Burn Rate & Runway Calculator

Last updated: August 4, 2026  ·  Reviewed by the DoCalc team

What Are Burn Rate and Runway?

Burn rate is how much cash a company spends each month. Runway is how many months of operation remain before the bank account hits zero, at the current burn rate. Together, they're the single most important pair of numbers for any pre-profit startup, because every other decision — when to raise, how fast to hire, whether to cut costs — depends on knowing exactly how much time is left. Unlike most SaaS metrics, burn rate and runway aren't abstract efficiency scores; they're a literal countdown, which is why founders tend to check them more often than almost any other number in the business.

The Formula

Gross burn tells you the total cost of running the company each month. Net burn tells you the actual cash leaving the bank after revenue is subtracted — and it's net burn, not gross burn, that determines runway. A company spending $60,000/month with $20,000/month in revenue has a net burn of $40,000, not $60,000, and that $20,000 difference can add months of runway.

How Burn Rate and Runway Work Together

The relationship is mechanical: cash in the bank drains by exactly the net burn amount every month, until it hits zero. That makes runway a strict countdown rather than a soft target, and it's the reason burn rate deserves more frequent attention than most other metrics on this site — a business can carry a mediocre CAC payback period or a slightly-too-high churn rate for a while and still survive, but a business that runs out of cash simply stops operating, full stop, regardless of how good the other numbers look. This is also why net burn matters so much more than gross burn: two companies spending the same $60,000/month can have wildly different survival horizons if one has $20,000/month in revenue offsetting the spend and the other has none.

Worked Example: Calculating Runway Step by Step

Suppose a startup has $480,000 in the bank, spends $70,000/month across payroll, tools, and office costs, and brings in $25,000/month in revenue.

At the current pace, this company has just under 11 months before the account hits zero — squarely in the "caution" zone below, meaning a fundraising process or a path to breakeven needs to start now, not in six months. Now model what happens if the team lands three new enterprise deals worth $8,000/month in additional revenue combined, without adding any new cost:

Roughly $8,000/month in new revenue bought this company an extra 2.3 months of runway — a concrete illustration of why growing revenue is one of the three real levers for extending runway, alongside cutting costs and raising capital.

Use Cases: How Much Runway Is Enough?

Runway	Read
Under 9 months	Critical — start fundraising or cutting costs immediately
9–18 months	Caution — plan your next raise or path to profitability now
18+ months	Healthy — enough time to hit meaningful milestones before raising

The 18-month figure isn't arbitrary: a typical fundraise takes 3-6 months from first investor meeting to cash in the bank, and investors want to see 12+ months of remaining runway after the round closes, which means starting the process with at least 12-18 months left is standard advice for a reason. Founders use this number monthly, as part of routine cash management; boards use it every meeting to sanity-check the company's fundraising timeline; and investors use it during diligence to judge whether a raise is being driven by growth ambition or by genuine urgency.

Common Mistakes to Avoid

The most common mistake is calculating runway from gross burn instead of net burn, which understates runway for any company with real revenue — the fix is always to subtract revenue first. A second mistake is treating burn rate as a fixed number rather than a trend: a company burning $40,000/month with expenses rising 5% monthly has a very different runway trajectory than one holding flat at $40,000, even though this month's burn rate looks identical. A third mistake is excluding one-time or irregular expenses (annual software renewals, equipment purchases, legal fees) from the burn calculation just because they don't recur monthly — irregular costs still consume runway and should be smoothed into the average, not ignored.

How to Extend Runway

The three levers are the same as any cash-management problem: cut expenses (usually payroll, since it's typically 60-80% of a startup's cost base), grow revenue (which reduces net burn directly), or raise capital (which resets the clock but dilutes ownership). Most experienced founders model all three scenarios before deciding — cutting too aggressively can slow the growth that would have solved the problem faster than the cut did.

Pros and Cons of Tracking Runway This Way

Pros: a single, unambiguous number everyone from founders to investors reads the same way; forces a monthly discipline of knowing net burn, not just gross spend; makes fundraising timing decisions concrete instead of vague.

Cons: assumes burn stays flat, which it rarely does — a hiring plan or a big renewal can shift the real number significantly; says nothing about whether the spend is buying meaningful growth, only how long it can continue.

Who Should — and Shouldn't — Use This Calculator

Use it if you're pre-profit and need a fast, honest read on how much time is left before the next fundraise or breakeven — this is the single most load-bearing number for that conversation.

Use with extra caution if your expenses are lumpy (annual renewals, seasonal headcount) — a flat runway estimate from one month's burn can be badly wrong; model a trailing 3-month average instead of a single month's snapshot.

Expert Recommendation

Recalculate runway every month, not every quarter — burn rate can shift faster than most other metrics on this site, and a quarter is a long time to be running on a stale number when the stakes are literally "does the company survive." Treat 18 months as a trigger to start planning the next raise, not a comfortable cushion to stop watching the number.

Conclusion

Runway is the one metric on this site that isn't really about optimization — it's about survival math. Get net burn right, recalculate it often, and use it as an honest forcing function for hard decisions rather than a number to make peace with.

Frequently Asked Questions

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