Burn Rate and Runway Calculator Widget
Give founders a runway check they can trust. Cash in the bank, monthly revenue and monthly operating expenses become gross burn, net burn, months of runway and the calendar month the money runs out, with a cash-balance curve and an optional monthly revenue growth rate.
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<iframe src="https://a2z.tools/embed/w/burn-rate-calculator" title="Burn Rate and Runway Calculator by A2Z Tools" width="100%" height="650" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>
A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.
<div data-a2z-widget="burn-rate-calculator" data-height="650"></div> <script async src="https://a2z.tools/embed.js"></script>
Adds a small script (what it does) that sizes the widget to fit its content, loads it lazily and keeps it isolated from your page's CSS.
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How it works
Gross burn is everything that leaves the bank in a month: payroll, rent, software, marketing. Net burn subtracts the cash revenue collected. With 600,000 in the bank, 70,000 of expenses and 20,000 of revenue, net burn is 50,000 and runway is 600,000 / 50,000 = 12 months. The zero-cash date counts that many months forward from today's date on the reader's device, adding any part month as days. With a revenue growth rate the widget follows Paul Graham's default-alive test instead of dividing: expenses stay flat, revenue grows by the same percentage every month, and each month's shortfall comes out of the cash balance. If revenue overtakes expenses before cash reaches zero, the company is default alive and the widget shows the month it breaks even and the cash left; otherwise it shows the month the money runs out, to a fraction of a month. The chart plots the projected balance for up to 60 months. Runway under six months triggers a warning, since raising a round often takes that long.
Calculation method
- Gross burn = monthly operating expenses
- Net burn = monthly operating expenses - monthly revenue
- Runway (no growth) = cash / net burn
- With growth g: revenue in month k = revenue x (1 + g)^(k-1); cash falls by (expenses - revenue in month k) each month; runway is the month cash reaches zero, interpolated within the month
- Break-even month = first month revenue >= expenses (default alive)
- Zero-cash date = today + whole months + remaining fraction x 30.44 days
Worked examples
Flat revenue
Inputs: Cash 600,000; revenue 20,000 a month; expenses 70,000 a month; no growth
Result: Gross burn 70,000; net burn 50,000; runway 12.0 months
Run on 1 October 2026, the zero-cash date is 1 October 2027.
Default alive
Inputs: Cash 1,000; revenue 40; expenses 50; revenue growth 10% a month
Result: Break-even in month 4 with 982.40 of cash left
Shortfalls of 10, 6 and 1.60 in months 1-3, then revenue of 53.24 exceeds expenses.
An illustration for planning, not financial advice.
Limitations
- Expenses are held flat; planned hires or price changes are not modelled.
- Revenue is cash collected; annual prepayments and slow-paying invoices make real cash flow lumpier.
- Projection is capped at 50 years and the chart at 60 months.
Where publishers use it
- Accelerator and incubator resource pages
- Founder newsletters on when to start fundraising
- Startup CFO and fractional-finance service websites
- University entrepreneurship courses
- Nonprofit and grant-funded projects tracking months of reserves
Questions
What is the difference between gross and net burn?
Gross burn is total monthly spending; net burn is spending minus revenue, the amount the bank balance actually falls. A company spending 70,000 with 20,000 of revenue has a gross burn of 70,000 and a net burn of 50,000.
How does revenue growth change the runway?
Each month revenue grows, net burn shrinks. With 600,000 cash, 70,000 expenses and 20,000 revenue growing 5% a month, revenue would need about 27 months to reach 70,000, so cash still runs out first - but at 14.4 months instead of 12.
What does default alive mean?
Paul Graham's term for a startup that reaches profitability on the cash it already has, assuming expenses stay flat and revenue keeps growing at its recent rate. If the widget shows Break-even first, the company is default alive at the rate entered.
How much runway should a startup keep?
Common advice is to start raising with at least 6-9 months left and aim for 18-24 months after a round, because fundraising can take 3-6 months and markets can close.
What is the burn multiple?
Net burn divided by net new ARR over the same period, a capital-efficiency ratio popularised by investor David Sacks. Burning 600,000 in a year to add 400,000 of ARR is a burn multiple of 1.5; under 1 is usually called excellent and above 2 a warning sign.
Should one-off costs be in monthly expenses?
Use a normal month. Spread annual items such as insurance or audit fees over 12 months, and treat a one-off purchase as a reduction of the starting cash instead.
Sources
- Default Alive or Default Dead? (October 2015) - Paul Graham (Y Combinator co-founder) . Defines the default-alive test: assuming expenses stay constant and revenue keeps growing at the rate of recent months, does the company reach profitability on the money it has left. Checked 2026-10-01.
Cite or recommend this tool
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A2Z Tools Burn Rate and Runway Calculator https://a2z.tools/embed/burn-rate-calculator
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[A2Z Tools Burn Rate and Runway Calculator](https://a2z.tools/embed/burn-rate-calculator)
Burn Rate and Runway Calculator by A2Z Tools - https://a2z.tools/embed/burn-rate-calculator
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