Startup Runway Calculator

How This Model Works

This calculator projects your startup's financial trajectory month by month. It takes four inputs — your current cash on hand, monthly burn rate, monthly revenue, and revenue growth rate — and simulates forward up to 120 months to determine when (or whether) your cash hits zero.

Each month, the model subtracts your burn from your cash and adds your revenue. If you've entered a growth rate, revenue compounds monthly — meaning your revenue in month n is calculated as revenue × (1 + growth rate)ⁿ. This is the same compounding function behind interest rates, population growth, and viral spread. Small differences in the growth rate produce dramatically different outcomes over time.

The Growth Lever: Why 2% Feels Like Nothing and 10% Changes Everything

Revenue growth is the most powerful input in this model because it compounds exponentially. At 5% monthly growth, $10,000 in revenue becomes $18,000 in 12 months. At 10%, that same $10,000 becomes $31,000. At 15%, it's $54,000. The curve isn't linear — it accelerates. This is why investors obsess over growth rate: it's the difference between a company that runs out of cash in 10 months and one that becomes self-sustaining in 18.

The flip side is equally important. Zero growth with revenue below burn is just a slower death. You're drawing down a finite pool of cash with no mechanism to reverse the decline. The table and chart above make this viscerally clear — you can watch the cash line march toward zero with no hope of recovery.

Default Alive vs. Default Dead

Paul Graham introduced these terms in a 2015 essay, and they remain the clearest framework for thinking about startup survival. The question is simple: if nothing changes about your current trajectory — same burn, same revenue, same growth rate — do you run out of money or not?

Default Dead means your projected cash hits zero before revenue overtakes burn. You are on a countdown. You either need to raise money, cut costs, or accelerate growth — and you need to do it before the clock runs out. The calculator shows this as a red badge with a specific number of months remaining and a projected cash-out date.

Default Alive means your revenue growth, if sustained, will overtake your burn before you exhaust your cash. The cash line dips but then curves back up as revenue exceeds expenses. The calculator shows this as a green badge with an infinite (∞) runway — not because your cash is infinite, but because the model projects you'll never run out. You've crossed the threshold from consuming capital to generating it.

Common Scenarios

Pre-revenue startup burning through a seed round. Cash on hand is your raise, burn is your monthly spend, revenue is zero, growth is zero. This is the simplest case — runway equals cash divided by burn. A $500K raise at $50K/month gives you 10 months. The chart shows a straight line to zero. Most first-time founders are here, and the number is always smaller than they expected.

Early revenue with modest growth. You've found some customers but revenue is well below burn. Set your current MRR and a conservative growth rate (3-5%). Watch how long the cash lasts. Then try 8-10% and see what changes. This is where the exponential curve starts to matter. The difference between 5% and 10% monthly growth isn't double the revenue — it's the difference between running out of money and becoming self-sustaining.

Post-product-market-fit with strong growth. Revenue is meaningful but still below burn because you're investing aggressively in growth. Set a higher growth rate (10-20%) and watch the inflection point — the month where revenue crosses burn. This is the moment your startup transitions from consuming cash to generating it. Every month after that, your cash balance grows instead of shrinking. The chart makes this crossover point visually obvious.

Profitable but fragile. Revenue exceeds burn, but barely. Set revenue slightly above burn with low or no growth. The calculator shows Default Alive, but the margin is thin. One bad month — a churned customer, an unexpected expense — and you flip back to Default Dead. This is the "going concern" zone: technically sustainable but without the cushion to absorb shocks. The model treats this as infinite runway, but experienced founders know that a 5% margin of safety isn't really safe.

What This Model Doesn't Account For

This is a deterministic projection, not a forecast. It assumes constant burn, steady compounding growth, and no external events. Real startups face lumpy revenue, seasonal variation, unexpected costs, hiring ramps, and fundraising dynamics that this model can't capture. Use it to build intuition about your trajectory, not to plan your exact cash-out date.

The growth rate assumption is the biggest variable. Sustained 10% monthly growth over 24 months is exceptional — most companies see growth rates decelerate as they scale. If you're modeling optimistic scenarios, also run the pessimistic ones. See what happens when growth drops to 3%. See what happens when it goes to zero. The gap between those scenarios is your risk exposure.

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