Burn Rate Calculator

How to Use

Enter your starting cash balance, your current cash balance, and how many months have passed between them. The calculator shows your average monthly burn rate and how many more months your current balance can sustain that same rate before hitting zero, updating live as you type. If burn rate comes out at zero or negative, meaning the cash balance held steady or grew, runway shows as infinite, since there's no depletion rate to project forward from.

Why Burn Rate and Runway Matter So Much for Early-Stage Businesses

For an established, profitable business, burn rate is a minor operational metric. For an early-stage startup that's spending investor funding faster than it earns revenue, burn rate and its direct consequence, runway, are often the single most important numbers in the entire business, because they set a hard, unavoidable deadline. Unlike most business metrics that describe performance, runway describes time itself, specifically how much of it remains before difficult, urgent decisions become unavoidable. This is exactly why startup founders and investors track it so closely and so consistently, it's less a performance indicator and more an operational countdown clock.

Worked Example: From Two Balances to a Runway Figure

Using this tool's own defaults, a starting cash balance of 5,000,000 three months ago, and a current balance of 3,500,000 today. Total cash spent over that period is 5,000,000 − 3,500,000 = 1,500,000, and dividing that by the 3 months elapsed gives a monthly burn rate of 1,500,000 ÷ 3 = 500,000 per month. Runway then divides the current balance by that monthly rate: 3,500,000 ÷ 500,000 = 7 months remaining at the current pace. This single calculation compresses three months of financial history into one forward-looking, actionable number, exactly seven months until the business needs either more cash or a lower burn rate.

Why This Calculator Uses Net Burn, Not Gross Spending

Because this tool derives burn rate purely from the change in cash balance over time, it automatically captures net burn, spending minus any revenue collected during that same period, without needing revenue and expenses entered as two separate figures. This is a meaningfully more accurate real-world number than gross spending alone, a business bringing in some revenue while still spending more than it earns has a net burn rate lower than its raw spending, and that lower net figure is what actually determines how long the cash balance will last, which is exactly what runway is meant to project.

Using Runway as an Early Warning System, Not a Final Verdict

The real value of tracking runway isn't the number itself in any single month, it's watching the trend over consecutive months. A runway figure that's shrinking faster than expected, month over month, is an early signal to revisit spending or accelerate fundraising well before the situation becomes urgent. Recalculating this figure regularly, monthly at minimum for any business operating on a limited cash runway, turns it from a single static data point into an ongoing planning tool that gives real lead time to react.

A Note on the Time Period You Choose

The accuracy of the resulting burn rate depends heavily on choosing a representative time period for the "Months Elapsed" field, a very short window (a single unusual month with an atypical large expense or a one-time cash injection) can produce a burn rate that doesn't reflect ongoing, sustainable spending patterns. Using a longer period, three to six months where available, smooths out one-off anomalies and tends to produce a more reliable average burn rate and a more trustworthy runway projection than relying on the most recent single month alone.

Frequently Asked Questions

What is burn rate?

Burn rate is how much cash a business spends, net of any revenue, each month. It's calculated by taking the drop in cash balance over a period and dividing by the number of months in that period, commonly used by startups to track spending against their funding.

What is runway and why does it matter?

Runway is how many months a business can keep operating before it runs out of cash at the current burn rate, current cash balance divided by monthly burn rate. It's a key planning number for knowing when you need to raise funds or cut costs.

What's the difference between gross burn rate and net burn rate?

Gross burn rate is total monthly cash spending regardless of any revenue coming in. Net burn rate, what this calculator computes, is the actual net drop in cash balance each month, spending minus any revenue collected during the same period. A business with revenue can have a much lower net burn than gross burn, and a profitable business can even have negative net burn, meaning its cash balance is growing rather than shrinking.

How much runway should a startup aim to keep?

There's no universal number, but many startups and investors commonly reference a range of roughly 12 to 18 months of runway as a comfortable operating buffer, giving enough time to hit meaningful milestones and begin a fundraising process well before cash actually runs low. Shorter runway forces reactive, urgent fundraising or cost-cutting decisions, longer runway gives more room to make deliberate strategic choices instead of decisions driven purely by an approaching cash deadline.

Does burn rate assume spending stays constant every month?

Yes, this calculator produces an average monthly burn rate based on the total change in balance over the period entered, and projects runway assuming that same average rate continues going forward. Real spending is rarely perfectly uniform, a large one-time purchase or a new hire's onboarding costs can spike a single month well above the average, so treat the runway figure as a reasonable planning estimate rather than an exact countdown, and recalculate regularly as actual spending patterns become clearer.

What should a business do once runway starts getting short?

The two direct levers are extending the runway (raising additional funding, or reducing monthly burn rate through cost cuts) or reaching a stage that reduces reliance on the existing cash balance, growing revenue enough to shrink net burn, or reaching profitability outright. Most experienced operators recommend starting a fundraising process well before runway gets critically short, since raising funds itself typically takes months, waiting until cash is nearly exhausted removes negotiating leverage and narrows the available options considerably.