How to Calculate Burn Rate and Runway

Burn rate is how much cash your company loses per month. Net burn = cash out minus cash in, averaged over the last 3 months. Runway = current cash balance divided by net burn, expressed in months.

That is the whole formula. The reason founders still get it wrong is that "cash out" and "cash in" hide judgment calls, and each wrong call makes runway look longer than it is. This guide covers the two burn definitions, a worked example, the 3-month averaging method, and the three mistakes that quietly inflate runway.

Gross burn vs net burn: which one to report

Gross burn is total cash spent per month, ignoring revenue. Net burn is cash spent minus cash collected. Both matter, for different reasons:

• Net burn drives runway. It is the number your board wants first.
• Gross burn measures your cost base. If revenue drops 40% next quarter, gross burn tells you how bad it gets.

A company collecting $50,000 a month against $130,000 of monthly spend has a gross burn of $130,000 and a net burn of $80,000. Report both, but do runway math on net burn.

Metric	Formula	Example	Use it for
Gross burn	Total monthly cash out	$130,000	Sizing your cost base and worst case
Net burn	Cash out - cash in	$130,000 - $50,000 = $80,000	Runway math, board reporting
Runway	Cash balance / net burn	$960,000 / $80,000 = 12 months	Fundraise timing, hiring decisions
Default alive test	Does runway outlast the path to breakeven?	Breakeven in 15 months > 12 months runway = default dead	Deciding whether growth or cuts come first

How to calculate burn rate: the 3-month average method

Never compute burn from a single month. One month contains too much noise: an annual insurance premium, a customer prepaying a year upfront, a three-payroll month (they happen twice a year on biweekly payroll). The standard method:

1. Take ending cash 3 months ago and ending cash today, across all bank accounts.
2. Subtract any financing cash that landed in the window: new investment, loan draws. Add back loan principal repayments if you want operating burn.
3. Divide by 3.

Worked example

Cash on March 31: $1,140,000. Cash on June 30: $960,000. A $60,000 equipment loan was drawn in May.

• Raw change in cash: $1,140,000 - $960,000 = $180,000 over 3 months.
• Remove financing: the $60,000 loan masked burn, so true operating outflow was $180,000 + $60,000 = $240,000.
• Net burn: $240,000 / 3 = $80,000 per month.
• Runway: $960,000 / $80,000 = 12 months.

Skip the financing adjustment and you would report $60,000 of burn and 16 months of runway, a four-month error that could cost you a fundraise started too late. The bank-balance method works because it is derived from actual cash movement, the same logic a cash flow statement generator uses to reconcile net income to the change in cash.

How to calculate runway (and how much you actually need)

Runway in months = cash balance / average monthly net burn. Two adjustments make the number honest:

Use forward burn, not trailing burn, when spend is changing

Trailing average is the default, but if you signed three offer letters last week, your real burn is next quarter's, not last quarter's. Rebuild the number with committed changes: $80,000 trailing burn + $45,000 of new fully loaded salaries = $125,000 forward burn, and the same $960,000 now buys 7.7 months, not 12.

Fundraising math needs a buffer

A priced round typically takes 3 to 6 months from first meeting to money in the bank. The working rule: start raising with at least 9 months of runway, because you will negotiate from weakness below 6. Investors also ask for burn multiple (net burn / net new ARR); under 1.5x reads as efficient growth, over 3x reads as a problem in most 2026 boards.

Three mistakes that overstate runway

1. Counting AR as cash. Invoices are not money. If customers pay in 60 days, that $90,000 of receivables does nothing for the next two payrolls. Burn is a bank-balance calculation, full stop.
2. Treating deferred revenue prepayments as recurring. A customer prepaying $120,000 for the year drops net burn by $120,000 in one month. Averaging hides it for a quarter, then runway "suddenly" shortens. Flag prepayments separately when you compute the average.
3. Forgetting lumpy liabilities. Annual tax payments, insurance renewals, and quarterly bonus payouts are absent from most months and then take a full month's burn at once. Keep a 12-month cash calendar of every payment over about 5% of monthly burn.

What healthy burn looks like at each stage

Rough 2026 benchmarks, for venture-path software companies:

• Pre-revenue seed: $30,000 to $80,000 net burn, 18 to 24 months of runway post-raise.
• Post-seed, early revenue: burn multiple under 3x; runway never below 12 months without an active raise.
• Series A and later: burn multiple under 2x, trending to 1x as you approach $10M ARR.

Bootstrapped companies should treat sustained net burn as a countdown timer regardless of benchmarks: the only healthy steady state without outside capital is zero or negative net burn.

Report burn and runway every month, the same way

Burn belongs in every monthly update to investors, computed the same way each time so the trend is real. Show cash balance, net burn (3-month average), runway, and one sentence on what changed. Our investor update template has the full structure, and the investor reporting page shows what a complete monthly pack looks like. Consistency beats precision here: a board can work with a stable methodology, but not with a runway number that means something different every month.

Where AIStatements fits

Upload your accounting export to our financial statement generator and in about 60 seconds you get the formatted statement pack with burn, runway, and written analysis of what moved, computed the same way every month. It is software that formats and analyzes your data, not accounting or tax advice, so have a professional review anything you file.