How many months can you keep building before you need to raise, sell, or quit? Plug in cash on hand, your real burn (rent and groceries count), current MRR, growth rate, and margin. The simulation does the rest.
Most founders calculate runway as “cash divided by burn.” That gives you a number, but the wrong one. It assumes your MRR stays at zero forever. The right calculation simulates each month forward: cash goes down by burn, but cash also goes up by gross-margin-adjusted MRR, and MRR compounds at your growth rate. The result is usually longer than the simple math — but only if your growth rate is real.
Methodology. Research-based assumptions. Calculations and rates synthesized from public vendor pricing pages and published founder data. How we research.
Cash on hand is everything you can spend on the business and yourself before it’s a problem — checking, savings, accessible investments. Don’t count emergency fund money you wouldn’t actually touch; that lies to you about runway. If you’d rather sell the SaaS than dip into a Roth IRA, the IRA isn’t runway.
Monthly burn is your real personal-plus-business cost, not your minimum survival number. Rent, groceries, healthcare, the SaaS tooling stack, the ads you’re running, contractor work. The most common founder mistake is including only business costs and ignoring that they’re a person who needs to eat. The default of $4,000 is a low-cost solo founder in a low-cost city; tweak hard for your situation.
Current MRR is what you’re collecting today. New launches start at $0; founders 6–12 months in might be at $500–$3,000. We dig into what counts in what is MRR.
Monthly growth rate is the load-bearing input. 5%/month compounds to 80% growth over 12 months — respectable but not insane. 10%/month compounds to 214%. 20%/month compounds to 791% and is the YC “hot startup” rate. Most bootstrapped solo SaaS at the 0–$10K stage grow at 3–8% per month if they’re working. Be honest here. The whole calculation hinges on this number being a real estimate, not aspirational.
Gross margin is what’s left of each subscription dollar after infrastructure costs. For most Next.js + Supabase + Stripe SaaS at low scale, 80–90% is realistic; we walked the numbers in SaaS cost at $1K MRR. AI-heavy products closer to 50–65%.
The calculator runs a 60-month simulation. Each month:
The interesting case is when MRR × margin overtakes burn. From that month forward you’re cash-flow positive and runway is theoretically infinite. The calculator surfaces that as the “break-even month.” If break-even arrives before cash runs out, congratulations — you have a viable business. If it arrives after cash runs out, the simulation tells you exactly how short you are.
Founders dramatically overstate their runway in three predictable ways:
1. They don’t count their salary. A founder who quit their $120K job and is “living off savings” will say “I have $40K in the bank and I burn $500/month on infrastructure, so 80 months of runway.” They’re not actually living on $500/month. They’re drawing $4,000–$5,000/month from savings to cover rent and food. Real runway is 8–10 months, not 80.
2. They assume costs stay flat. Your hosting bill grows. You’ll buy that boilerplate. You’ll need a logo. You’ll discover that you do, in fact, need health insurance after you turn 30. Add a 10–15% buffer to your monthly burn for “things I haven’t planned for yet.”
3. They assume linear MRR growth. “I’m at $500 MRR, I’ll add $500 a month, I’ll be at $6K by year-end.” Linear growth from a tiny base is how new founders think. Reality is that growth is either compounding (you’ll surprise yourself how fast you scale) or dying (each new customer is harder than the last and you plateau). Linear almost never happens. The calculator uses compound growth, which is more honest, but you have to feed it an honest growth rate. The zero-to-$1K MRR playbook gets into how founders actually clear that first revenue ramp.
Two founders, same situation: $30K cash, $4K burn, $0 MRR. Founder A grows MRR at 10%/month. Founder B grows at 3%/month. Both add their first customer in month 2 at $50.
By month 12, Founder A has $1,800 MRR, has covered $4,300 of burn, and is approaching break-even at month 18. Founder B has $90 MRR, has barely dented anything, and runs out of cash at month 7. The starting condition was identical. The growth rate ate everything.
This is the most consequential takeaway from playing with the calculator: spend less time worrying about saving an extra $5K of runway. Spend more time worrying about whether your growth rate is 3% or 10%. That’s where the runway actually comes from.
If the calculator tells you 6 months of runway and 14 months to break-even, you have an 8-month gap. There are exactly four levers:
Lever 1: Cut burn. The fastest, least fun option. Move to a cheaper city. Drop subscriptions. Take a part-time consulting gig that covers half your burn (extends runway proportionally). Each $500/month of burn cut directly extends runway by 1–2 months at typical scales.
Lever 2: Raise prices. If you’re at $9/month, the answer is almost always “charge more.” Doubling prices on new customers doesn’t double your churn for most B2B SaaS — we covered the dynamics in when to do a pricing increase. If your growth rate stays similar after the price hike, your effective MRR growth doubles.
Lever 3: Improve activation/conversion. If 100 people land on your site and 1 converts, doubling that to 2 directly doubles your growth rate at zero cost. This is where the calculator’s “growth rate” input is most malleable. Most solo SaaS have terrible onboarding and one weekend of work on the trial flow can move conversion rates 30–50%.
Lever 4: Add a one-time-revenue product. A $99 template, a $499 course, consulting at $200/hour, an audit service. One-time revenue extends runway directly without touching MRR. It also stalls the SaaS, so use it as a bridge, not a strategy.
If you’ve been working on the same SaaS for 9+ months, your MRR is under $1,000, and your growth rate is under 3%/month, the math is telling you something. Either your problem isn’t painful enough, your audience isn’t reachable, or your pricing is wrong. The runway calculator can’t tell you which — but it can tell you that hoping for a 10x improvement in month 14 is not a plan.
The honorable move is to set a runway floor (e.g., “I will not let cash drop below $10K”), and pivot the product or quit cleanly when you hit it. Founders who do this preserve optionality. Founders who burn to $0 and then take a high-stress contract gig under duress make worse decisions.
Runway isn’t a single number — it’s a relationship between cash, burn, and how fast revenue compounds. The calculator gives you a directional read. The lesson is mostly that growth rate compounds, burn doesn’t — small differences in monthly growth produce huge differences in time-to-break-even. Be honest about both.
The stack, prompts, pricing, and mistakes to avoid — for solo founders building with AI.