Startup Runway and Cash Burn: How to Calculate It and Extend It

The runway formula

Runway is the number of months your company can operate before cash hits zero, assuming spend and revenue stay roughly where they are today. The core formula is simple.

Runway months equals current cash divided by average monthly net burn. If you hold $600,000 and burn $50,000 net per month, you have twelve months of runway. The division is easy; calculating burn honestly is the hard part.

• Runway months = current cash / average monthly net burn
• Current cash = total usable cash across operating accounts
• Use a trailing 3-month average for burn, not a single month
• Recompute whenever burn or revenue meaningfully shifts

Gross burn vs net burn

Gross burn is total cash going out the door each month: payroll, rent, software, contractors, everything. Net burn is gross burn minus the cash coming in from revenue. Net burn is the right number for runway because revenue offsets spend.

Watch the gap between the two. A company with high gross burn but strong revenue can have modest net burn, but it is fragile: if revenue dips, net burn jumps toward gross burn and runway contracts fast. Tracking both tells you how exposed you are.

Common ways founders miscalculate burn

The most frequent error is using one unusually light or heavy month. Annual software renewals, payroll timing, and one-off vendor payments distort a single month, so a trailing three-month average gives a truer picture.

The second error is counting cash you cannot actually spend, such as restricted deposits or funds earmarked for taxes. The third is ignoring known step-changes: a new hire starting next month or an annual contract renewing will change burn, and a forward-looking runway should account for them.

• Averaging too few months and catching an outlier
• Including restricted or already-committed cash
• Ignoring upcoming hires, raises, or renewals
• Confusing accrual profit with actual cash movement

Ways to extend runway

There are only three levers: spend less, earn more, or add capital. Most of the durable gains come from the first two because they improve the underlying business rather than just buying time.

On the cost side, audit recurring software, renegotiate vendor terms, and slow discretionary hiring before cutting into the team. On the revenue side, accelerating collections and reducing churn often moves net burn faster than new sales. Raising capital extends runway too, but it is easier to raise from a position of efficient burn than a position of desperation.

• Cut unused software and renegotiate vendor contracts
• Tighten collections to pull cash in sooner
• Reduce churn so existing revenue compounds
• Phase hiring to match real milestones
• Raise before runway gets short, not after

Why accurate books make runway trustworthy

Runway is only as reliable as the burn figure behind it, and burn is only accurate if your books are current and correctly categorized. Stale or messy books produce a runway number you cannot bet on.

Median categorizes and posts transactions every business day, so cash and net burn stay close to current instead of going stale between month-ends. With clean feeds from Stripe, Ramp, Mercury, Brex, and Plaid, the burn rate you plan against reflects where you are now, not a month-old estimate.