falsely — neither is the number this page wants.

The 12-month marker in the result is not arbitrary. FASB ASC 205-40, introduced by ASU 2014-15, requires management to evaluate at every annual and interim reporting period whether conditions indicate it is probable the entity will be unable to meet its obligations within one year after the financial statements are issued, and to disclose substantial doubt about going concern when they do. Independently, SEC Regulation S-K Item 303(b)(1) requires registrants to describe liquidity and capital resources "short-term (i.e., the next 12 months from the most recent fiscal period end required to be presented) and separately in the long-term (i.e., beyond the next 12 months)". Crossing below twelve months therefore changes your reporting obligations, not just your mood. Paul Graham's October 2015 essay frames the same threshold from the founder's side: a startup is "default alive" if it reaches profitability on current trajectory before the money runs out, and "default dead" if it does not — and he argues founders should start asking which one they are far earlier than feels comfortable.

One modelling limit is worth stating plainly before you read the number. This calculator applies a single constant growth rate to burn. Real burn moves in steps — a hiring wave, a layoff, a large annual renewal — and a constant rate cannot represent a step. If your plan contains a discrete change, run the calculator once for each regime rather than trusting a blended rate, and treat any result beyond about eighteen months as a direction rather than a date.

What is cash runway calculator?

Cash runway is the length of time, usually stated in months, that a company can continue operating at its current rate of cash consumption before its available cash is exhausted. In its simplest form it is spendable cash divided by net monthly burn. Spendable cash means unrestricted cash and equivalents, less any reserve deliberately held back for an orderly wind-down. Net monthly burn means the cash consumed each month after customer collections are netted off — the amount by which the bank balance actually falls. Runway is a forward-looking planning measure, not an accounting one: no standard-setter defines it, it appears in no financial statement, and two companies can compute it differently in good faith. It is nonetheless the number that governs a startup's decision calendar, because fundraising takes three to six months and a board will normally want a process launched while at least six months of runway remain. The refinement this calculator adds is compounding: because most operating plans grow burn month over month, the flat division systematically overstates how long the money lasts, and the overstatement grows with both the growth rate and the size of the balance.

How to use this calculator.

1. 01Enter unrestricted cash and equivalents you hold today. Do not include an undrawn credit line, a signed but unfunded term sheet, or receivables you expect to collect — none of those pay salaries on the day the balance hits zero.
2. 02Enter net monthly burn as a positive number: cash consumed per month after customer collections. Use a trailing three-month average. If you do not have this figure, compute it first in the burn rate calculator, which separates gross from net burn.
3. 03Set the monthly change in burn. Zero means a genuinely flat plan. A positive number reflects a hiring plan or scaling infrastructure costs. A negative number reflects a cost reduction you have already executed — not one you intend to execute.
4. 04Set a reserve floor if your board has agreed one. This is the cash ring-fenced for final payroll, severance, notice-period rent and the professional fees of a wind-down. Runway is then measured to that floor rather than to zero.
5. 05Read runway against the flat-burn figure. The gap between them is the cost of your burn-growth assumption, expressed in months, and it is usually the most actionable number on the page.
6. 06Check the burn in the final month. If it is far above today's burn, your plan is compounding a commitment you have not yet made — that is the lever you can still pull.
7. 07Compare the result against the 12-month marker in the status line, and against your fundraising calendar. A raise takes three to six months from first meeting to money in the bank, so the decision point arrives well before the runway does.

The formula.

With flat burn the result is a single division: runway = spendable cash ÷ net monthly burn, where spendable cash is cash on hand minus the reserve floor. With growing burn the months are no longer equal, so the calculation becomes a geometric series. If burn today is B and grows by a factor (1+g) each month, the cash consumed in month i is B(1+g) raised to the power (i−1), and the total consumed over n months is B·((1+g)ⁿ − 1)/g. Setting that total equal to spendable cash S and solving for n gives n = ln(1 + S·g/B) ÷ ln(1 + g). The calculator evaluates that logarithm directly rather than iterating month by month, so the answer is continuous — 21.71 months, not "somewhere in month 22". Rounding happens only at the return boundary: every intermediate value, including both logarithms, is carried at full arbitrary decimal precision, and months and currency are each rounded to two decimal places at the end. The status sentence is generated from the ROUNDED month figure rather than the raw one, so it can never contradict the number displayed above it. One boundary deserves naming: when burn shrinks, the geometric series can converge to a total below your cash, meaning the money is mathematically never exhausted. That happens whenever g is at or below −B/S. The calculator caps such cases at a 600-month model horizon and says so in the status line rather than returning an infinity.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Financial Accounting Standards Board (August 2014). Accounting Standards Update No. 2014-15, "Presentation of Financial Statements — Going Concern (Subtopic 205-40)." Source for the one-year-after-issuance substantial-doubt evaluation performed each annual and interim period. Authoritative PDF; URL verified live 29 July 2026 (binary PDF — text cross-checked against PwC Viewpoint's ASC 205-40 chapter, which is an independent reading of the same standard).
2. [2]17 CFR § 229.303(b)(1) (Regulation S-K Item 303, as amended by SEC Release 33-10890). Quoted verbatim on this page: liquidity and capital resources must be described "short-term (i.e., the next 12 months from the most recent fiscal period end required to be presented) and separately in the long-term (i.e., beyond the next 12 months)". Text fetched and verified 29 July 2026 via the Cornell LII mirror of the eCFR; sec.gov itself returns HTTP 403 to automated fetchers but is browser-accessible.
3. [3]Graham, P. (October 2015). "Default Alive or Default Dead?" Source for the default-alive / default-dead framing and for the argument that founders should ask the question early. Retrieved 29 July 2026.
4. [4]Jordan, J., Hariharan, A., Chen, F., & Kasireddy, P. (21 August 2015). "16 Startup Metrics." Andreessen Horowitz. Source for the gross-burn and net-burn definitions that determine which figure belongs in the denominator here. Retrieved 29 July 2026; quotes verified verbatim.
5. [5]Sacks, D. (23 April 2020). "The Burn Multiple." Craft Ventures. Consulted as an independent second authority on the sign and meaning of net burn — the burn multiple (net burn ÷ net new ARR) is only interpretable when net burn is stated as a positive number of dollars consumed, the convention used here. Retrieved 29 July 2026.
6. [6]U.S. Securities and Exchange Commission (30 January 2020). Release No. 33-10751, "Commission Guidance on Management's Discussion and Analysis of Financial Condition and Results of Operations" — requires a registrant presenting a metric such as runway or burn to disclose its definition and method of calculation. Effective 25 February 2020. sec.gov blocks automated fetchers (HTTP 403); release number, title and dates verified independently.